Immunological studies on aphthous ulcer and erythema nodosum-like eruptions in Behcet's disease.

Patients with Behcet's disease show an intense delayed hypersensitivity (DH) reaction to a group of streptococcal bacteria. We have attempted to detect deposits of immune complexes and to analyse cytological reactions in the aphthous ulcers and erythema nodosum (EN)-like eruptions. Deposits of IgM and positive fluorescence of anti-streptococcal group D serum were found in vessel walls and sites infiltrated by inflammatory cells. Cytological analysis has revealed that the inflammatory infiltrating cells are mainly composed of activated T-cells and macrophages in association with natural killer cells. These results suggest that DH reactions with antigen-antibody mediated cytotoxicity may play an important role in causing the lesions of Behcet's disease.