Ontogeny and immunohistochemical localization of thymus-dependent and thymus-independent RT6+ cells in the rat.

RT6 is a cell surface alloantigen that identifies a regulatory subset of peripheral T cells in the rat. Diabetes-prone BB rats are deficient in peripheral RT6+ T cells and develop spontaneous autoimmune insulin-dependent diabetes mellitus. Diabetes-resistant BB rats have normal numbers of RT6+ T cells, and insulin-dependent diabetes mellitus can be induced in these animals by in vivo depletion of peripheral RT6+ cells. Athymic rats are also severely deficient in peripheral RT6+ T cells. Although very different with respect to the peripheral RT6+ cell compartment, normal, athymic, and diabetes-prone BB rats all generate RT6+ intestinal epithelial lymphocytes (IELs). The goal of these studies was to analyze the ontogeny of RT6+ IELs and peripheral lymphoid cells by in situ immunohistochemistry. We observed the following. 1) RT6+ IELs appear before alpha(beta) T-cell-receptor- expressing IELs in diabetes-prone BB, diabetes-resistant BB, and athymic WAG rats. 2) In vivo depletion of peripheral RT6+ T cells in diabetes-resistant BB rats using a cytotoxic monoclonal antibody is not accompanied by depletion of RT6+ IELs. 3) A population of RT6+ T-cell-receptor-negative IELs is present in normal, euthymic diabetes-resistant BB rats, constitutes a larger percentage of the euthymic but lymphopenic diabetes-prone BB rat IEL population, and is the predominant IEL phenotype in athymic WAG rats. These results suggest that RT6+ cells are composed of both thymus-dependent and thymus-independent cell subsets that have different developmental characteristics and may differ in function.

Evidence that intrathymic islet transplantation does not prevent diabetes or subsequent islet graft destruction in RT6-depleted, diabetes-resistant BioBreeding/Worcester rats.

Pancreatic islet allografts transplanted intrathymically are accepted and restore normoglycemia in streptozotocin-diabetic rats given one injection of antilymphocyte serum. Intrathymic allografts similarly restore normoglycemia in diabetes-prone (DP) Bio-Breeding (BB) rats that have developed spontaneous autoimmune diabetes. Intrathymic islets also reduce the frequency of subsequent diabetes when transplanted prophylactically into young DP rats. These findings suggest that intrathymic transplantation can prevent not only allograft rejection, but also the appearance and recurrence of autoimmune tissue destruction. To explore these hypotheses further, we attempted both to confirm previous studies and to extend them to another model of autoimmune diabetes, the RT6-depleted diabetes-resistant (DR) BB rat. Fewer than 1% of DR-BB rats develop spontaneous diabetes, but most become hyperglycemic after in vivo immune elimination of RT6+ T cells. Using the protocols described in the literature, we observed the following: (1) Consistent with previous reports, intrathymic islet allografts survived indefinitely in streptozotocin-diabetic, antilymphocyte serum-treated, non-BB recipient rats. (2) Consistent with previous reports, intrathymic islet grafts produced long-term normoglycemia in diabetic DP-BB rats and also reduced the frequency of spontaneous diabetes in young animals transplanted prophylactically. (3) In contrast, intrathymic islets (iso- and allografts) neither prevented nor reversed diabetes in RT6-depleted DR rats. We hypothesize that intrathymic islet grafts survive in DP-BB rats because they are lymphopenic and immunocompromised, whereas immunocompetent diabetic DR rats successfully recapitulate the autoimmune disease process. Although intrathymic allograft transplantation is postulated to induce a state of tissue-specific tolerance, our results indicate that this tolerant state may not extend to autoimmune destruction of either isografts or allografts.

The RT6 rat lymphocyte alloantigen circulates in soluble form.

