Immunohistologic evidence for the role of antibody and macrophages in regression of the murine T1699 mammary adenocarcinoma

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Abstract
The regression or progression of the T1699 murine mammary adenocarcinoma was analyzed with histologic and immunohistologic techniques to determine the tissue distribution of both macrophages and antitumor antibody. Changes in integrity of tumor blood vessels were apparent during tumor growth and regression. Tumors at early stages of growth were invaded in the capsule by multiple vascular branches which later permeated the tumor. Following the appearance of anti‐tumor antibody in the serum, these vessels often showed immune complex deposition which preceded vessel leakage, destruction and hemorrhage. After these changes, tumor cells appeared coated with antibody. Macrophages appeared predominantly in the tumor capsule during early stages of tumor growth, while at later stages they were observed within tumors most prominently near the edge of growing hemorrhagic and necrotic areas. As tumors regressed, connective tissue septation lined by macrophages became apparent. Phagocytosis of seemingly intact tumor cells was common and appeared to account for much of the loss in tumor cell numbers. In immunosuppressed animals (ATXBM, 450R) in which tumor progression always occurred, the above features were markedly diminished or absent. This model emphasizes the interplay of many factors in tumor regression. These include immune complex deposition, blood vessel destruction, macrophage infiltration and connective tissue development, all of which are associated with tumor regression and seem to be infrequent and/or inconsequential during progressive tumor growth.