Macrophage-like synoviocytes originate in the bone marrow, like other mononuclear phagocytes, and are constantly replaced via the circulation. In rheumatoid synovium sections, 80-100% of the synovial lining cells are macrophage-like cells functioning as antigen processing- and antigen-presenting cells to T lymphocytes. Monocyte and lymphocyte traffic into the rheumatoid arthritis (RA) synovium is mediated by adhesion molecules such as endothelial-leukocyte adhesion molecule-1 (ELAM-1), vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecules-1 and -2 (ICAM-1 and ICAM-2), as well as monocyte chemotactic protein 1 (MCP-1) and beta 2 integrins (CD11 a,b,c/CD18). Macrophage-like cells in the RA synovium are highly activated based on their morphology, surface class II HLA antigen expression, and synthesis of cytokines such as interleukin-1 beta (IL-1 beta), tumor necrosis factor alpha (TNF-alpha), interleukin-6 (IL-6), granulocyte-macrophage colony-stimulating factor (GM-CSF), macrophage CSF, and transforming growth-factor beta (TGF-beta). Evidence for type 1 (higher affinity) and type 2 (lower affinity) androgen (ARs) and estrogen receptors (ERs) on macrophage-like synoviocytes in either male or female synovial samples from both RA patients and controls has been reported. In particular, ERs have also been found on CD8+CD29+ CD45R0+ T lymphocytes (memory), infiltrating rheumatoid synovial tissues. Sex hormones have been found to influence macrophage activity in experimental and clinical conditions such as RA. Generally estrogens have immunostimulatory effects, whereas androgens are immuno-suppressive.(ABSTRACT TRUNCATED AT 250 WORDS)