CENTRAL ROLE OF CD4+ T-CELLS IN AVIAN IMMUNE-RESPONSE

Chicken alphabeta T cells express either CD4 or CD8 accessory molecules, whereas most of the gammadelta T cells do not. The functional significance of the alphabeta T cells is relatively well understood. The CD4+ alphabeta T cells function as coordinators of the immune response, and CD8+ alphabeta T cells are the effector cells in cytotoxic responses, killing infected target cells. In comparison, the role of gammadelta T cells is so far poorly known. In chicken, the gammadelta T cells comprise a large lymphocyte subset. They can be induced to proliferate by various stimuli, but the proliferative response is dependent on CD4+ alphabeta T cells. The CD4+ T cells are also essential for the generation of antibody responses by providing help for the B cells and can influence cytotoxic responses as well. Thus, the CD4+ alphabeta T cells have a central role in the avian immune system, and their activation is a prerequisite for responses by other types of cells, including gammadelta T cells.