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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]

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]

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]

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]

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]

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]