Macrophage-secreted TNFα enhances breast fibroblast proliferation. Primary human monocytes/macrophages were isolated, differentiated, treated with estrogen (10-10 M) for 24 hr and conditioned media (CM) were collected. Primary human breast fibroblasts were placed in 2% charcoal-stripped serum-containing media 24 hr prior to treatment with 2% charcoal-stripped serum-containing media + estrogen (10-10 M), media + 10 ng/ml TNFα (T), + TNFα inhibitor (I), the combination TNFα + inhibitor (T+I), macrophage-conditioned media (CM) or CM + TNFα inhibitor (CM+I). For each assay, cells were treated for three days then trypsinized and counted. Data shown are from one representative experiment of two independent experiments. *P < 0.05 from CM.