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The mechanisms causing non-responsiveness to hepatitis B surface antigen (HBsAg) vaccines in man remain elusive. The increased incidence of non-responsiveness in subjects with HLA-DR3+ or -DR7+ haplotypes suggests that immune response mechanisms governed by genes of the MHC are involved. Homozygotes for these two haplotypes are found almost exclusively in the non-responder (NR) population. It is conceivable that antigen-presenting cells (APC) of NR are defective in the uptake of HBsAg and that they are unable to present this Ag adequately. Previously, we demonstrated thatDR2+,DR7+ andDP4+ NR were able to present HBsAg. In the present paper we demonstrate that six DR0301+ NR, five of which are homozygous for this marker, were able to take up, process and present HBsAg to HBsAg-specific, DR0301-restricted T cell lines. Non-fractionated peripheral blood mononuclear cells (PBMC) from the DR0301+ NR did not proliferate to HBsAgin vitro, whereas they proliferated vigorously upon stimulation with tetanus toxoid, thus ruling out the presence of a generalized immunodeficiency. We therefore conclude that HLA-DR0301+ NR vaccinees are not deficient in their HBsAg-presentation. Because it was demonstrated that recently activated T cells can apparently bypass the requirement for B7, we may have overlooked the role of the B7-co-stimulation in our set-up that used HBsAg-specific T cell lines. Therefore we examined the expression of B7 co-stimulatory molecules on NR-APC. CD86 was normally present on these cells and was not down-regulated after culturing the PBMC in the presence of HBsAg. We conclude that CD86 expression on CD14+ monocytes of DR0301- and DR07-homozygous poor responders is not deficient and cannot be the mechanism underlying the non-responsiveness of these subjects. [ABSTRACT FROM AUTHOR]

CD8+ T cells can recognize peptides presented by class I human leukocyte antigen (HLA-I) of nucleated cells. Exploring this immune mechanism is essential for identifying T-cell vaccine targets in cancer immunotherapy. Over the past decade, the wealth of data generated by experiments has spawned many computational approaches for predicting HLA-I binding, antigen presentation and T-cell immune responses. Nevertheless, existing HLA-I binding and antigen presentation prediction approaches suffer from low precision due to the absence of T-cell receptor (TCR) recognition. Direct modeling of T-cell immune responses is less effective as TCR recognition's mechanism still remains underexplored. Therefore, directly applying these existing methods to screen cancer neoantigens is still challenging. Here, we propose a novel immune epitope prediction method termed IEPAPI by effectively incorporating antigen presentation and immunogenicity. First, IEPAPI employs a transformer-based feature extraction block to acquire representations of peptides and HLA-I proteins. Second, IEPAPI integrates the prediction of antigen presentation prediction into the input of immunogenicity prediction branch to simulate the connection between the biological processes in the T-cell immune response. Quantitative comparison results on an independent antigen presentation test dataset exhibit that IEPAPI outperformed the current state-of-the-art approaches NetMHCpan4.1 and mhcflurry2.0 on 100 (25/25) and 76% (19/25) of the HLA subtypes, respectively. Furthermore, IEPAPI demonstrates the best precision on two independent neoantigen datasets when compared with existing approaches, suggesting that IEPAPI provides a vital tool for T-cell vaccine design. [ABSTRACT FROM AUTHOR]

ability of MHC class II molecules to sort into the endocytic pathway has generally been attributed to the invariant chain glycoproteln. In this paper, we present evidence suggesting that lumenal sequence in the MHC class II molecule itself control the post-Goigi entry of class II into endosomes. Single amlno acid changes have been introduced into a highly conserved region of the class II β chain (amino acids 80–83). Mutant class II β chain genes and wild-type α chain genes have been transfected into cells that lack both class II and invariant chain expression. Immunofluorescent staining of transfected cells indicates that single amino acid changes in this region of β can positively or negatively modulate expression of class II in endocytic vesicles Independently of invariant chain. Mutation at residue 80 leads to prominent localization in vesicular structures typical of late endocytic compartments, while a change at position 82 leads to arrest in the Goigi. These data argue in favor of the possibility that MHC class II molecules bear a sorting signal that allows access to MHC class II molecules into the endocytic pathway of antigen presenting cells. [ABSTRACT FROM PUBLISHER]

Major histocompatibility complex (MHC) class II molecules play a pivotal role in antigen presentation and CD4+ T cell response. Accurate prediction of the immunogenicity of MHC class II-associated antigens is critical for vaccine design and cancer immunotherapies. However, current computational methods are limited by insufficient training data and algorithmic constraints, and the rules that govern which peptides are truly recognized by existing T cell receptors remain poorly understood. Here, we build a transfer learning-based, long short-term memory model named 'TLimmuno2' to predict whether epitope-MHC class II complex can elicit T cell response. Through leveraging binding affinity data, TLimmuno2 shows superior performance compared with existing models on independent validation datasets. TLimmuno2 can find real immunogenic neoantigen in real-world cancer immunotherapy data. The identification of significant MHC class II neoantigen-mediated immunoediting signal in the cancer genome atlas pan-cancer dataset further suggests the robustness of TLimmuno2 in identifying really immunogenic neoantigens that are undergoing negative selection during cancer evolution. Overall, TLimmuno2 is a powerful tool for the immunogenicity prediction of MHC class II presented epitopes and could promote the development of personalized immunotherapies. [ABSTRACT FROM AUTHOR]

