Increase in the proportion of cells with the C'3 receptor in BALB/c mice bearing mammary tumors.

Transplantation of mammary tumors originally induced by dimethylbenzanthracene caused splenomegaly and an increase in the total population of spleen cells paralleling the increase in tumor size. At least part of the hypercellularity was due to in situ proliferation as evidenced by the increased number of blast forms and mitotic figures. The cells were characterized with respect to parameters generally associated with B-cells; surface immunoglobulins as detected by immunofluorescence and C'3 receptors as determined by rosette formation with sheep red blood cells (SRBC) coated with rabbit anti-SRBC and mouse complement. There was no change in the percentage of B-cells with surface immunoglobulin in tumor-bearing mice compared with the control animals. However, there was a profound change in the representation of cells bearing C'3 receptors. The percentage of the cells increased dramatically with tumor growth. Various possibilities regarding the nature and function of these cells are considered.