Membrane attack complex of complement in dermatitis herpetiformis.

The assembly of membrane attack complex (MAC) of complement implies activation of complement to the attachment of C9 and the presence of MAC on tissue suggests a possible pathogenic role for complement in disease since MAC is able to damage membranes. We examined normal skin of five patients with dermatitis herpetiformis for the presence of MAC using a monoclonal antibody (poly C9-MA) that recognizes a neoantigen of C9 that is not present on monomeric C9 but is common to both isolated MAC and to polymerized C9. Granular deposits of polymerized C9 were found at the sites of IgA deposition in the dermal papillae of normal skin from all patients. The pathologic importance of this finding is uncertain.