Dendritic cells (DCs) express major histocompatibility complex class II (MHC-II) and are best known for proficiently presenting antigens to T cells, thereby eliciting specific adaptive T cell responses. Moreover, conventional DCs (cDCs) are specifically adept at handling intestinal antigens. Relatively recent discoveries and investigations have proven the existence of a new group of innate lymphocytes that reside in tissues like the intestine. They lack specific antigen receptors and can express MHC-II. These group 3 innate lymphoid cells (ILC3s) comprise a subset of heterogeneous innate lymphocytes that mirror the phenotype and functions of T-helper cells and act in the first line of defense. Considering that ILC3s are crucial for maintaining homeostasis of the intestinal mucosa and are found in niches alongside DCs, we herein describe the roles played by cDCs and ILC3s in the gut, highlighting the most recent studies. We discuss how these cells are alike and differ, constantly pointing out the thin, blurry line that separates cDCs and ILC3s. [ABSTRACT FROM AUTHOR]

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is known to play a key role in enhancing multiple immune functions that affect response to infectious pathogens including antigen presentation, complement- and antibody-mediated phagocytosis, microbicidal activity, and neutrophil chemotaxis. Reduced GM-CSF activity and immune response provides a mechanism for increased infection risk associated with autoimmune pulmonary alveolar proteinosis (aPAP) and other disorders involving the presence of GM-CSF autoantibodies. We present a case series of five patients with persistent or unusual pulmonary and central nervous system opportunistic infections (Cryptococcus gattii, Flavobacterium, Nocardia) and elevated GM-CSF autoantibody levels, as well as 27 cases identified on systematic review of the literature. [ABSTRACT FROM AUTHOR]

The discovery that major histocompatibility complex (MHC) class I-related molecule 1 (MR1) presents microbial antigens to mucosal-associated invariant T (MAIT) cells was a significant scientific milestone in the last decade. Surveillance for foreign metabolically derived antigens added a new class of target structures for immune recognition. The recent identification of a second family of MR1-restricted T cells, called MR1T cells, which show self-reactivity suggests the microbial antigens characterized so far may only represent a handful of the potential structures presented by MR1. Furthermore, the reactivity of MR1T cells towards tumours and not healthy cells indicates tight regulation in the generation of self-antigens and in MR1 expression and antigen loading. These novel and exciting observations invite consideration of new perspectives of MR1-restricted antigen presentation and its wider role within immunity and disease. [ABSTRACT FROM AUTHOR]

Epidermal melanocyte loss in vitiligo, triggered by stresses ranging from trauma to emotional stress, chemical exposure or metabolite imbalance, to the unknown, can stimulate oxidative stress in pigment cells, which secrete damage-associated molecular patterns that then initiate innate immune responses. Antigen presentation to melanocytes leads to stimulation of autoreactive T-cell responses, with further targeting of pigment cells. Studies show a pathogenic basis for cellular stress, innate immune responses and adaptive immunity in vitiligo. Improved understanding of the aetiological mechanisms in vitiligo has already resulted in successful use of the Jak inhibitors in vitiligo. In this review, we outline the current understanding of the pathological mechanisms in vitiligo and locate loci to which therapeutic attack might be directed. [ABSTRACT FROM AUTHOR]

Summary: The clinical significance of the specific anti‐John Milton Hagen (JMH) alloantibody in inherited JMH‐negative patients remains unclear. During clinical blood transfusion, it is often classified as an anti‐JMH autoantibody in acquired JMH‐negative patients, which might further lead to the occurrence of haemolysis events. In this study, we found that the proportion of inherited JMH‐negative people in the Guangzhou population was 0.41%, based on the study of 243 blood samples by flow cytometry. Gene sequencing analysis revealed two novel variants located in exon 11 (c.1348G>A, p.Ala449Thr) and exon 14 (c.1989G>T, p.Leu663Phe). Specific antigen presentation showed that JMH‐positive RBCs (red blood cells) could be internalized by SEMA7A−/− dendritic cells (DCs) and that SEMA7A−/− DCs activated by the semaphorin 7a (Sema7a) protein or JMH‐positive erythrocytes further induced activation of CD4+ T cells to secrete interferon (IFN)‐γ. Transfusion of JMH‐positive RBCs could lead to the production of the specific anti‐JMH alloantibody in Sema7a knock‐out (KO) C57 mice. After erythrocyte sensitization, complement C3 was specifically fixed, causing the destruction of JMH‐positive erythrocytes. The anti‐JMH alloantibody caused immunological destruction of JMH‐positive erythrocytes and promoted the clearance of JMH‐positive RBCs. We should be cautious when making conclusions about the clinical significance of the anti‐JMH alloantibody. [ABSTRACT FROM AUTHOR]

Lysosomes are dynamic organelles that are transported along microtubules bidirectionally via kinesin and dynein motor proteins. Lysosomal positioning, which is determined by the balance of the bidirectional lysosomal movement, changes under various conditions and affects lysosomal functions such as autophagy and antigen presentation. A recent study by Takemasu et al. (Phosphorylation of TMEM55B by Erk/MAPK regulates lysosomal positioning. J. Biochem. 2019; 166:175–185) has shown that phosphorylation of the transmembrane protein TMEM55B is involved in the retrograde lysosomal trafficking towards the perinuclear region. They found that TMEM55B is phosphorylated upon stimulation with various ligands and that Erk/MAPK mediates the TMEM55B phosphorylation. They have also revealed that a phosphorylation mimic mutant of TMEM55B enhances perinuclear lysosomal clustering compared to the wild-type TMEM55B. These findings suggest that TMEM55B phosphorylation by Erk/MAPK is responsible for regulating lysosomal positioning in response to external stimuli. [ABSTRACT FROM AUTHOR]

