Epithelial polymeric immunoglobulin receptors.

The secretory immune system, which leads to secretion of polymeric immunoglobulins along mucosal surfaces, has not been shown to have any definite role in cutaneous immunology, although the polymeric immunoglobulin receptor, secretory component (SC), has been found in sweat glands and possibly in the epidermis. The purpose of this study is to examine normal human skin and cultured human keratinocytes for the presence of SC. Positive staining for SC was found in sections of normal human skin along the basement membrane zone with use of a polyclonal antibody to SC and focally on the surfaces of epidermal cells with use of a monoclonal antibody to SC. Granular cell-surface fluorescence of an intensity far less than that of the positive control HT 29 cells was seen when cultured human keratinocytes were stained for SC by indirect immunofluorescence (IF). Study of lysates of both HT 29 cells and HK by immunoblotting have been negative, perhaps due to destruction of the protein or loss of antigenicity during the extraction process. If human keratinocytes are capable of expression of SC, and the receptor can interact with IgA and IgM, this might be a mechanism for protection of the skin from microbial agent or foreign antigens and might be relevant to the deposition of IgA seen in certain skin diseases.