FACS analysis of tumor-associated macrophage replication: differences between metastatic and nonmetastatic murine mammary tumors.

The proliferation activity of adherent, tumor-associated macrophages (TAM) from three related murine mammary carcinoma lines was measured by fluorescence-activated cell sorter (FACS) analysis of the incorporation of 5'-Bromo-2'deoxyuridine (BrdU) in vivo during a 1 hr period prior to tumor removal. The tumor lines examined were line 67 which is nonmetastatic following either subcutaneous (SC) or intravenous (IV) injection, line 168 which colonizes the lung after IV injection but not SC, and line 66 which can colonize the lung from either site. The percentage of total cells identified morphologically as macrophages were similar for tumors from lines 66 and 67 (41% and 38%, respectively), as compared to line 168 tumors, in which, after digestion, 27% of cells were identified as macrophages (P less than or equal to 0.05). Adherent TAM from line 66 tumors had the greatest percentage of BrdU incorporating cells, with an average of 22%. This was statistically significant (P less than or equal to 0.01) from TAM from tumors of line 67, which were 13% positive. The percentage of adherent TAM from line 168 tumors (18% positive) was also significantly different from 67 TAM (P less than or equal to 0.01). These results demonstrate a possible correlation between the percentage of TAM undergoing replication and the ability of the host tumor to colonize the lung. There is no apparent relationship between the percentage of TAM in replication and the number of macrophages associated with a tumor.