Summary: Dendritic cells (DCs) are the key professional antigen‐presenting cells which bridge innate and adaptive immune responses, inducing the priming and differentiation of naive to effector CD4+ T cells, the cross‐priming of CD8+ T cells and the promotion of B cell antibody responses. DCs also play a critical role in the maintenance of immune homeostasis and tolerance. DC–T cell interactions underpin the generation of an autoimmune response in rheumatoid arthritis (RA). Here we describe the function of DCs and review evidence for DC and T cell involvement in RA pathogenesis, in particular through the presentation of self‐peptide by DCs that triggers differentiation and activation of autoreactive T cells. Finally, we discuss the emerging field of targeting the DC–T cell interaction for antigen‐specific immunotherapy of RA. DC–T cell interactions underpin the generation of an autoimmune response in rheumatoid arthritis (RA). We describe the function of DCs and review evidence for DC and T cell involvement in RA pathogenesis, in particular through the presentation of self‐peptide by DCs that triggers differentiation and activation of autoreactive T cells. We then discuss the emerging field of targeting the DC–T cell interaction for antigen‐specific immunotherapy of RA. [ABSTRACT FROM AUTHOR]

Slan+ non‐classical monocytes are equipped with a distinctive immunological gene set compared to DCs, and harbor monocyte‐like functional features. Human 6‐sulfo LacNac‐positive (slan+) cells have been subject to a paradigm debate. They have previously been classified as a distinct dendritic cell (DC) subset. However, evidence has emerged that they may be more related to monocytes than to DCs. To gain deeper insight into the functional specialization of slan+ cells, we have compared them with both conventional myeloid DC subsets (CD1c+ and CD141+) in human peripheral blood (PB). With the use of genome‐wide transcriptional profiling, as well as functional tests, we clearly show that slan+ cells form a distinct, non‐DC‐like population. They cluster away from both DC subsets, and their gene‐expression profile evidently suggests involvement in distinct inflammatory processes. An extensive transcriptional meta‐analysis confirmed the relationship of slan+ cells with the monocytic compartment rather than with DCs. From a functional perspective, their ability to prime CD4+ and CD8+ T cells is relatively low. Combined with the finding that "antigen presentation by MHC class II" is at the top of under‐represented pathways in slan+ cells, this points to a minimal role in directing adaptive T cell immunity. Rather, the higher expression levels of complement receptors on their cell surface, together with their high secretion of IL‐1β and IL‐6, imply a specific role in innate inflammatory processes, which is consistent with their recent identification as non‐classical monocytes. This study extends our knowledge on DC/monocyte subset biology under steady‐state conditions and contributes to our understanding of their role in immune‐mediated diseases and their potential use in immunotherapeutic strategies. [ABSTRACT FROM AUTHOR]

Review of in vivo targeting of tumor antigens to lectin receptors on antigen‐presenting cells using antibodies or ligands may improve the antitumor efficacy of vaccines. There is a growing understanding of why certain patients do or do not respond to checkpoint inhibition therapy. This opens new opportunities to reconsider and redevelop vaccine strategies to prime an anticancer immune response. Combination of such vaccines with checkpoint inhibitors will both provide the fuel and release the brake for an efficient anticancer response. Here, we discuss vaccine strategies that use C‐type lectin receptor (CLR) targeting of APCs, such as dendritic cells and macrophages. APCs are a necessity for the priming of antigen‐specific cytotoxic and helper T cells. Because CLRs are natural carbohydrate‐recognition receptors highly expressed by multiple subsets of APCs and involved in uptake and processing of Ags for presentation, these receptors seem particularly interesting for targeting purposes. [ABSTRACT FROM AUTHOR]

ERAP1 controls both the repertoire and the extent of T cell responses to antigensEndoplasmic reticulum aminopeptidase 1 (ERAP1) is a critical component of the adaptive immune system that has been shown to increase or decrease the presentation of specific peptides on MHC class I molecules. Here, we have demonstrated that ERAP1 functions are not only important during the presentation of antigen-derived peptides, but these functions can also completely change which antigen-derived peptides ultimately become selected as immunodominant T-cell epitopes. Our results suggest that ERAP1 may do this by destroying epitopes that would otherwise become immunodominant in the absence of adequate ERAP1 functionality. We further establish that ERAP1-mediated influences on T-cell functions are both qualitative and quantitative, by demonstrating that loss of ERAP1 function redirects CTL killing toward a different set of antigen-derived epitopes and increases the percent of antigen-specific memory T cells elicited by antigen exposure. As a result, our studies suggest that normal ERAP1 activity can act to suppress the numbers of T effector memory cells that respond to a given antigen. This unique finding may shed light on why certain ERAP1 single nucleotide polymorphisms are associated with several autoimmune diseases, for example, by significantly altering the robustness and quality of CD8+ T-cell memory responses to antigen-derived peptides. [ABSTRACT FROM AUTHOR]

The primary aim of this study was to evaluate the role of natural killer (NK) cells on antigen-specific adaptive immune responses. After analysing the mechanism of impaired adaptive immune responses of NK-depleted mice, an immune interventional approach was developed to restore adaptive immunity in NK-depleted mice. NK cells were depleted from mice by administration of anti-asialo GM1 antibody (100 μl/mouse), twice, at an interval of 48 h. Hepatitis B surface antigen (HBsAg) was administered intraperitoneally to normal C57BL/6 mice (control mice) and NK-depleted mice. The levels of antibody to HBsAg (anti-HBs) in the sera and HBsAg-specific lymphocytes in the spleen were assessed. The functions of T lymphocytes, B lymphocytes and dendritic cells (DCs) were evaluated in vitro. HBsAg-pulsed DCs were prepared by culturing spleen DCs with HBsAg for 48 h and administered once to NK-depleted mice. The levels of anti-HBs in the sera and HBsAg-specific lymphocytes were significantly lower in NK-depleted mice compared with control mice ( P < 0·05). The functions of T and B lymphocytes were similar between control mice and NK-depleted mice. However, the functions of spleen DC and liver DC were significantly lower in NK-depleted mice compared with control mice ( P < 0·05). Administration of HBsAg-pulsed DCs, but not HBsAg, induced HBsAg-specific humoral and cellular immune responses in NK-depleted mice. Our study suggests that cross-talk between NK cells and DCs regulates the magnitude of adaptive immunity. In addition, antigen-pulsed immunogenic DCs represent potent immune modulator even if subjects with diminished innate immunity. [ABSTRACT FROM AUTHOR]

