CHARACTERIZATION OF EXTRATHYMIC T-CELLS OF CHICKENS

The function of CD4(+) T cells in antibody production was examined by using T cell subset-depleted chickens. CD4- and CD8-depleted chickens, established by the combination of thymectomy and injection of T cell subset-specific monoclonal antibodies, were immunized with sheep red b lood cells (SRBC). Titers of anti-SRBC antibody produced in CD4-deplet ed chickens were lower than those in control chickens, while no differ ence in the antibody production was observed between CD8-depleted and control chickens. In chickens depleted of both CD4(+) and CD8(+) T cel ls, the recovery of T cells in the periphery was demonstrated starting 3 weeks after T cell depletion. Those T cells recovered in the periph ery predominantly expressed CD4 molecules. Although low titers of anti body against SRBC were detected in chickens depleted of both CD4(+) an d CD8(+) T cells, an increase of anti-SRBC antibody production was coi ncidentally observed with the recovery of CD4(+) T cells in the periph ery. These results suggest that CD4(+) T cells could differentiate in extrathymic environments in chickens, and have a helper function in an tibody production similar to that of intrathymic T cells. These extrat hymic T cells, however, showed a lower proliferative response to conca navalin A than intrathymic T cells, suggesting that these extrathymic T cells may have some properties distinct from intrathymic T cells.