Thymus‐specific serine protease regulates positive selection of a subset of CD4⁺ thymocytes

Abstract

Thymus-specific serine protease (TSSP) was initially reported as a putative protease specifically expressed in the endosomal compartment of cortical thymic epithelial cells (cTEC). As such, TSSP is potentially involved in the presentation of the self-peptides that are bound to MHC class II molecules expressed at the cTEC surface and are involved in the positive selection of CD4 1 thymocytes. We tested this hypothesis by generating mutant mice deprived of Prss16, the gene encoding TSSP. TSSP-deficient mice produced normal numbers of T cells, despite a decrease in the percentage of cTEC expressing high surface levels of MHC class II. By using sensitive transgenic models expressing MHC class II-restricted TCR transgenes (Marilyn and OT-II), we showed that the absence of TSSP markedly impaired the selection of Marilyn and OT-II CD4 1 T cells. In contrast, selection of CD8 1 T cells expressing an MHC class I-restricted TCR transgene (OT-I) was unaffected. Therefore, TSSP is involved in the positive selection of some CD4 1 T lymphocytes and likely constitutes the first serine protease to play a function in the intrathymic presentation of self-peptides bound to MHC class II complexes.

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

“…Mice B6-Tssp°mice [13] 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].…”

“…TSSP is highly expressed by cortical thymic epithelial cells (cTEC) but also, at lower levels by thymic DC [9,[11][12][13]. Therefore, to assess the relative contribution of either stromal compartment to the hyporesponsiveness of NOD Tssp°mice to mS100β 1-15 we generated mixed bone marrow (BM) chimeras in which either the TEC or the APC compartment lacked TSSP expression.…”

“…Strikingly the (A/V)PSGGSNAKL CDR3α sequence was also widely used by NOD Tssp°hybridomas and, remarkably, some hybridomas from NOD WT and NOD Tssp°expressed the very same (6W05, 6W21 and 5K09, 5K22, 5K31) or extremely similar (5K02, 6K01 and 1W03, 6W06, and 6W19) TCRα and TCRβ rearrangements. Given that these specific aa sequences were not germline encoded, these clonotypes likely provide a proliferative advantage in response to mS100β [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] (Table 2 and Supporting Information Table 2). …”

“…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.…”

CCR7-mediated migration of developing thymocytes to the medulla is essential for negative selection to tissue-restricted antigens

“…Thymic microenvironments, consisting of various thymic stromal cells, sequentially support the development and selection of thymocytes. In the cortex, cortical thymic epithelial cells (cTECs) present a set of self-peptides, because cTECs express unique proteasomes containing ␤5t (1) and lysosomal proteases (2,3), and are autophagous (4). Immature CD4 ϩ CD8 ϩ [double positive (DP)] thymocytes that express the virgin repertoire of the T cell receptors (TCRs) are generated in the cortex and selected via interaction between the TCRs and the self-peptide/ MHC complexes expressed by cortical cells, including cTECs and hematopoietic cells (5).…”