Epstein-Barr Virus (EBV)-transformed B lymphoblastoid cell lines (BLCL) are currently used for numerous applications in cellular immunology. Where protocols destined for clinical application are concerned, the final choice of assay is made according to a risk/benefit ratio analysis. In this balance the use of xenogenic or allogenic serum has always been a major concern, as it carries both an infectious and an immunological risk. So far, it is unknown whether serum can be omitted from the entire BLCL selection procedure. In addition, as BLCL have been described as heterogeneous, serum deprivation may affect their antigen-presenting capacity. In the present study, BLCL were generated in the absence or presence of fetal calf serum (referred to as BLCL0 or BLCLFCS, respectively). Next, in order to assess the antigen-presenting capacity of these cells, we compared the ability of BLCL0 and BLCLFCS cells to stimulate the EBV-specific repertoire of the corresponding donor's peripheral blood mononuclear cells in vitro. Our results showed that addition of serum was not essential for BLCL infection and culture, and that as far as we could determine, BLCL0 cells were as effective as BLCLFCS in reactivating the EBV-specific T-cell repertoire in vitro. Notably, FCS-specific T-lymphocytes can be detected among the BLCLFCS-specific CD4+-CTL. Not only was this latter observation unexpected for an EBV-seropositive donor, but it implied that the BLCL had captured and processed the corresponding FCS-derived solubles antigens; taken together our results emphasized the interest of the possibility to generate BLCL0, both for research and for clinical applications. [ABSTRACT FROM AUTHOR]

In vaccine development, a major objective is to induce strong, specific T cell responses. This might be obtained by targeting antigen to cell surface molecules that efficiently channel the antigen into endocytic compartments for loading of MHC molecules. Antibodies have been used to deliver antigen; however, it is important to define optimal targets on antigen‐presenting cells (APC) for efficient delivery. For this purpose, we have established a T cell readout that can be used to screen large numbers of different mAb for their ability to load MHC class II molecules. The novel human CD4+ T cell clone is specific for mouse Ig Cκ (40–48) and restricted by HLA‐DR4 (DRA1,B1*0401). DR4 apparently presents both mouse and human Cκ 40–48, but there is no cross‐reaction at the T cell level. B cells from DR4 transgenic mice spontaneously process and present the mouse Cκ peptide. The mouse Cκ‐specific T cell readout was used to demonstrate that mouse mAb specific for human dendritic cell (DC)‐specific ICAM‐grabbing non‐integrin (DC‐SIGN), a novel DC‐specific molecule, were 10‐ to 1000‐fold more potent at inducing κ‐specific human CD4+ T cell proliferation compared to control mAb. Consistent with this finding, DC‐SIGN‐specific mAb were rapidly internalized upon binding and found in intracellular vesicles. These results strongly argue that DC‐SIGN‐specific mAb are channeled into the MHC class II presentation pathway. Thus, DC‐SIGN could be an efficient target for antibody‐mediated delivery of T cell epitopes in vaccine development. [ABSTRACT FROM PUBLISHER]

SUMMARY Insufficient stimulatory capacities of autologous dendritic cells (DC) may contribute in part to impaired T cell stimulation and therefore viral persistence in patients with chronic hepatitis B virus (HBV) infection. In order to characterize the antigen presenting functions of DC from chronic HBV carriers and controls antigen specific T cell responses were analysed. CD34+ peripheral blood progenitor cells were differentiated to immature DC in the presence of GM-CSF, IL-6/IL-6R fusion protein and stem cell factor. Proliferative CD4+ T cell responses and specific cytokine release were analysed in co-cultures of DC pulsed with HBV surface and core antigens or tetanus toxoid and autologous CD4+ T cells. Cultured under identical conditions DC from chronic HBV carriers, individuals with acute resolved hepatitis B and healthy controls expressed similar phenotypical markers but chronic HBV carriers showed less frequent and weaker HBV antigen specific proliferative T helper cell responses and secreted less interferon-γ while responses to the tetanus toxoid control antigen was not affected. Preincubation with recombinant IL-12 enhanced the HBV specific immune reactivities in chronic HBV patients and controls. In conclusion, the weak antiviral immune responses observed in chronic hepatitis B may result in part from insufficient T cell stimulating capacities of DC. Immunostimulation by IL-12 restored the HBV antigen specific T cell responses and could have some therapeutical benefit to overcome viral persistence. [ABSTRACT FROM AUTHOR]

Chimeric proteins containing antigen linked to cytokines have shown some promise as vaccine candidates but little is known of their mechanism of action, particularly at the level of the antigen-presenting cell. We have investigated this using a chimeric protein in which an immunodominant T cell epitope from influenza hemagglutinin peptide (HA), recognized in the context of I-Ed, was fused to IL-2. Immature murine dendritic cells (DC) derived from bone marrow (BMDC) were used to present the chimeric protein to a T cell hybridoma with TCR specific for the HA peptide (A5 cell line). HA–IL-2 was found to induce significantly higher T cell activation than HA alone. Although the inclusion of IL-2 and HA separately did increase the response of A5 cells compared to HA alone, they were not as effective as the HA–IL-2 chimeric protein. When an antibody known to block IL-2 receptor α chain (CD25) was included, A5 activation was reduced, suggesting a role for the receptor in this process. Expression of CD25 on A5 cells was low during activation, implying that the effect was mediated by CD25+ BMDC. Antigen uptake and processing of HA–IL-2 by BMDC was required since fixing BMDC, prior to antigen exposure, greatly reduced their ability to activate A5 cells. The function of CD25 on DC is currently unknown. Our results suggest this receptor may play a role in antigen uptake and subsequent T cell activation by receptor-mediated endocytosis of antigen attached to IL-2. This finding that may have implications for the development of a new generation of vaccines. [ABSTRACT FROM PUBLISHER]

