Immune response is greater in females than in males and lymphocytes/monocytes from female subjects (or tested in vitro with estrogens) show higher immune/inflammatory reactivity. In order to test in vitro the interactions between 17beta-estradiol (E2--10(-9) M), testosterone (T--10(-8) M) and the antiproliferative/immune suppressive drug Leflunomide metabolite A77 1726 (LEF-M--30 microM) employed in rheumatoid arthritis (RA), their combined effects were evaluated on inflammatory cytokine (CK) expression/production in cultures of differentiated macrophages (M) (from activated THP-1 monocytes) and primary cultures of RA synovial macrophages (SM). TNFalpha, IL-6 and TGFbeta were detected by immunocytochemistry (ICC), Western blot analysis (WB) and reverse transcriptase-polymerase chain reaction (RT-PCR). The ICC, WB and RT-PCR showed a significant down-regulation induced by LEF-M on CK expression by cultured M when compared to untreated cells (IL-6 p < 0.01, TNFalpha p < 0.001, TGFbeta p < 0.01). At ICC analysis E2 increased CK expression, whereas T decreased the expression, confirmed by WB and RT-PCR (range between p < 0.05 and p < 0.001). LEF-M treatment significantly downregulated the CK expression in E2/T treated M: the effect was more significant in LEF-M plus T-treated cells versus controls (range between p < 0.01 and p < 0.001). Concerning the RA SM, the results were replicated (range between p < 0.05 and p < 0.001). E2 seems to contrast, but T seems to synergize the LEF-M activity. Results might support a stronger therapeutical efficacy, at least for LEF, in male RA patients, as already reported by clinical evidences.