2 SEPARATE MECHANISMS OF T-CELL CLONAL ANERGY TO MLS-1(A)

T cell tolerance to superantigen can be mediated by clonal anergy in w hich Ag-specific mature T cells are physically present but are not abl e to mount an immune response. We induced T cell unresponsiveness to m inor lymphocyte stimulations locus antigen (Mls)-1a in mice transgenic for TCR Vbeta8.1 in three different systems: 1) injection of Mls-1a s pleen cells, 2) mating with Mls-1a mice, and 3) bone marrow (BM) chime ras in which Mls-1a is present only on nonhematopoietic cells. CD4+8-V beta8.1+ cells from all these groups did not proliferate in response t o irradiated spleen cells from Mls-1a mice. We compared the response o f these cells by T cell/stimulator cell conjugate formation, Ca2+ mobi lization, and proliferation assays. The mechanisms underlying the unre sponsiveness of these T cells appear to differ. CD4+8-Vbeta8.1+ cells from Mls-1a spleen cell-injected mice mobilized cytoplasmic Ca2+ but p roliferated at a reduced level in response to cross-linking with anti- TCR mAb. However, these cells formed conjugates, mobilized Ca2+, and p roliferated in response to MlS-1a when activated B cells were used as stimulators, although they produced reduced levels of IL-2. In Mls-1a/ b Vbeta8.1 transgenic mice, a subset in CD4+8-Vbeta8.1+ cells did not mobilize cytoplasmic Ca2+ after TCR cross-linking. Their conjugate for mation, Ca2+ mobilization, or proliferation in response to Mls-1a on a ctivated B cells was undetectable. Finally, CD4+8-Vbeta8.1+ cells from the BM chimeras proliferated to TCR cross-linking at a partially redu ced level and formed conjugates, mobilized Ca2+, and proliferated in r esponse to Mls-1a on activated B cells. These features suggest that th e mechanisms underlying the maintenance of anergy in Mls-1a spleen cel l-injected mice are distinct from those in Mls-1a mice.