One of the main limitations of using synthetic peptides for immunotherapy in allergic patients is the difficulty to delineate the immunodominant T cell epitopes which are necessarily dependent on HLA molecules. We have thus addressed the question of the role of MHC II molecules in immunodominant epitopes selection in the particular case of the major bee venom allergen (API m1). To exhaustively and easily explore it, we used BALB/c mice whose H-2 haplotype is associated with high IgE and IgG responses to API m1. By means of extensive sets of synthetic peptides, we investigated the specificity of polyclonal T cells and monoclonal hybridomas from mice immunized with API m1 and delineated four immunodominant regions, restricted to either the I-Ed or the I-Ad molecule. All the peptides were also tested for their capacity to bind to immunopurified MHC II molecules. Eight determinants of high affinity were identified. They clustered into three distinct regions and were largely overlapping. They included all the immunodominant epitopes, but half of them were not capable of stimulating T cells. Strikingly, interacting surfaces with either the TCR or MHC II molecule greatly differed from one determinant to another. In one case, we observed that flanking regions exerted a particular action on T cell stimulation which prevented the fine epitope localization. Our results underline the diversity and complexity of MHC II-restricted determinants and T cell epitopes from the major bee venom allergen, even in a single haplotype. These data also participate in the development of alternative approaches to conventional immunotherapy. [ABSTRACT FROM PUBLISHER]

Two tumour cell clones, 6D1 and 4C2 cells, which are defective both in the major histocompatibility gene complex (MHC) class I expression and in the endogenous antigen presentation, are recovered with interferon (IFN)-γ treatment. The present study describes the ultrastructure of these cells by using scanning and transmission electron microscopy in relation to the effect of IFN-γ treatment. The general morphology of these cells was found to be similar to each other and comparable to that of a tumour cell clone, 4A1 cells, of the same origin, normal in MHC class I expression; they exhibited a fibroblast-like appearance and had many blebs on all the cell surfaces, with desmosome-like junctions between cells. On EFN-γ treatment, surface fine blebs appeared less, and mitochondria became more densely stained. Expression of MHC class I molecules on the cell surface was much higher in the EFN-γ treated 6D1 and 4C2 cells than in untreated cells, when estimated by immunoelectron microscopy. The addition of an epitope peptide to these cells did not enhance the class I expression, which differed from other antigen presentation-defective cells such as RMA-S cells, nor change the cell surface morphology. [ABSTRACT FROM AUTHOR]

Evidence incriminating T cells in rheumatoid arthritis (RA) is strong but circumstantial - like a smoking gun at the scene of a crime. To investigate this, T lymphocytes were studied in health and disease. The effects of mutations in the groove of HLA-A2 on peptide presentation to T cells was studied to investigate normal T cell function. This allowed a detailed description of the interaction between individual MHC residues and antigens. Subsequently, T cells in the autoimmune disease, multiple sclerosis, were studied, to investigate the mechanisms for breakdown in peripheral tolerance. T-cell clones that recognized both autoantigens and viral proteins were isolated, suggesting that infection may trigger disease. Autoantigens would need to be defined to use this strategy in RA. T-cell responses to type II collagen, a candidate auto-antigen, were therefore studied in RA and an epitope successfully defined. The search for microbial 'mimics' triggering RA, and novel forms of immunotherapy are now possible - with potential rehabilitation of T cells. [ABSTRACT FROM PUBLISHER]

Dendritic cells (DC) were purified from human peripheral blood using a rapid and simple method based on magnetic depletion of phagocytes with carbonyl iron, followed by centrifugation of nonphagocytic cells on a Percoll density gradient and depletion of lymphocytes and macrophages/monocytes with a panel of MoAbs and immunomagnetic beads. Enriched DC were obtained with < 99% purity as judged by non-specific esterase (NSE) staining. After isolation, these cells, representing 0.4% of the starting mononuclear cell population, still function as potent antigen-presenting cells for purified T lymphocytes. The present results confirm the ability of human peripheral blood DC lo present soluble antigens to T cells including microbial antigens and show, further, that DC arc more potent soluble antigen-presenting cells than monocytes. The method was successfully applied to the purification of DC from the blood or HIV-infected individuals. We could not detect decreased numbers of DC in four individuals with early HIV infection and no replicating HIV was detected by in situ hybridization in the DC. [ABSTRACT FROM AUTHOR]

The difference between newborn and adult mononuclear cells in the antigen dose required for optimal antibody production in vitro can be ascribed to differences in the antigen-presenting capacities of the respective monocytes (Van Tol et al ., 1984b). We have therefore studied the expression of cell surface determinants on human neonatal and adult monocytes by the use of monoclonal antibodies to membrane proteins including MHC antigens. No difference was observed in the expression of LeuM3 with regard to both the percentage of positive cells and the density of the respective determinant. In contrast, neonatal cells express the antigens OKM5, LFA1, OKM1 and LeuM5 at a lower density than adult cells do. The same holds for β2-microglobulin, but neonatal and adult monocytes express MHC class I α-chains at a similar density, whereas among the class II MHC antigens, HLA-DR is significantly more highly expressed on neonatal cells. This difference remains after treatment in vitro with γ-interferon (γ-IFN). Treatment with γ-IFN also resulted in a less dense expression of the LeuM3 antigen. Preincubation of monocytes with LeuM3 monoclonal antibody partially abrogates subsequent upregulation of class II MHC antigens by γ-IFN, a phenomenon observed with both neonatal and adult monocytes. These data indicate a functional involvement or LeuM3 with the cellular action of γ-IFN. Taken together, the cell surface phenotype of neonatal monocytes is that of a highly efficient antigen presenting cell. [ABSTRACT FROM AUTHOR]

