Evidence of a Two Step Apoptosis Mechanism in Mature Bovine Peripheral Blood Lymphocytes Treated With Dexamethasone

Glucocorticoids and other stress hormones have demonstrated effects on the humeral and cellular components of the immune system. Dexamethasone (Dex), a synthetic glucocorticoid, is used frequently for inflammatory management in both humans and animals. We have investigated the effects of Dex on the physiology and function of bovine peripheral blood lymphocytes and in two continuous murine T cell lines, one sensitive (LBRM) and one insensitive (EL4) to Dex. We have compared these cellular models to identify the effects of stress hormones in development of immune stasis. Our results identified changes in viability after long-term and short-term exposure to Dex, as well as specific changes in nuclear morphology and inhibition of cell proliferation. We observed that continuous exposure to Dex induced little change in the viability of PBL. However, short-term exposure to Dex, followed by further culture in unsupplemented medium, resulted in a significant loss of viability. These PBL also exhibited nuclear alterations, consistent with apoptosis, including DNA condensation and decreased fluorescence with the nucleic acid dye, acridine orange. Finally, the mitogenic response of Dex-treated PBL was depressed as compared to controls. Our studies have demonstrated that apoptosis of mature lymphocytes is a likely mechanism leading to immune suppression associated with stress and its products. Future research will entail understanding the roles of cytokine and membrane alterations m the PBL response to stress

Hypo-active variant of IL-2 and associated decreased T cell activation contribute to impaired apoptosis in autoimmune prone MRL mice

Apoptosis of activated lymphocytes is crucial to the maintenance of immune homeostasis and self-tolerance, as demonstrated by the well-known autoimmune MRL/pr mouse lacking the death receptor Fas. However, even MRL+/+ activated T cells have a resistance to Fas-mediated apoptosis as compared to T cells from the non-autoimmune FVB/N strain. To understand the molecular mechanisms underlying these strain differences, we studied biochemical characteristics of T cells upon activation. Compared to FVB/N T cells, MRL T cells under-expressed procaspase-3 but over-expressed FLIPL. In addition, up-regulation of Bcl-X-L, IL-2, and CD25 was diminished in MRL cells, suggesting inadequate T cell activation. Upon finding that MRL, like other autoimmune strains NOD and SJL, has a hypo-active variant of the IL-2 gene, we added wild-type murine recombinanat (mr)IL-2 during activation. Exogenous mrIL-2 restored MRL apoptosis to the level of FVB/N; in addition, expression of procaspase-3, and FLIPL, Bcl-X-L and CD25 was normalized. These results suggest that defective MRL T cell activation, in part due to hypo-active IL-2, underlies the impaired apoptosis of this strain. In addition, the hypo-active variant of IL-2 shared among autoimmune strains may, by causing diminished cell activation and cell death, predispose these strains to develop autoimmune disease.Y

Expression in transgenic mice of dominant interfering Fas mutations: A model for human autoimmune lymphoproliferative syndrome

Most humans with autoimmune lymphoproliferative syndrome (ALPS) carry heterozygous dominant mutations in one allele of the gene encoding Fas/APO-1/ CD95. ALPS patients, like Fas-deficient MRL lpr/lpr mice, have lymphoproliferation, autoimmunity, increased CD4(-)/CD8(-) T lymphocytes, and apoptosis defects. Consistent with the phenotypic variability of lpr/lpr mice of different background strains, human genetic studies indicate that a Fas mutation is insufficient to induce ALPS in all mutation carriers, To investigate the dominant function of human Fas mutations and the additional genetic factor(s) involved in the development of ALPS, we generated transgenic mice expressing, in addition to endogenous Fas, mouse Fas molecules bearing mutations in the intracellular death domain corresponding to mutations identified in ALPS patients. Transgenic mice developed mild features of ALPS, including hepatosplenomegaly, elevated proportions of lymphocytes in spleen and lymph nodes, apoptotic defects, and hepatic lymphocytic infiltrates. Therefore defective murine Fas proteins act in a dominant manner to impair apoptosis of activated lymphocytes and disrupt lymphocyte homeostasis, The influence of genetic background on phenotype was studied by comparing transgenic mice on FVB/N and (FVB/N x MRL) backgrounds with syngenetic control mice and with MRL and MRL lpr/lpr mice. While expression of transgenic mutant Fas contributed mainly to hepatosplenomegaly and accumulation of lymphocytes, MRL background genes played a major role in the production of autoantibodies and elevated serum immunoglobulin levels. Moreover, compared to FVB/N (+/+) mice, a substantial Fas-specific apoptotic defect was found in MRL (+/+) mice, suggesting a mechanism for the known tendency of this strain to develop autoimmunity. (C) 1999 Academic Press.N

Human adenylate kinase 2 deficiency causes a profound hematopoietic defect associated with sensorineural deafness.

Reticular dysgenesis is an autosomal recessive form of human severe combined immunodeficiency characterized by an early differentiation arrest in the myeloid lineage and impaired lymphoid maturation. In addition, affected newborns have bilateral sensorineural deafness. Here we identify biallelic mutations in AK2 (adenylate kinase 2) in seven individuals affected with reticular dysgenesis. These mutations result in absent or strongly decreased protein expression. We then demonstrate that restoration of AK2 expression in the bone marrow cells of individuals with reticular dysgenesis overcomes the neutrophil differentiation arrest, underlining its specific requirement in the development of a restricted set of hematopoietic lineages. Last, we establish that AK2 is specifically expressed in the stria vascularis region of the inner ear, which provides an explanation of the sensorineural deafness in these individuals. These results identify a previously unknown mechanism involved in regulation of hematopoietic cell differentiation and in one of the most severe human immunodeficiency syndromes.Journal ArticleResearch Support, N.I.H. IntramuralResearch Support, Non-U.S. Gov'tSCOPUS: ar.jinfo:eu-repo/semantics/publishe