Detection of streptococcal class I M protein in psoriasis by confocal immunofluorescent microscopy.

Epidemiological evidence implicates Streptococcus pyogenes (group A) infection as a common triggering stimulus for psoriasis. Unequivocal demonstration of streptococcal antigens in psoriatic skin has been difficult due to cross-reactive antigens in both normal human tissue and group A streptococci, which complicate immunohistological analysis. In this study cryostat sections of involved psoriatic skin were stained with monoclonal antibody 111-15504 to group A streptococci. The epitope recognized by this antibody was found to be specific for group A streptococci and is associated with class I M protein. Streptococcal antigens were found in the dermal papillae and epidermis of psoriatic skin lesions of 20 out 38 patients. These findings indicate that specific S. pyogenes antigen, associated with class I M protein, is often present in psoriatic lesions. Such an antigen, originating from focal infection elsewhere could be responsible for T-lymphocyte inflammatory responses triggering the development of psoriatic lesions.