The epidermal barrier to Schistosoma mansoni infection.

The stratified epithelium serves as protection for underlying tissues and organs, and the structural fitness of the epidermal cells has been extensively reported. We studied the possible roles played by the epidermis as a barrier against the migration of Schistosoma mansoni larvae. Freshly shed cercariae were collected and placed on the back skin of 2-day-old rats. Electron microscopy of biopsies taken at various intervals showed the larvae and their secretory granules in keratinocytes in which the cytoplasm had become homogeneous in appearance. SDS gel electrophoresis showed the digestion of purified epidermal keratin (60K protein) by a proteinase secreted from cercariae, but this activity was inhibited by an inhibitor purified from epidermal cells. These findings suggest that epidermal cells function both structurally and chemically as a barrier against cercariae invasion.