Only recently have human sweat glands been demonstrated to secrete immunoglobulins (Ig), paralleling Ig secretion in mucosal epithelia. It is well established that Ig protect mucosal membranes against infections by binding to surface structures of microorganisms. In view of these findings immunohistochemical studies were performed to determine if microbes on the skin surface are coated by Ig as proposed for mucosal bacteria and fungi.

Smear preparations from the skin and oral cavity rich in micro-organisms were subjected to immunoperoxidase staining using anti-secretory component (SC), -IgA, -IgM, -IgG antibodies. An immunogold labeling technique of microbial suspensions of sweat and saliva was adapted to correlate the results on an ultrastructural level. Negative controls included unsuccessful staining for IgA in preparations obtained from an IgA-deficient patient as well as nonreactivity of subcultured microorganisms for all Ig classes or SC. Smear preparations from both the oral cavity and skin surface exhibited labeling of bacterial or fungal elements with anti-IgA, -IgM, -IgG, and -SC antibodies. Skin bacteria revealed a lower number of reactive microbes as compared to saliva. Staining intensity for the different Ig classes exhibited intra- and interindividual variations. Immunoelectronmicroscopically, Ig and SC could be detected either directly along the cell wall of coccal, coryneform, and fungal elements or on floccular and fimbrial material adhering to the bacterial surface.

It is concluded that secretory Ig of the skin cover surface structures of microorganisms and thus modify their adhesional and/or infectious properties, resembling humoral surface immunity on mucous membranes.