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

Abstract

Mycoplasma fermentans incognitus has been isolated from human tissue in patients both with and without AIDS who died of systemic infection. M. fermentans 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 is known about interactions of viable organisms with such cells. Because of the central role of macrophages in chronic inflammation, we examined the effects 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, phagocytosis, rate of cell division, and selected surface markers were evaluated in cultures of THP-1 cells exposed to phorbol myristate acetate (PMA), M. fermentans 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, slightly increasing the percentage of cells positive for FCgammaRI and major histocompatibility complex (MHC) class II antigens. M. fermentans incognitus alone induced an incomplete arrest in the cell cycle at G0 phase, increased phagocytic ability, and enhanced expression of FCgammaRI, CR3, CR4, and MHC class II antigens.

FIG. 1

Mean percentage ± standard deviation (n = 5) of THP-1 cells that ingested latex beads after 24 (A), 48 (B), and 72 (C) h of exposure to PMA and/or M. fermentans incognitus (MFI). The values labeled with an asterisk represent treatments that were significantly different at that time point (P < 0.0001).

FIG. 2

Mean percentage ± standard deviation of cells in different phases of the cell cycle (n = 6) as determined by ethidium bromide staining and fluorescence-activated cell sorter analysis. The data are the averages of two separate experiments. MFI, M. fermentans incognitus.

FIG. 3

Mean percentage ± standard deviation of cells positive for CR3 or CR4 (n = 5) (A) and intensity of expression for positive cells as measured in mean fluorescence units (average ± standard deviation) (B). MFI, M. fermentans incognitus.

FIG. 4

Mean percentage ± standard deviation of cells positive for FcγRI (n = 5) (A) and intensity of expression for positive cells in control and M. fermentans incognitus (MFI)-treated groups as measured in mean fluorescence units (average ± standard deviation) (B). Only one of five samples in the PMA-treated group was positive for FcγRI expression. Intensity of expression was not determined in PMA and MFI-PMA groups because of autofluorescence.

FIG. 5

Mean percentage ± standard deviation of cells positive for MHC class II expression (n = 5) (A) and intensity of expression for positive cells in control and M. fermentans incognitus (MFI)-treated groups as measured in mean fluorescence units (average ± standard deviation). Only two of five samples in the PMA-treated group were positive for MHC class II expression. Intensity of expression was not determined in PMA and MFI-PMA groups because of autofluorescence.