RT6 is a rat maturational lymphocyte alloantigen that appears to subserve important immunoregulatory functions. The lymphopenic diabetes-prone BioBreeding (BB)/Worcester rat is severely deficient in RT6+ T cells and develops spontaneous autoimmune diabetes mellitus. Transfusion of RT6+ T cells prevents the disease. Conversely, in vivo immune elimination of RT6+ T cells from the diabetes-resistant line of BB rats induces diabetes and thyroiditis. RT6 protein is expressed in two allotypic forms, each linked to the cell surface by a phosphatidylinositol (PI) anchor. The mechanism by which RT6+ T cells exert their regulatory function is not known, nor is the function of the RT6 protein defined. In this study, we investigated the possibility that, like other PI-linked proteins, RT6 also exists in a soluble form in the circulation. Using standard biochemical procedures we observed: (i) Soluble RT6 circulates in readily detectable amounts in all rat strains studied. (ii) The diabetes-prone BB rat circulates less RT6.1 than does any other strain, including the coisogenic diabetes-resistant line. (iii) Injections of monoclonal anti-RT6.1 antibody rapidly eliminate soluble RT6 from the circulation of diabetes resistant BB rats. The existence of a soluble form of a protein associated with immunoregulatory T cells suggests the possibility that soluble RT6 itself might possess immunomodulatory properties.

High stimulatory activity of dendritic cells from diabetes-prone BioBreeding/Worcester rats exposed to macrophage-derived factors.

Dendritic cells (DC) present antigen and initiate T cell-mediated immune responses. To investigate the possible association of autoimmunity with DC function, we compared the accessory activity of splenic DC from Wistar/Furth (WF) and diabetes-prone (DP) BioBreeding (BB) rats. The latter develop autoimmune diabetes and thyroiditis. DC function was quantified in vitro by measuring T cell proliferation in mitogen-stimulated and mixed lymphocyte reactions. When purified without macrophage coculture, WF and DP DC displayed similar levels of accessory activity. In contrast, when purified by a method involving coculture with macrophages, DC from DP rats consistently displayed greater accessory activity. This finding could not be explained by morphological or phenotypic differences between DP and WF DC. In accessory activity assays performed after reciprocal DC cocultures with DP and WF macrophages, DP DC exhibited higher accessory activity irrespective of macrophage donor strain. We also compared the accessory activity of WF and DP DC cultured in the presence of conditioned medium and a mixture of IL-1 and GM-CSF. In all assays, DP DC exhibited higher accessory activity. In studies of (WF x DP) F1 hybrids, the high accessory activity of DP DC was observed to be heritable, and studies of WF and DP radiation chimeras indicated that the effect was an intrinsic property of the DP hematopoietic system. We conclude: (a) splenic DC from DP and WF rats possess similar basal levels of accessory potency; (b) after interaction with macrophages, DC of DP origin are capable of greater stimulatory activity than are WF DC; and (c) the mechanism responsible for this phenomenon involves differential responsiveness of DP and WF DC to macrophage-derived factors such as IL-1 and GM-CSF.

An RT6a gene is transcribed and translated in lymphopenic diabetes-prone BB rats.

T-cells expressing the RT6 surface alloantigen appear to perform important immunoregulatory functions in the rat. Diabetes-prone BB rats lack circulating RT6+ T-cells and spontaneously develop autoimmune diabetes mellitus and thyroiditis. The coisogenic diabetes-resistant BB rat does circulate RT6+ T-cells and is free of disease. Transfusions leading to engraftment of RT6+ T-cells prevent both diabetes and thyroiditis in the diabetes-prone rat. To investigate the absence of this subset in the lymphopenic BB rat, we used both molecular and biochemical procedures and made the following observations: 1) an mRNA encoding RT6 protein is present in diabetes-prone spleen cells; 2) nucleotide sequencing of this transcript reveals an intact coding sequence for the RT6.1 alloantigen; 3) sensitive chemiluminescent assay of diabetes-prone lymph node cell detergent extracts shows that diabetes-prone RT6 mRNA is translated in vivo; 4) quantitatively, diabetes-prone lymph node cells express < or = 10% of the RT6.1 protein found on similar numbers of diabetes-resistant BB cells; and 5) finally, we obtained evidence of an intact phosphatidylinositol linkage of the molecule to the cell surface and successfully immunoprecipitated the phosphatidylinositol-linked protein with DS4.23 monoclonal antibody, indicating that the RT6.1 antigen is correctly processed and folded in diabetes-prone lymph node cells. We conclude that the near total absence of RT6+ T-cells in the diabetes-prone BB rat is unlikely to be because of a defect in RT6 gene expression per se. Defects in RT6 gene regulation or other cellular defects leading to premature cell death in the T-cell lineage, alone or in combination, may instead be responsible.

Induction of type I diabetes by Kilham's rat virus in diabetes-resistant BB/Wor rats.

