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Derailment of immune responses can lead to autoimmune type 1 diabetes, and this can be accelerated or even induced by local stress caused by inflammation or infection. Dendritic cells (DCs) shape both innate and adaptive immune responses. Here, we report on the responses of naturally occurring human myeloid BDCA1+ DCs towards differentially stressed pancreatic β cells. Our data show that BDCA1+ DCs in human pancreas-draining lymph node (pdLN) suspensions and blood-derived BDCA1+ DCs both effectively engulf β cells, thus mimicking physiological conditions. Upon uptake of enterovirus-infected, but not mock-infected cells, BDCA1+ DCs induced interferon (IFN)-α/β responses, co-stimulatory molecules and proinflammatory cytokines and chemokines. Notably, induction of stress in β cells by ultraviolet irradiation, culture in serum-free medium or cytokine-induced stress did not provoke strong DC activation, despite efficient phagocytosis. DC activation correlated with the amount of virus used to infect β cells and required RNA within virally infected cells. DCs encountering enterovirus-infected β cells, but not those incubated with mock-infected or stressed β cells, suppressed T helper type 2 (Th2) cytokines and variably induced IFN-γ in allogeneic mixed lymphocyte reaction (MLR). Thus, stressed β cells have little effect on human BDCA1+ DC activation and function, while enterovirus-infected β cells impact these cells significantly, which could help to explain their role in development of autoimmune diabetes in individuals at risk. [ABSTRACT FROM AUTHOR]

IDDM results from the destruction of pancreatic beta-cells by autoreactive T-cells that appear to avoid deletion early in development, possibly due to improper interaction with antigen-presenting cells (APCs) resident in the thymus or periphery. In the nonobese diabetic (NOD) mouse, there exists a defect in APC function characterized by its failure to fully mature upon stimulation. The NOD mouse thus provides an excellent model for the investigation of APC dysfunction and development and how these relate to the incidence of autoimmune diabetes. We initiated studies of APC function in the NOD mouse with respect to antigen processing and presentation, using a well-characterized antigen hen egg lysozyme (HEL) and comparing it with the closely related, major histocompatibility complex (MHC) (I-Ag7) identical, diabetes-resistant mouse strain NOR. Proliferation assays comparing NOD and NOR HEL-specific T-cells demonstrated that the T-cell proliferation response of the NOD mouse to both native and denatured forms of the antigen is lower than that of NOR. When crisscross proliferation experiments were conducted using purified T-cells and irradiated spleen cells as APCs from both strains, the results demonstrated that the defect in proliferation resided in the APC compartment of activation. The levels of intracellular glutathione (GSH) were compared in splenic macrophages from NOD and NOR mice; it was found that on antigenic stimulation, NOR macrophages produced significantly more intracellular GSH than did NOD macrophages, even under hyperglycemic (50 mmol/l glucose) conditions. The lower amount of GSH seen in the NOD may result in less efficient processing of antigen, and subsequently, lower levels of T-cell activation. [ABSTRACT FROM AUTHOR]

Recent studies demonstrated that engagement of cytotoxic T lymphocyte antigen 4 (CTLA-4)/(CD152) generates an inhibitory signal to T cells which arrests an on-going immune response. Since aberrant CD152 activity is thought to contribute to autoimmunity, we examined the effect of CD152-mediated inhibitory signals on the response to self and foreign antigens in autoimmune, diabetes-prone NOD and non-autoimmune BALB/c mice. The interaction of CD152 with its ligand B7 was prevented by treating the mice with anti-CD152 blocking antibody, before and following immunization of the mice with the self-antigen, syngeneic islet cells, or the foreign antigen, key-hole limpet hemocyanin (KLH). CD152 blockade in BALB/c mice stimulated a robust islet-specific T cell-mediated immune response compared to control antibody-treated mice. The augmentation of T cell responses in BALB/c mice was consistent with the role proposed for CD152 as a down-regulator of T cell activation responses. Furthermore, CD152 blockade unmasked islet cell specific autoreactive T cells in the non-autoimmune BALB/c mouse. Conversely, CD152 blockade in NOD mice failed to regulate islet-specific auto-reactive T cell responses. However, CD152 blockade enhanced the T cell response to the exogenous, foreign antigen KLH in both non-autoimmune BALB/c and autoimmune NOD mice. Collectively, these results suggest that there is not a global defect in CD152-mediated regulation of peripheral T cell immune responses in NOD autoimmune mice but rather, a defect specific to T cells recognizing self antigen., (Copyright 2000 Academic Press.)

