Splenic alterations during mammary tumorigenesis: diverse effects on different immune parameters.

An evaluation of various parameters of the immune system was undertaken in Balb/c mice transplanted with a syngeneic mammary adenocarcinoma. Increasing tumor burdens resulted in a depression of some cell mediated immune functions. In contrast, an augmentation of humoral responses was observed in tumor-bearing mice. A defect in the immunoregulatory mechanism did not appear to be responsible for the elevated humoral response as revealed in suppressor cell experiments. However, flow cytometric analysis of T and B lymphocyte levels in the spleens of mice with mammary tumors indicated that the numbers of Thy 1.2 positive cells were greatly diminished while there was only a slight increase in the proportion of cells bearing surface immunoglobulin. These splenic alterations accompanying tumor growth might be responsible for the altered immune responses observed in tumor-bearing animals.