Inhibition of antigen-stimulated in vitro proliferation of thymic dependent chicken spleen cells by specific antibody

The ability of passively administered antibody to inhibit active immune responses suggests that antibody may be an important element in normal immunoregulation. This report describes studies of in vitro lymphocyte transformation in which cells from agammaglobulinemia bursectomized-irradiated (Bx-X) and rabbit anti-chicken lymphocyte serum (ALS)-treated chickens were used to study the effects of specific antibody on the in vitro proliferative responses of thymus dependent (T) and bursal dependent (B) lymphocytes. Intact chickens immunized with keyhole limpet hemocyanin (KLH) and Brucella abortus (BA) developed positive in vitro proliferative responses to these antigens and these responses were specifically inhibited when the appropriate antibody was added to the cultures. Low level “natural” or background proliferative responses were observed in unimmunized chickens in response to Brucella, and these responses could not be inhibited by specific anti-Brucella (anti-BA) antibody. Agammaglobulinemic (Bx-X) chickens immunized with both KLH and Brucella responded in vitro only to KLH. This response was also inhibitable by specific anti-KLH antibody, indicating that proliferative responses of T cells can be suppressed by specific antibody. Because spleen cells from immunized Bx-X birds failed to respond to Brucella, the in vitro proliferative response to this antigen is probably a B lymphocyte dependent process. This was investigated further by using spleens from immune ALS-treated chickens. These cells failed to respond to either antigen in vitro. When these ALS spleen cells were mixed with immune Bx-X spleen cells, the in vitro proliferative response to BA was reconstituted, demonstrating synergy between the two populations of cells. However, since both T and B cells are needed for the proliferative response to BA, we cannot determine which lymphoid cell was inhibited by anti-BA.