Type I diabetes mellitus is an autoimmune disease resulting from the interaction of genetic and environmental factors. A virus that was identified serologically as Kilham's rat virus (KRV) was isolated from a spontaneously diabetic rat and reproducibly induced diabetes in naive diabetes-resistant (DR) BB/Wor rats. Viral antigen was not identified in pancreatic islet cells, and beta cell cytolysis was not observed until after the appearance of lymphocytic insulitis. KRV did not induce diabetes in major histocompatibility complex-concordant and discordant non-BB rats and did not accelerate diabetes in diabetes-prone BB/Wor rats unless the rats had been reconstituted with DR spleen cells. This model of diabetes may provide insight regarding the interaction of viruses and autoimmune disease [corrected]

Islet cells but not thyrocytes are susceptible to lysis by NK cells.

BB rats develop both pancreatic insulitis and lymphocytic thyroiditis, but whereas spontaneous autoimmune diabetes is common, hypothyroidism is rare. Splenic natural killer (NK) cells from acutely diabetic (AD) BB rats and from athymic nude rats are known to be cytotoxic to rat islet cells in vitro. To investigate possible differential tissue susceptibility to lysis by NK cells or their cytokines such as cytolysin (perforin) or NK cytotoxic factor (NKCF), we used an in vitro 51Cr-release assay to measure the cytotoxicity of splenocytes, cytolysin or NKCF against Wistar Furth (WF) and Fischer 344 (F-344) rat islet cells, and FRTL-5 F-344-derived and WRT Wistar-derived rat thyrocytes. The results demonstrated that spleen cells from AD-BB (RT1u) rats and athymic F-344 nude (RT11) rats are cytotoxic to WF (RT1u) islets and F-344 (RT11) islets, but not to FRTL-5 (RT11) or WRT (class I RT11) thyrocytes. WF and F-344 rat spleen cells were not cytotoxic to any of these cells. Thyrocytes are known to express class II molecules on their surface in chronic thyroiditis. We found that treatment of thyrocytes with interferon-gamma (IFN-gamma) induced class II expression but did not increase the cytotoxicity of splenocytes against these cells. Cytolysin and NKCF were both cytotoxic to islets in a dose dependent manner, but FRTL-5 thyrocytes were resistant to killing by these cytokines. These findings suggest that islet cells and thyrocytes in vitro are differentially susceptible to lysis by NK cells.

Recapitulation of normal and abnormal BB rat immune system development in scid mouse/rat lymphohemopoietic chimeras.

Mice homozygous for the mutation "severe combined immune deficiency" (C.B17-scid/scid) lack functional T and B lymphocytes and readily accept tumor xenografts. Partial lymphohemopoietic scid/human and mouse/rat chimeras have been described, but complete chimerization with thymic engraftment and generation of donor-origin thymocytes has not been achieved. We now report that low-dose irradiation permits the engraftment of BB rat fetal liver stem cells in scid recipients. We observed that BB rat fetal liver cells injected into irradiated scid mice establish a rat hemopoietic system in the scid mouse bone marrow and populate the scid mouse thymus. These stem cells generated rat-origin thymocytes that migrated to the scid mouse spleen, a peripheral lymphoid organ. Finally, we found that xenogeneic chimeras created using fetal liver cells from the abnormal (lymphopenic, diabetes prone) subline of BB rats recapitulated both the quantitative and phenotypic abnormalities of the donor rat. Xenogeneic lymphohemopoietic chimeras established in scid mice may provide a powerful new tool in the study of immune system development and autoimmunity.

Insulin treatment prevents diabetes mellitus but not thyroiditis in RT6-depleted diabetes resistant BB/Wor rats.