The helper function of human T4+ cells acting on autologous peripheral blood B cells was elicited by the hapten-carrier conjugate DNP-streptococcal antigen (DNP-SA), in the presence of monocyte-enriched cells. The antigen presenting function of monocyte enriched cells can be replaced by a subset of autologous T8+ Vicia villosa lectin adherent (T8VV+) cells. Cell depiction studies confirmed that the T8VV+ cell presentation was mediated by a T cell since killing with anti-T3 antibody and complement removed the antigen presenting capacity of T8VV+ cells but not of monocyte-enriched cells. Furthermore, killing with anti-la specific monoclonal antibody and complement abrogates antigen presentation by the T8VV+ cells, suggesting that the latter express an Ia gene product, The antigen presentation is specific to DNP-SA which elicits anti-DNP IgM antibodies, as the latter are not produced in response to tetanus toxoid. We suggest that interactions between T cells may occur not only by T8+ cells inducing T8+ suppressor cell functions but also the reverse activity of T8+ cell presenting antigen to T4+ cells to induce helper function in the absence of other accessory cells. [ABSTRACT FROM AUTHOR]

Interactions of human T cells and macrophages/monocytes (MØs) following stimulation by a Gram negative micro-organism (E. coli) have been investigated. Immunoadsorption studies showed that the E. coli-induced proliferative response of human T cells was antigen specific. The T cell pool could be selectively depleted of E. coli reactive cells by short exposure to autologous E. coli pulsed Møs, This treatment did not remove T cell reactivity directed towards an unrelated antigen (tetanus toxoid). This demonstrated the antigen specificity of the immunoadsorption step, which was further confirmed by reconstitution of E. coli reactivity after supplementing the adsorbed T cell pool with E. coli specific T cells. The MØ requirement for the E. coli-induced T cell response was confirmed and kinetic studies showed a dose-dependence with respect to the amount of E. coli used for both E. coli-induced T cell proliferation and the efficiency of immunoadsorption. [ABSTRACT FROM AUTHOR]

We have compared the capacity of dendritic cells (DC) and B cells to present peptide–class II complexes following administration of protein in adjuvant or in soluble form. Three different antigen-presenting cell (APC) populations were separated from draining lymph node cells from mice immunized s.c. with hen egg-white lysozyme (HEL) in adjuvant or with adjuvant only followed by soluble HEL: DC (N418+, class II+, B220-, low buoyant density), large B cells (B220+, low buoyant density) and small B cells (B220+, high buoyant density). HEL peptide–class II complexes displayed by these APC were evaluated by their capacity to activate HEL-specific T hybridoma cells. Following immunization with HEL in adjuvant, DC are the only lymph node APC population expressing detectable HEL peptide–class II complexes. Conversely, after i.v. administration of soluble HEL in mice previously injected with adjuvant only, lymph node B cells are much more efficient than DC in presenting peptide–class II complexes to T cells. Therefore, different modes of protein antigen administration lead to selective expression of antigenic complexes by different APC populations. These data correlate with the observation that, unlike B cells, DC recruited in lymph nodes of mice injected with adjuvant only present in vitro processed protein antigen much less efficiently than synthetic peptides, probably as a consequence of their maturation in vivo. [ABSTRACT FROM AUTHOR]

P18IIIB is a highly immunogenic peptide from the V3 loop of the HIV-1 gp160 envelope protein that is presented promiscuously by multiple class I MHC molecules. Understanding the molecular basis for promiscuous presentation may have many practical applications. As the highly prevalent HLA-A2.1 class I molecule is known to present P18IIIB for recognition by cytotoxic T lymphocytes (CTL) found in peripheral blood mononuclear cells of HIV+ donors, a P18III-specific CTL line was generated from an HLA-A2+, HIV- donor in order to define the molecular basis for, and ultimately improve upon the binding of, this peptide to HLA-A2.1. The minimal epitope recognized by the line was a decamer,I10, with the sequence RGPGRAFVTI. Interestingly, this decamer is identical to the minimal epitope from P18IIIB seen by murine CTL restricted by H-2Dd. A panel of Ala-substituted peptides was employed in MHC-binding and T cell response studies to identify MHC- and TCR-binding residues. Notably, many of the agretopic and epitopic residues identified were identical to those involved in the corresponding interactions of l10 with the H-2Dd MHC molecule and murine l10-specific CTL. The l10 peptide does not contain the described HLA-A2.1 binding motif. Instead a Pro at P3, a Phe at P7 and an Me at P10 are utilized for MHC binding. Agretopic residue similarities with the hepatitis B nucleocapsid decamer suggest that these residues may comprise an alternative motif of anchors utilized by decamers for binding to HLA-A2.1. [ABSTRACT FROM AUTHOR]

