Thymus-specific serine protease controls autoreactive CD4 T cell development and autoimmune diabetes in mice

Abstract

Type 1 diabetes is a chronic autoimmune disease in which genetic predispositions affect the immune system, leading to a loss of T cell tolerance to β cells and consequent T cell-mediated destruction of insulin-producing islet cells. Genetic studies have suggested that PRSS16 is linked to a diabetes susceptibility locus of the extended HLA class I region in humans. PRSS16 encodes what we believe to be a novel protease, thymus-specific serine protease (TSSP), which shows predominant expression in thymic epithelial cells and is suspected to have a restricted role in the class II presentation pathway. Consistently, Tssp is necessary for the intrathymic selection of few class II-restricted T cell receptor specificities in B6 mice. To directly assess the role of Tssp in autoimmune diabetes, we generated Tssp-deficient (Tssp°) NOD mice. While remaining immunocompetent, Tssp° NOD mice were protected from diabetes and severe insulitis. Diabetes resistance of Tssp° NOD mice was a property of the CD4 T cell compartment that is acquired during thymic selection and correlated with an impaired selection of CD4 T cells specific for islet antigens. Hence, in the NOD mouse, Tssp is a critical regulator of diabetes development through the selection of the autoreactive CD4 T cell repertoire.

Central tolerance spares the private high‐avidity CD4+ T‐cell repertoire specific for an islet antigen in NOD mice

“…were backcrossed to NOD/LtJ for 20 generations and heterozygous mice were intercrossed to generate NOD Tssp°and NOD WT control lines. NODscid, and Tssp°NODscid have been described [9]. All experiments involving animals were performed in accordance with national and European regulations and the Institut National de la Santé et de la Recherche Médicale Eur.…”

“…To ensure that these different polymorphisms did not break tolerance to mS100β protein, we immunized NOD WT and NOD Tssp°with mS100β 1-15 peptide and analyzed their CD4 + T-cell recall responses to the same peptide. Both NOD WT and NOD Tssp°mice responded to mS100β [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] and, as observed upon protein immunization, NOD Tssp°mice were hyporesponsive showing, a 40% reduction (mean±SEM at 50μg/ml peptide; WT = 8.4±0.8 versus KO = 5.2±0.7) as compared to NOD WT control mice (Fig. 1D).…”

“…45: 1946-1956 Cellular immune response 1947 least in part, from defects in central tolerance mainly linked to defects in apoptosis induction [5][6][7][8]. Defects in central tolerance in the NOD mouse are however also linked to the adverse effect of the thymus specific serine protease (TSSP) on the presentation of some self-Ags by thymic stromal cells [9]. Hence we showed that lack of TSSP expression by thymic DC promoted the deletion of several islet-Ag specific CD4 + T cells and protected NOD mice from spontaneous autoimmune diabetes [9].…”

“…Defects in central tolerance in the NOD mouse are however also linked to the adverse effect of the thymus specific serine protease (TSSP) on the presentation of some self-Ags by thymic stromal cells [9]. Hence we showed that lack of TSSP expression by thymic DC promoted the deletion of several islet-Ag specific CD4 + T cells and protected NOD mice from spontaneous autoimmune diabetes [9]. This unique experimental system is therefore well suited to characterize the islet-reactive TCRαβ repertoire of CD4 + T cells that have escaped central tolerance in the NOD mice and determine how this repertoire is imprinted by reinforced negative selection in TSSP-deficient NOD mice.…”

“…When required, the hybridomas were FACS-sorted to select population with homogenous TCR and CD4 staining. 5×10 4 hybridomas were stimulated in the presence of 4-5×10 5 NOD splenocytes and graded dose of mS100β [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] . Twenty-four hours later, IL-2 production was measured using the IL2-dependent CTL.L cell line.…”