A whole cell Renibacterium salmoninarum vaccine was developed using 37 degrees C heat treated cells that were subsequently formalin fixed; this treatment reduced bacterial hydrophobicity and cell associated p57. Coho salmon Oncorhynchus kisutch were immunized with the p57- vaccine by either a combination of intraperitoneal (i.p.) and intramuscular (i.m.) injections or per os. In the first experiment, i.p./i.m. vaccination of coho salmon with p57- cells in Freund's Incomplete Adjuvant (FIA) conferred a statistically significant increase in mean time to death after the salmon were i.p. challenged with 4.1 x 10(6) colony forming units (cfu) of R. salmoninarum. There was no significant difference in response between fish immunized with R. salmoninarum cell surface extract in FIA and those immunized with extracellular protein (ECP) concentrated from culture supernatant in FIA. The i.p. challenge dose resulted in complete mortality of all fish by Day 43. In a second experiment, fish were orally vaccinated with p57- R. salmoninarum cells encased in a pH protected, enteric-coated antigen microsphere (ECAM). Fish were bath challenged with 4.2 x 10(6) cfu ml-1 on Day 0 and sampled at time points of 0 (pre-challenge), 50, 90, or 150 d immersion challenge. Vaccine efficacy was determined by monitoring the elaboration of p57 in the kidneys of vaccinated and control fish. Fish vaccinated orally demonstrated a significantly lower concentration of p57 (p < 0.01) at Day 150 post challenge compared to fish receiving ECAMs alone. Fish receiving p57 cells without ECAM coating also showed a significantly lower p57 level (p < 0.03) versus control. In contrast, fish injected intraperitoneally with the p57- cells or fish fed p57+ R. salmoninarum cells in ECAMs demonstrated no significant difference (p > 0.05) versus controls. In summary, these studies suggest the preliminary efficacy of 37 degrees C treatment of R. salmoninarum cells as an oral bacterial kidney disease vaccine.

Renibacterium salmoninarum is a Gram-positive diplo-bacillus and the causative agent of bacterial kidney disease, a prevalent disease of salmonid fish. Virulent isolates of R. salmoninarum have a hydrophobic cell surface and express the 57-58 kDa protein (p57). Here we have investigated parameters which effect cell hydrophobicity and p57 degradation. Incubation of R. salmoninarum cells at 37 degrees C for > 4 h decreased cell surface hydrophobicity as measured by the salt aggregation assay, and decreased the amount of cell associated p57. Incubation of cells at lower temperatures (22, 17, 4 or -20 degrees C) for up to 16 h did not reduce hydrophobicity or the amount of cell associated p57. Both the loss of cell surface hydrophobicity and the degradation of p57 were inhibited by pre-incubation with the serine protease inhibitor phenylmethylsulfonyl fluoride (PMSF). Cell surface hydrophobicity was specifically reconstituted by incubation with extracellular protein (ECP) concentrated from culture supernatant and was correlated with the reassociation of p57 onto the bacterial cell surface as determined by western blot and total protein stain analyses. The ability of p57 to reassociate suggests that the bacterial cell surface is not irreversibly modified by the 37 degrees C treatment and that p57 contributes to the hydrophobic nature of R. salmoninarum. In summary, we describe parameters effecting the removal of the p57 virulence factor and suggest the utility of this modification for generating a whole cell vaccine against bacterial kidney disease.

To investigate host leukocytes recruited to the pancreas by diabetogenic T cells, we administered islet-specific CD4(+) T cell clones to 2-week-old nonobese diabetic (NOD) mice and examined the resulting pancreatic infiltrate by flow cytometry. Two different Vbeta4(+)CD4(+) T cell clones, BDC 2.5 and BDC 6.9, were found to recruit a heterogeneous T cell population as determined by staining with a panel of anti-TCR Vbeta monoclonal antibodies. The majority of the diabetes-initiating, Vbeta4(+) T cell clones migrated to the spleen whereas only 5-8% of the T cell population infiltrating the pancreas was Vbeta4(+). Anti-IL-2 receptor staining indicated that fewer than 10% of the total population of infiltrating lymphocytes within the pancreas were in a highly activated state. We have further found that normal splenic T cells from the NOD mouse proliferate poorly to IL-2 in vitro, yet secrete IFN-gamma in response to IL-2 stimulation. These results suggest that the recruited host T cells in our disease transfer system are not directly pathogenic but, rather, are responding to the small numbers of inflammatory T cell clones by providing cytokines that facilitate the disease process., (Copyright 1998 Academic Press.)

Bacterial kidney disease has consistently resisted attempts to control it by prophylactic immunisation. Although successful vaccines have been produced to a number of Gram-negative fish pathogens, the relatively simple method used in these cases have not been successful with Renibacterium salmoninarum. A more circumspect and thorough knowledge of the biological function of R. salmoninarum antigens must be obtained. Also required is a more precise understanding of the role of regional immunity in effective prophylaxis. Aspects of R. salmoninarum's biology provide a provocative challenge to the vaccinologist. Its residence in, and apparent commandeering of the macrophage, indicate that a vigorous cell-mediated response will probably be required to generate protective immunity. Its most biologically potent secreted product, p57, appears to be an aggressin. Further, p57 has the capability of frustrating immunoprophylaxis by either misdirecting the immune response, or by preventing its induction. Many immunization studies have used injection immunization and challenge protocols. It now appears that alternative routes of immunization which had been considered less protective (i.e. oral immunization) may not only be more efficacious, but may be the only route that does not lead to a misdirected and possibly pathological immune response. Also, the general reliance on serum antibodies as the only means to assess immunity is fraught with difficulties, particularly with pathogens such as R. salmoninarum. Recent advances in the analysis of cellular immunity will be a great aid in the design of future vaccines.