Antibodies against a tumour-associated antigen in an AKR lymphoma conditioned to grow in BALB/c mice

An experimental model was used in which AKR lymphoma cells (L15) were conditioned to grow in BALB/c mice leading to tumour-bearing (progressor) and tumour-rejecting (regressor) animals. The behaviour of antibodies present in the sera of these animals was studied using as antigen L15 cells or a soluble tumour-associated antigen TEs. Both sera showed similar IIF and haemagglutinating activity. However differences were observed for the complement cytotoxicity assay. Regressor serum as well as a rabbit anti-tumour-associated antigen serum were strongly cytotoxic for the AKR lymphoma cells while progressor serum showed markedly lower activity. Specific antibodies against the tumour-associated antigen were purified. In both sera they were located mainly in IgG1 but also in IgG2. The purified antibodies agglutinated specifically sensitized sheep erythrocytes and reacted by indirect immunofluorescence with L15 cells but not with AKR thymocytes. It is suggested that two qualitatively different humoral immune responses are involved in the mechanisms leading to tumour enhancement or rejection.