Effect of a bacterial extract on cellular and humoral immune responses in humans.

A lyophilized extract from E. coli (OM-89) was studied for its immunomodulating properties and tolerance in humans. Its oral administration to healthy volunteers produced a selective increase in the active T-cell population without changes in other lymphocyte populations. A significant increase in the proliferative response to concanavalin A and phytohemagglutin was recorded, but not to pokeweed mitogen. No significant changes were observed in the serum levels of IgG, IgA and IgM. The clinical and biological tolerance of OM-89 was excellent, without any adverse side-effects or production of circulating immune complexes or of autoantibodies, while the in vitro investigation showed that it is not a mitogen. Thus in healthy subjects OM-89 seems to act mainly on the cell-mediated immune responses.