Prophylactic insulin administration is known to prevent hyperglycaemia in diabetes prone BB rats and non-obese diabetic mice. This study investigated the effect of insulin treatment on the development of overt diabetes, clinically inapparent anti-islet autoreactivity, and thyroiditis in RT6-depleted diabetes resistant BB rats. Fewer than 1% of these animals develop spontaneous diabetes, but if depleted of RT6- T cells greater than 50% become hyperglycaemic. We treated 30-day-old diabetes resistant rats with anti-RT6.1 monoclonal antibody, exogenous insulin, or both. Up to 60 days of age, 16 of 20 rats given antibody alone became diabetic, compared with 1 of 20 also treated with antibody plus insulin. Up to 110 days of age, only 1 of 10 rats treated with both insulin and antibody between 30 and 60 days became diabetic. Histologic study of non-diabetic insulin plus anti-RT6 antibody treated rats revealed insulitis in 3 of 9 at 60 days old, and insulitis in 3 of 8 and thyroiditis in 6 of 7 at 110 days of age. Non-diabetic animals were also found to harbour autoreactive spleen cells that adoptively transferred diabetes. Splenocytes from 60 or 110-day-old non-diabetic donors that had been treated with insulin and antibody between 30 and 60 days of age induced diabetes in 7 of 13 and 6 of 8 adoptive recipients respectively. We conclude that insulin treatment prevents clinical diabetes in the RT6-depleted diabetes resistant BB rat, but this treatment does not prevent the development of autoreactive cell populations that cause thyroiditis and adoptively transfer diabetes.

T-lymphocyte requirement for diabetes in RT6-depleted diabetes-resistant BB rats.

Diabetes-prone (DP) BB rats develop spontaneous autoimmune insulin-dependent diabetes mellitus (IDDM). The cell populations involved in the expression of diabetes are not precisely known but probably include natural killer (NK) cells, macrophages, and T lymphocytes. Because the DP rat has few lymphocytes of the CD5+/CD+ phenotype, cytotoxic T lymphocytes (Tc) are not believed to be important in the process. Diabetes-resistant (DR) BB rats that are depleted of RT6+ T lymphocytes also become diabetic and provide an additional model of IDDM. We report that diabetes in DR rats depleted of RT6+ T lymphocytes is prevented by the concomitant depletion of either the CD5+ or the CD8+ population. In contrast, coadministration of anti-asialogangliosideM1 (alpha-ASGM1), an antiserum that principally recognizes NK cells, failed to prevent hyperglycemia in RT6-depleted rats. We propose that the initiation of diabetes in both DP and RT6-depleted DR rats is T-lymphocyte dependent. However, the final common pathway leading to autoimmune beta-cell destruction in IDDM may be different in these models. The RT6-depleted DR rat requires a cell that is sensitive to anti-CD8 (possibly a Tc), whereas the DP rat requires an anti-ASGM1-sensitive cell.

Altered expression of diabetes in BB/Wor rats by exposure to viral pathogens.

Autoimmune diabetes mellitus affects greater than 50% of diabetes-prone BB (DP BB) rats but less than 1% of diabetes-resistant BB (DR BB) rats. We report an outbreak of spontaneous diabetes among DR BB rats that coincided with serologic evidence of the onset of viral infection. This apparent link between a change in the environment and the expression of diabetes then led us to study the interaction of environmental exposure to viral pathogens in this disorder with virally seropositive and seronegative populations of BB rats and polyinosinic-polycytidylic acid (poly I:C), an interferon inducer known to accelerate diabetes onset in DP rats. We administered a cytotoxic anti-RT6 monoclonal antibody, poly I:C, or both to DR rats. Depletion of the RT6.1+T-lymphocyte population has previously been shown to induce diabetes and thyroiditis in DR rats. RT6 alone did not induce diabetes in seronegative DR rats, and poly I:C was only weakly effective, but nearly all animals given both reagents became diabetic. When given to seropositive DR rats, either reagent alone induced diabetes; when given to non-BB rats, neither agent was effective. Poly I:C also accelerated the onset of DP diabetes to a greater extent in seropositive than in seronegative rats. We conclude that expression of the genetic predisposition to diabetes present in all BB rats depends on cellular factors that include the presence or absence of regulatory (RT6+) T lymphocytes and modulatory environmental factors including exposure to viral pathogens.

Immunopathology of diabetes in the RT6-depleted diabetes-resistant BB/Wor rat.

Insulin-dependent diabetes mellitus appears to be an autoimmune disease that is characterized morphologically by insulitis, an inflammation of the pancreatic islets of Langerhans that results in the destruction of the insulin-producing beta cells. The RT6-depleted DR rat provides a good model for the in situ study of insulitis. The authors used the anti-RT6.1 monoclonal antibody to selectively deplete RT6 T cells in DR rats and produce a synchronous and rapid development of insulitis that commences 10 days after treatment. The phenotype of cells that infiltrated the islets at different stages of insulitis in the RT6-depleted DR rat was determined by immunocytochemical techniques. A prodromal period of 10 days was present in which the authors could not detect morphologic alterations within the pancreas. This is followed by a second phase of early insulitis in which a few islets are infiltrated by macrophages and T cells. This rapidly progresses by 18 days to the final phase of generalized insulitis in which the islets are massively infiltrated by macrophages and T cells.