The successful induction of class I restricted cytotoxic T lymphocytes (CTL) responses with soluble non-replicating antigens relies upon vehicles which deliver antigen appropriately to antigen presenting cells (APC), which for CTL may be dendritic cells (DC). In this study, we have followed the distribution of liposomes and their incorporated antigen and compared the efficacy of splenic macrophages (Mø) and DC at inducing primary CTL responses . Our results show that whereas liposomes locate predominantly in the splenic red pulp and marginal zone locations, some of their soluble antigen contents redistribute to the central white pulp, comprising mainly DC and T cells. Such antigen redistribution was most apparent following administration of pH-sensitive liposomes. In comparisons of the APC activity of Mø and DC taken at various times post-Injection, DC were always superior to Mø. However, if Mø were depleted prior to antigen exposure, DC were ineffective APC for CTL induction. Furthermore, addition of supernatant from OVA-liposome treated Mø to naive DC-T cell cultures resulted in OVA-speclfic T cell responses. These studies indicate a role for Mø in enhancing the antigen presenting function of DC. [ABSTRACT FROM PUBLISHER]

We have previously described epltopes of the 18 kDa protein of which stimulate T and B cell responses in different strains of mice. A series of overlapping 20-mer peptides that span the 18 kDa protein were used as immunogens to examine T and B cell recognition of different epltopes. Strain-specific variation in the epltopes which induce the strongest responses was affected by genes linked to the H-2 complex and the T cell responses revealed by re-challenge with antigen were at least partially controlled by factors other than T cell specificity. We have examined the responses to one such antigen, peptlde 1–20, which contains strongly immunogenlc epltopes for T and B cells. T cells from draining lymph nodes of peptlde 1–20 immunized B10.BR, but not BALB/c mice, proliferated In response to rechallenge with peptlde 1–20 or whole protein. Immunization with the same peptlde also induced specific antibody only in B10.BR mice. However, Immunization of BALB/c mice results in ‘silent’ priming of T cells since these can be induced to respond to this antigen when cultured with activated macrophages as antigen presenting cells (APC). The failure of APC from mBALB/c mice primed with peptlde 1–20 to stimulate CD4 proliferation when re-challenged and the failure to elicit antibody responses to peptlde 1–20 are presumably due to the same defect in antigen-presenting cell function, since presentation of peptlde 1–20 by activated macrophages is sufficient to restore both responses. The failure of APC to stimulate responses to this antigen in this model may be generally applicable to other cases of apparent non-responsiveness, and may have important implications for the understanding of T cell activation requirements. [ABSTRACT FROM PUBLISHER]

C5, the fifth component of complement, Is a circulating self protein which induces complete tolerance in MHC class II restricted, CD4 T cells due to the presentation of C5 taken up from plasma. Functional recognition of processed C5 was monitored by activation of C5 specific T cell hybrids cultured with antigen presenting cells (APC) from C5 expressing mice. Dendritic cells Isolated from various tissues (spleen, thymus, skin) proved to be the most efficient APC, since 10-to 50-fold more macrophages and at least 100- to 500-fold more B cells were needed to achieve similar T cell activation. Stimulatory C5 peptide - class II complexes generated were retained on the surface of dendritic cells but not on macrophages and B cells upon prolonged culture: Dendritic cells but not macrophages from thymus presented processed C5. Taken together these findings emphasize the crucial role dendritic cells play for recognition of soluble self proteins by MHC class II restricted T cells. [ABSTRACT FROM PUBLISHER]

We have used different mouse strains to examine and responses to the 18 kDa protein of , which appears to be strongly immunogenic in both mice and humans. B and T cell stimulatory epitopes recognised by different strains of mice have been mapped using overlapping peptides that span the entire 18 kDa protein. Previous work established that Immunization of mice with the 18 kDa protein results in specific antibody production to common B cell epitopes and immunization of mice with peptides containing these B cell epitopes resulted in the induction of specific IgG to only a limited subset of epitopes in each strain. Now we report that T cells purified from mice immunized with peptides that stimulate antibody production, proliferate when rechallenged. The proliferating T cells produce levels of IL-2 and IFN-, that indicate antigen-specific T helper type 1 cells are present in significant numbers. Thus, a comparison of and data suggests that T cells bearing the phenotype associated with potentially protective cell-mediated responses can be primed by epitopes on small peptides. Since T cells from both strains of mice are capable of responding to the immunogenic synthetic peptides , but give different responses to the same peptides , factors other than epltope structure appear to influence T cell subset activation. This may have important implications for diseases such as leprosy where a polarized T cell response appears to develop and for the development of synthetic subunit vaccines. [ABSTRACT FROM PUBLISHER]

The study was undertaken to evaluate the relationship between non-responsiveness to hepatitis B (HBV) vaccination in haemodialysed patients and HBs antigen (Ag) presentation and recognition depending on TCR/CD3 receptors expression. We have found that the cause of the blunted response to HBV vaccination is multifactorial and seems to be associated with the following: (1) A reduced number of TCR/CD3 antigen receptor complexes on freshly isolated uraemic CD4 T cells, especially in non-responders. (2) The blunted proliferative response of uraemic CD4 T cells isolated from non-responders and stimulated for 6 days by autologous monocytes presenting HBsAg was associated with the decreased density of the TCR/CD3 receptors. (3) Moreover, in uraemic non-responders the expression of adhesion and accessory molecules on monocytes (intercellular adhesion molecule-1/ ICAM-1, HLA-DR/Ia/) was significantly decreased following the culture with autologous monocytes serving as HBsAg-presenting cells. CD4 molecules and lymphocyte function antigen-1β /LFA-1β/ on helper-inducer T cells were increased before and after the culture. (4) These findings were also associated with a diminished binding capacity of IL-1β and IL-6 to their receptors on helper-inducer T cells. (5) IL-2, IFN-γ and IL-4 production was decreased in uraemic non-responders, especially after 72 h of the culture. (6) Inhibited proliferation of helper-inducer T cells in uraemic non-responders was only partially reversible in the presence of exogenous IL-1β, IL-6, IL-2 and IFN-γ. (7) HLA typing of uraemic non-responders was associated with extended haplotype: HLA A1, B8, DR3, DR7, DQ2. [ABSTRACT FROM PUBLISHER]

