EXPRESSION OF THE CD28 COSTIMULATORY MOLECULE ON SUBSETS OF MURINE INTESTINAL INTRAEPITHELIAL LYMPHOCYTES CORRELATES WITH LINEAGE AND RESPONSIVENESS

The CD28 antigen has been recently demonstrated to be a costimulatory molecule and is expressed by almost all thymic and peripheral T cell r eceptor (TcR) alphabeta+ and gammadelta+ cells in the mouse system.We show here that expression of CD28 is heterogeneous among murine intest inal intraepithelial lymphocytes (IEL). Whereas some TcR alphabeta-exp ressing IEL subsets such as CD4+8- and CD4-8alpha+beta+ cells express CD28 at the same levels as their phenotypic counterparts in lymph node , other subsets of TcR alphabeta cells (including CD4-8alpha+beta- and CD4+8alpha+beta- cells) as well as TcR gammadelta+ IEL fail to expres s CD28. Parallel experiments using aged BALB/c-nu/nu mice indicated th at CD28 expression patterns among IEL are quite similar to those of no rmal BALB/c mice. Furthermore, forward light scatter analysis showed t hat CD28- cells are considerably larger than CD28+ cells in the gut, a lthough cycling cells were rare in both subsets. Finally CD28- cells i n the gut did not proliferate or produce IL-2 upon stimulation by anti -CD3 monoclonal antibodies (mAb) and phorbol 12-myristate 13-acetate, whereas CD28+ cells in the gut and lymph nodes responded to these stim uli. The response of the CD28+ cells was enhanced by anti-CD28 mAb. Th ese results suggest that CD28- IEL (CD4-8alpha+beta- cells, and some C D4+8alpha+beta- cells) may follow a different developmental pathway fr om that of CD28+ IEL in a thymus-independent environment, and that exp ression of CD28 correlates with responsiveness of the cells to trigger ing via the TcR-CD3 complex.