Effects of Mycoplasma fermentans incognitus on differentiation of THP-1 cells

Mycoplasma fermentans incognitus has been isolated from human tissue in pat ients both with and without AIDS who died of systemic infection. M. ferment ans incognitus and other strains of M. fermentans have been associated with rheumatoid arthritis. While cell extracts of M. fermentans incognitus can induce changes in murine and human cells of the monocytic lineage, little i s known about interactions of viable organisms with such cells. Because of the central role of macrophages in chronic inflammation, we examined the ef fects of M. fermentans incognitus on surface markers and functions of THP-1 cells, a well-characterized human monocytic cell line. This cell line has been used extensively in studies of macrophage differentiation, especially following exposure to phorbol esters. Changes in cell morphology, phagocyto sis, rate of cell division, and selected surface markers were evaluated in cultures of THP-1 cells exposed to phorbol myristate acetate (PMA), M. ferm entans incognitus, or both. As reported by other investigators, PMA induced THP-1 cells to differentiate into cells resembling tissue macrophages. M. fermentans incognitus only minimally affected changes induced by PMA, sligh tly increasing the percentage of cells positive for FC gamma RI and major h istocompatibility complex (MHC) class II antigens. M. fermentans incognitus alone induced an incomplete arrest in the cell cycle at G(o) phase, increa sed phagocytic ability, and enhanced expression of FC gamma RI, CR3, CR4, a nd MHC class II antigens.