Skin basement membrane zone: a depository for circulating microbial antigen evoking psoriasis and autoimmunity.

Background: Elevated levels of antibody to streptococcal exoenzymes have been found in patients with psoriasis or psoriatic arthritis. Research on the role of streptococcal antigen in psoriasis has been hampered by a potential molecular mimicry between streptococcal epitopes and human epidermal keratin.

Objective And Methods: Evidence of microbial product was sought in skin biopsies of psoriasis patients thought clinically to have either streptococcal carrier state or gastrointestinal candidal colonization. A polyclonal antibody to streptococcal-derived exoenzymes unlikely to share antigenic structures with normal human skin, and an anticandidal antibody, were used with linked streptavidin biotin amplification stain.

Results: The predicted microbial product appeared heavily in lesional epidermis, but unexpectedly also as a thin deposit along the skin basement membrane zone (SBMZ) of apparently unaffected skin. Staining was negative for nonpsoriatic subjects.

Conclusions: The findings support a direct effect of microbial antigen in psoriasis. They also suggest an important role for SBMZ as a very large adhesive surface in the first step of a process of percutaneous epidermal elimination of foreign antigens and microbial toxins. The many autoimmune phenomena seen so often at the SBMZ are probably a physiologic part of this important immune function. Efforts to enhance the adhesive properties of SBMZ should be exploitable for both diagnostic and therapeutic benefit.