SOLUBLE MHC-II PEPTIDE COMPLEXES INDUCE ANTIGEN-SPECIFIC APOPTOSIS INT-CELLS

Soluble major histocompatibility (MHC) class II molecules in associati on with antigenic peptide recognize T cell receptors (TCRs) on CD4(+) T cells, Such recognition of MHC II-peptide complexes by T cells in th e absence of costimulatory signals is known to induce T cell nonrespon siveness. The present study describes that recognition of TCRs by MHC class II-peptide complexes induces antigen-specific apoptosis in a T c ell clone independently of nonresponsiveness. Apoptosis was demonstrat ed in a murine T cell clone (4R3.9) restricted for IA(k) in associatio n with a peptide analog of myelin basic protein [MBP(1-14)A(4)]. A dos e- and time-dependent T cell death was observed upon incubation of 4R3 .9 T cells with purified IA(k)-MBP(1-14)A(4) complexes, The specificit y of T cell apoptosis was shown by incubating 4R3.9 T cells with irrel evant IA(s)-MBP(90-101) complexes. The DNA fragmentation as a result o f apoptosis was demonstrated by agarose gel electrophoresis and by pul sing T cells with BrdU followed by the detection of BrdU-labeled DNA f ragments using an antibody enzyme-linked immunosorbent assay, The expr ession level of two regulatory intracellular proteins, bcl-2 and bax i nvolved in apoptosis showed a decrease in bcl-2 and an increase in bar with time. Finally, the nuclear shrinkage and chromatin condensation, typical hallmark of apoptosis, have been demonstrated by transmission electron microscopy of complex-treated T cells, Since the T cell clon e (4R3.9) used in this study failed to show nonresponsiveness by IA(k) -MBP(1-14)A(4) complexes, our results suggest that apoptosis induced b y purified MHC class II-peptide complexes may involve distinct pathway s rather than T cell nonresponsiveness, Such antigen-specific apoptosi s may have significant clinical relevance in deleting autoreactive T c ells in various autoimmune diseases. (C) 1996 Academic Press, Inc.