Effect in vitro of a bacterial extract (OM-89) on interleukin 1 and interleukin 2 production by peripheral blood mononuclear cells from healthy subjects and rheumatoid arthritis patients.

The effect of a lyophilized extract from Escherichia coli strains (OM-89) on interleukin 1 and interleukin 2 production was studied by using peripheral blood mononuclear cells (PBMC) from healthy volunteers and from patients suffering from rheumatoid arthritis (RA) since, in this autoimmune disease, an abnormal cytokine network has been already described. The secretion of interleukin 1 (IL-1) was investigated in supernatants of monocytes purified by adherence, and measured by the C3H/HeJ thymocyte co-mitogenic assay. OM-89 was able to induce the secretion of IL-1 by normal and RA monocytes to about half of the level reached when the same cells were stimulated by lipopolysaccharide. The production of interleukin 2 (IL-2) was investigated in supernatants of PBMC, stimulated or not by phytohaemagglutinin (PHA) and mixed or not with various concentrations of OM-89. The level of IL-2 in supernatants, as measured by the stimulation of the CTLL2 murine cell line, was lower in RA supernatants than in control ones. In the presence of PHA and OM-89, the IL-2 production was enhanced and normalized in supernatants from RA patients. Such data may help to explain the clinical improvement previously reported in RA patients orally treated with OM-89.