MHC class II molecules are Involved in the presentation of both exogenous and endogenous antigens to CD4 T cells. Using the trans-membrane hemagglutinin (HA) from measles virus and the secreted hen egg lysozyme (HEL) as antigen models, we have compared the efficiency of MHC class II presentation by naive antigen presenting cells (APCs) pulsed with exogenous antigen with that of their transfected counterparts synthesizing endogenous antigen. B cells expressing even a very low amount of trans-membrane HA were found to present endogenous HA to I-E restricted T cell hybridomas with a high efficiency whereas their naive counterparts required to be pulsed with a comparatively high amount of exogenous HA. Similarly, MHC class II presentation of endogenous secreted HEL was found to be much more efficient when compared with that of exogenous HEL. Biochemical studies did not reveal any enhanced intracellular degradation of endogenous HEL. As expected, HEL was released in the surrounding medium within <1 h. MHC class II presentation of endogenous HEL could not be explained by re-uptake by bystander APCs of HEL secreted in the surrounding medium. No sensitization of naive APCs could be observed either when co-cultured with HEL secreting cells or when cultured for 10 days with a sub-threshold amount of exogenous HEL. At the cell surface, I-E molecules immunoprecipltated from HEL secreting cells were found to be slightly enriched In SDS-resistant forms. These data raised the question of how peptides derived from endogenous trans-membrane and secreted antigens can so efficiently reach an MHC class II loading compartment. [ABSTRACT FROM PUBLISHER]

We describe T560, a tissue culture-adapted B lymphoma derived from the gut-associated lymphoid tissue (GALT) of a (B10 × B10. H-2 H-4)F hybrid mouse. This lymphoma Is interesting and useful not only because it bears an unusual IgA receptor, fully described elsewhere, but also because It is potentially capable of presenting antigen to T cells restricted by the MHC of either parent. Here we document that T560 cells are lgG2aκ, la , B220, J11d.2 , CD3, CD4, CD5, Mac 1, Mac 2, non-specific esterase. They bind bromelain-treated mouse RBC (BrMRBC) in a PC chloride-inhibltable manner but do not bind SRBC, ox RBC (ORBC) or TNP-ORBC. Two lines, T560.1 and T560.2, and several clones are available. T560.1 and its clones contain low numbers of IgA rosette-forming cells (RFC), intermediate numbers of lgG2a RFC and moderately high numbers of lgG2b RFC; T560.2 and its clones contain moderately high numbers of IgA RFC and low numbers of both lgG2a and lgG2b RFC. Both lines stimulate both B10 and B10.A cells in mixed lymphocyte reactions (MLR) and present keyhole limpet hemocyanin (KLH) to KLH-reactive T cells. T560.2 populations are, however, more efficient possibly because they have somewhat higher proportions of brightly fluorescent la+ cells and secrete larger quantities of lymphokine than T560.1 cells. They present PC-conjugated KLH (PC-KLH) -20 times more efficiently than unconjugated KLH, suggesting that their PC binding receptors function in antigen uptake. They constitutively produce IL-1, IL-4 and IL-6, but not IL-2, IL-5 or TGFβ. Neither their IgA nor their IgG receptor expression is affected by IL-4 or by IFNs-α, -β, or -γ. In their ability to bind BrMRBC and secrete IL-4, they resemble the CH12 lymphoma but differ from it in that they are of F hybrid origin, are CD5, bear lgG2a rather than IgM, do not bind sheep erythrocytes and have a receptor for IgA not present on CH12. [ABSTRACT FROM PUBLISHER]

Human peripheral blood monocytes pretreated with human recombinant tumour necrosis factor alpha (rTNF) showed an enhanced ability to present a soluble antigen, a purified protein derivate of tuberculin, to autologous T lymphocytes as assessed by their increased proliferation . This enhancing activity was due to TNF and not impurities in TNF preparations as anti-TNF antibodies abolished this phenomenon. The rTNF-treated monocytes showed an increased expression of HLA-DR molecules and enhanced co-stimulatory activity in the murlne thymocyte assay. Pretreatment of monocytes before an antigen pulse with antl-TNF mAb Inhibited antigen presentation, which indicated that endogenously produced TNF was involved. These studies thus suggest that TNF acts in an autocrine fashion and enhances the ability of monocytes to present protein antigen. It is unclear at present whether this effect is due to the modification in antigen processing, expression of MHC class II molecules, or other factors (IL-1, IL-6, adhesion molecules, etc.) that are important for the Induction of T cell response to a nominal antigen. The enhancement of the antigen presenting capacity of monocytes/macrophages may be the additional mechanism of pro-inflammatory activity of TNF. [ABSTRACT FROM PUBLISHER]

Mice deficient for the fifth component of murine complement (C5), unlike normal mice, do not possess the secreted form of C5 in their body fluids and can be readily immunized to serum-derived normal C5. Although macrophages from C5-deficient mice do not secrete C5, they synthesize the precursor form (pro-C5). Therefore contact of T cells with autologous pro-C5 presented by macrophages is theoretically possible. We show that macrophages from C5-deficient mice can Indeed stimulate a class II restricted CS-specific T cell clone without addttion of exogenous C5. lmmunization of C5-deficient mice with autologous pro-C5 induces vigorous C5-specific T cell proliferation and pro-C5 is recognized by C5-specific T cells in , demonstrating that this protein fails to induce tolerance under physiological condltions. Thus, intraceliuiar pro-C5 is processed and presented by C5-deficient macrophages and can activate T cell clones , yet is neither immunogenic nor tolerogenic for T cells in . [ABSTRACT FROM PUBLISHER]