Further Observations on the Inhibition of Tumor Growth by Corynebacterium parvum With Cyclophosphamide. IX. Macrophage Content of Tumors in Mice2

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Abstract
Repeated observations with the use of a murine system indicated that tumor growth inhibition resulting from the administration of cyclophosphamide (CY) and Corynebacterium parvum was greater than that occurring after the administration of either agent alone. Investigations were directed toward the determination of whether this effect could be related to an increase in the proportion of macrophages in tumors of treated C3HeB/FeJ female mice. Two different methods for tumor macrophage detection, the Fc receptor analysis and the quantitation of phagocytic mononuclear cells, were employed; the results were compared with two separate controls. No evidence was obtained to indicate that tumor inhibition by any of the treatments employed was associated with an increase in the macrophage content of tumors. Neither local nor systemic administration of C. parvum with or without CY, which resulted in tumor growth inhibition, led to an increase in tumor macrophages. CY given systemically was associated with a rise in the proportion of phagocytic cells, but this rise occurred in tumors lealt affected by such therapy. The content of macrophages in untreated tumors remained constant until tumors reached large sizes, at which time the percentage of Fc receptor-bearing cells decreased. These findings did not imply that the macrophage was uninvolved in the antitumor effect of CY and C. parvum; however, they did suggest that it is unlikely that the effect of local or systemic C. parvum administered with or without CY is mediated by an increase in the number of macrophages within tumors.