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Acne is still a major problem, and treatment options are far from ideal. A number of studies suggest that the species Propionibacterium acnes plays an important role in the pathogenesis, and new data point towards molecular mechanisms by which the organism is able to trigger the host inflammatory response. The current knowledge on P. acnes in relation to acne is reviewed.

Recent data suggest clinical efficacy of specific antigens delivered at mucosal sites in the treatment of certain organ specific autoimmune diseases. This approach appears non-toxic and has no side effects. Phase I/II human trials on multiple sclerosis and rheumatoid arthritis show positive outcomes. Furthermore, animal studies point to beneficial effects on uveitis, diabetes mellitus, transplantation reactions and allergic diseases. The immunological mechanism is oral tolerance, a well known principle for induction of a systemic hyporesponse to specific antigens. The tolerance is most pronounced on delayed type hypersensibility and IgE-mediated reactions. At least three different mechanisms mediate the tolerance. Low doses of antigen induce active suppression, intermediate doses induce clonal T-cell anergy, and high doses induce clonal T-cell deletion. The recent improvements in the understanding of the mechanisms of oral tolerance have fueled an interest in manipulating this principle to develop anti-inflammatory vaccines.