Methylcholanthrene-induced tumors in adult and in aging rats: infiltrating cells and their ADCC activity.

In our previous studies we found that the slower growth of syngeneic, immunogenic MC-induced sarcoma (MC-Sa) in aging rats was followed by the higher activity of spleen lymphocytes in ADCC assay. The purpose of the present paper was to study infiltrating cells of immunogenic and non-immunogenic MC-Sa and to estimate in situ ADCC activity in relation to the growth of MC-Sa transplants in adult and aging rats. It was found that MC-Sa's were infiltrated mainly by lymphocytes. Among cells infiltrating tumor the high percentage of cells with Fc receptor was present. During progressive tumor growth the percentage of infiltrating cells and also FcR+ cells significantly decreased within immunogenic MC-Sa, but did not change in the case of the non-immunogenic MC-Sa. In cell infiltrates of both tumors no differences between adult and aging rats were observed. At early stages of the tumor growth the cells active in ADCC assay were present within both MC-Sa. The slower growth of immunogenic MC-Sa in aging rats compared with adults was connected with longer maintenance of ADCC activity in situ. In the case of non-immunogenic MC-Sa, which grew at similar rate in both groups of rats, no differences in ADCC activity between adult and aging animals were observed. It is suggested that in situ ADCC activity may be one of the mechanisms responsible for the slower growth of immunogenic MC-Sa in aging rats.