FUNCTIONAL-ANALYSIS OF T-CELL ANTIGEN 4-1BB IN ACTIVATED INTESTINAL INTRAEPITHELIAL T-LYMPHOCYTES

The 4-1BB antigen has been recently demonstrated to be a 30 kDa induci ble T-cell antigen and is expressed on the cell surface of activated s plenic T cells and thymocytes. This novel T-cell antigen also associat es physically with the T cell-specific protein tyrosine kinase, p56(lc k). W, show here that the inducible T-cell antigen 4-1BB is expressed on activated intestinal intra-epithelial T lymphocytes (IEL). After ac tivation, or in the presence of IL-2, the activated IELs showed higher levels of 4-1BB. Functional studies revealed that the activated IELs triggered with anti-4-1BB monoclonal antibody could enhance the level of IEL cytotoxicity against anti-CD3-secreting hybridoma cells. Cross- linking of anti-4-1BB antibody also enhanced the proliferation of IELs . These results suggest that the inducible antigen 4-1BB has broad bio logical functions which not only play a role in activated splenic T ce lls and thymocytes but also in the mucosal immune system.