An hypothesis to link the opposing immunological effects induced by the bacterial lysate OM-89 in urinary tract infection and rheumatoid arthritis.

Extracts of lysed pathogenic bacteria were developed approximately 4 decades ago as oral vaccines in order to stimulate efficient specific immune and proinflammatory responses in patients experiencing recurrent infections, the ultimate aim being to rid the patient of the pathogen responsible for the infections. OM-89, a lysate of Escherichia coli, is clinically effective in patients who experience recurrent urinary tract infections by activating both innate and adaptive immunity. If immune activation is necessary to combat infectious pathogens, it may appear at first sight to be detrimental in patients with autoimmune diseases. However, OM-89 has also shown clear efficacy in patients with rheumatoid arthritis or with undifferentiated spondyloarthropathies, probably through oral tolerance and the long-term activation of regulatory cells. These phenomena may be explained by a hypothesis that immune exclusion and oral tolerance, both key functions of the gut, may be boosted by adjuvant-like molecules within orally administered OM-89.