Adoptive transfer of autoimmune diabetes and thyroiditis to athymic rats.

We describe the induction of autoimmune diabetes, insulitis, and thyroiditis in athymic rats following injections of major histocompatibility complex compatible spleen cells. Lymphocytes with these capabilities were found in normal rats of the YOS, WAG, PVG, and diabetes-resistant BB strains, and in diabetes-prone BB rats. Adoptive transfer was facilitated by prior in vivo depletion of RT6.1+ regulatory T cells and in vitro mitogen activation of donor spleen cells. By RT6 depleting diabetes-resistant donors and using nude recipients, transfer of diabetes and thyroiditis was accomplished by using fresh, unstimulated spleen cells. The data suggest that organ-specific autoreactive cells may be present to various degrees but suppressed to a variable extent in many rat strains. The equilibrium between autoreactive and regulatory cells appears to determine the expression of autoimmunity.

Biochemical studies of RT6 alloantigens in BB/Wor and normal rats. Evidence for intact unexpressed RT6a structural gene in diabetes-prone BB rats.

Lymphocytes bearing the T-lymphocyte differentiation antigen RT6 play an important immunoregulatory role in the development of autoimmune diabetes in BB rats. Immunofluorescence studies suggest that diabetes-prone (DP)- but not diabetes-resistant (DR)-BB rat lymphocytes fail to express RT6 antigen during ontogeny. Two alloantigenic forms of the molecule exist, i.e., RT6.1 and RT6.2; both are linked to cell membranes by a phosphatidylinositol (PI) linkage. In these studies, PI-phospholipase C (PLC) treatment of lymphocytes from BB and normal rats followed by immunoabsorption and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of released proteins with anti-RT6 allotype-specific monoclonal antibodies was performed. RT6.1 in several nondiabetic rat strains was found to consist of a family of nonglycosylated and variably glycosylated molecules: an N-Glycanase-resistant 24,000- to 26,000-Mr peptide and four N-Glycanase-sensitive peptides of 29,000, 31,000, 33,000, and 34,000 Mr. In contrast, RT6.2 was found to be a 24,000- to 26,000-Mr nonglycosylated polypeptide. The electrophoretic pattern of RT6.1 was observed to be the same when the antigen was extracted from W3/25+ (CD4+) versus W3/25- T lymphocytes or from resting versus mitogen-activated cells. A pattern of bands characteristic of the RT6.1 antigen found in normal rat strains was detected after PLC treatment or detergent solubilization of lymphocytes obtained from DR rats. In contrast, no evidence of either RT6 species was found after PLC or detergent treatment of comparable numbers of T lymphocytes from DP-BB rats. Interestingly, T lymphocytes from Wistar-Furth (RT6.2+) x DP (RT6-) F1 crosses were observed to coexpress both RT6.2 and RT6.1 molecules, with the electrophoretic pattern of RT6.1 being similar to that obtained in DR and other rat strains. This study provides biochemical evidence that DP rats may have an intact RT6a structural gene.

Intrinsic cytotoxicity of natural killer cells to pancreatic islets in vitro.

BB rats develop spontaneous autoimmune insulin-dependent diabetes mellitus that is similar to human insulin-dependent diabetes. In this study, we used an in vitro islet cell cytotoxicity assay to study the possible role of natural killer (NK) cells and their soluble effector molecules in this disorder. First, the results demonstrated that in vivo treatment of acutely diabetic BB rats with anti-asialogangliosideM1 (an NK cell antiserum) but not with anti-T-lymphocyte antibodies reduces spleen cell cytotoxic activity to islets in vitro. Flow microfluorometry (FMF)-sorting experiments were then used to confirm that the splenic cytotoxic effector cell in acutely diabetic BB rats is a CD8+/CD5- NK cell. Further analysis demonstrated that both FMF-sorted NK cell populations from Wistar-Furth rats and unfractionated spleen cells from athymic nu/nu rats with high intrinsic NK cell activity also exhibit high islet cell cytotoxic activity in vitro. Finally, we found that the kinetics and differential cytotoxic activity of NK cells toward islets in vitro could be mimicked by NK cell culture supernatants containing high levels of NK cytotoxic factor (NKCF). The islet cytotoxic activity of these culture supernatants was specifically inhibited by the addition of anti-NKCF monoclonal antibody. These results demonstrate that NK cells from diabetic and nondiabetic rats are cytotoxic to islet cells in vitro. They further suggest that this cytotoxic effect may be mediated in part through the production and release of soluble factors such as NKCF.

