Immunosuppressive activity associated with a reticulum cell sarcoma of aged mice

Aging BC3F1 hybrid mice frequently develop a reticulum cell sarcoma (RCS) causing marked hypercellularity of lymphoid tissues and pronounced suppression of humoral immunity. Cells of malignant spleens gave feeble responses in vitro to thymus-dependent and -independent antigens; moreover, they suppressed normal spleen cell responses to the antigens. The RCS was passed, serially, in young mice and the spleen and ascites cells of these recipients suppressed normal cell responses in vitro. Malignancy resulted in a substantial increase in the proportion of spleen cells of relatively lower density as determined by BSA gradient centrifugation; the cells of lower density were strongly immunosuppressive. The suppressive cells appeared to be neither typical T cells nor macrophages. Humoral suppressive substances associated with the RCS were demonstrated in vivo. The suppressive influence of the RCS may account for the hostile milieu in old BC3F1 mice with respect to lymphohematopoietic cells.