CD4(+)CD25(+) suppressor T (TS) cells play a critical role in the maintenance of peripheral tolerance. We examined here proliferative and functional responses as well as differential gene expression in T(S) cells. We found that T(S) cells were hyporesponsive to antigenic stimuli in vivo and unable to flux Ca(2+) upon T cell receptor (TCR) engagement. However, T(S) cells were not impaired in their proliferative response to lymphopenia, which was dependent on major histocompatibility complex class II expression. Homeostatic proliferation did not abolish T(S) cell anergy; rather, it substantially augmented T(S) cell function. DNA array analyses identified genes that may inhibit responsiveness at a number of levels in multiple signaling cascades in T(S) cells, as well as several anti-apoptotic genes that may mediate their survival.

Cathepsins have been implicated in the degradation of proteins destined for the MHC class II processing pathway and in the proteolytic removal of invariant chain (Ii), a critical regulator of MHC class II function. Mice lacking the lysosomal cysteine proteinase cathepsin S (catS) demonstrated a profound inhibition of Ii degradation in professional APC in vivo. A marked variation in the generation of MHC class II-bound Ii fragments and presentation of exogenous proteins was observed between B cells, dendritic cells, and macrophages lacking catS. CatS-deficient mice showed diminished susceptibility to collagen-induced arthritis, suggesting a potential therapeutic target for regulation of immune responsiveness.

Proliferative responses were performed as previously described. 10 Briefly, lymph nodes from OT-I mice were removed and single cell Immunology and Cell Biology (2000) Summary The present report provides the first extensive characterization of the OT-I TCR transgenic line, which produces MHC class I-restricted, ovalbumin-specific, CD8 + T cells (OT-I cells). These cells are shown to be positively selected in vivo in H-2 b C57BL/6 mice and in bm5 mice, which express the K bm5 mutant molecule. In contrast, OT-I cells were not selected by mutant K b molecules in bm1, bm3, bm8, bm10, bm11 or bm23 mice. Interestingly, however, when positive selection was examined in vitro in foetal thymic organ culture (FTOC), bm1 and bm8 were still poorly selective, but the bm3 haplotype now selected as efficiently as B6. The ability to select in vitro correlated with the capacity to present the ovalbumin (OVA) peptide to OT-I cells, as measured by induction of an OVA-specific proliferative response. These results suggest that a lower affinity TCR:MHC interaction may be necessary for positive selection in FTOC compared with selection in situ.