The effect of ciamexone on lymphocytic thyroiditis and insulin-dependent diabetes mellitus in the BB/Wor rat.

Previous studies have suggested that ciamexone, a 2-cyan-aziridine derivative, is a selective immunomodulatory agent with potential therapeutic application in a variety of autoimmune diseases. In the present study, the effects of ciamexone on autoimmune lymphocytic thyroiditis and diabetes mellitus were studied in the BB rat. The data suggest that, in this animal model, ciamexone does not affect the frequency of autoimmune diabetes or lymphocytic thyroiditis nor does it affect the serum TSH or T4 concentrations.

Autoimmune destruction of islets transplanted into RT6-depleted diabetes-resistant BB/Wor rats.

We report a novel animal model of islet transplantation that distinguishes recurrence of autoimmunity from allograft rejection. In this study, diabetes-resistant (DR) BB rats, less than 1% of which develop spontaneous diabetes, were made hyperglycemic by either a single injection of streptozocin (STZ) or in vivo immune elimination of a regulatory T-lymphocyte subset that expresses the RT6 alloantigen. DR islet grafts were then transplanted into both groups. DR transplants into STZ-induced diabetic DR rats produced long-term normoglycemia. In contrast, DR transplants into DR rats that had been treated with anti-RT6 monoclonal antibody were all destroyed within an average of 4 days. Allogeneic islets transplanted into both STZ-induced and RT6-depleted diabetic DR rats were rejected within a mean of 3 days. We conclude that failure of DR islet grafts in RT6-depleted diabetic DR BB rats represents recurrent autoimmunity.

Prevention of diabetes in the BB rat by essential fatty acid deficiency. Relationship between physiological and biochemical changes.

Essential fatty acid (EFA) deficiency exerts a striking protective effect in several animal models of autoimmune disease. We now report that EFA deprivation prevents diabetes in the BB rat, an animal model of human insulin-dependent diabetes mellitus. In diabetes-prone (DP)-BB rats, the incidences of spontaneous diabetes and insulitis (the pathological substrate of autoimmune diabetes) were greatly reduced by EFA deficiency. This beneficial effect of the deficiency state was also seen in diabetes-resistant (DR)-BB rats that, after treatment with antibody to eliminate RT6+ T cells, would otherwise have become diabetic. The susceptibility of EFA-deprived DP-BB rats to spontaneous diabetes was restored when they were given dietary supplements of linoleate at 70 d of age (during the usual period of susceptibility), but not when they were repleted beginning at 120 d (after the peak incidence of diabetes). EFA deficiency did lead to growth retardation, but calorically restricted control rats demonstrated that the protective effect of the deficiency state was not a function of decreased weight. To examine the relationship between the biochemical changes of EFA deficiency and its physiological effects in this system, we compared the fatty acid changes that occurred in EFA-deficient animals that did and did not develop diabetes. Nondiabetic animals had significantly lower levels of (n-6) fatty acids (i.e., linoleate and arachidonate) and higher levels of oleate, an (n-9) fatty acid, than did diabetic animals. Levels of 20:3(n-9), the fatty acid that uniquely characterizes EFA deficiency, were similar in both groups, however. Among diabetic EFA-deficient rats, the age at onset of diabetes was found to correlate inversely with the level of (n-6) fatty acids, the least depleted animals becoming diabetic earliest, whereas there was no correlation with levels of 20:3(n-9). Among animals repleted with linoleate beginning at 70 d, restoration of susceptibility to diabetes correlated with normalization of the level of arachidonate. In summary, EFA deprivation reduced the frequency of diabetes in both DP and RT6-depleted DR-BB rats. This protective effect was strongly associated with depletion of (n-6) fatty acids, particularly arachidonate, but not with accumulation of the abnormal 20:3(n-9). Conjecturally, arachidonate and/or a metabolite may play a key role in mediating inflammatory injury in this animal model of autoimmune diabetes.