The immune response to primary moloney sarcoma virus tumors in BALB/C mice: Cellular and humoral activity of long‐term regressors

Adult BALB/c mice injected with Moloney sarcoma virus (MSV) developed local tumors at the site of inoculation which spontaneously regressed within 20–25 days after injection. Lymphocytes and sera from long‐term regressor animals were examined for their specific activities in vitro against Moloney leukemia virus (MLV) determined antigen (s). Specific activity against the MLV‐positive target cells by the lymphocytes from these animals was found to be dependent on the presence of B lymphocytes. In order to investigate some of the possible mechanisms of action of the immune B cells, sera, which were characterized by complement‐dependent cytotoxicity, immunofluorescence and virus neutralization, were tested for their ability to stimulate normal syngeneic lymphocytes to be active against the target cells. These antisera placed on the target cells were found to stimulate normal unfractionated or T deprived cells to reduce the target‐cell numbers. This effect was not found with normal T lymphocytes. Time‐course kinetics of this antibody‐dependent cell‐mediated activity in vitro were defined.