Immunopathology of Dermal Reactions Induced by Schistosoma Mansoni Cercariae and Cercarial Extract *

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Abstract Mice infected with Schistosoma mansoni and normal mice were exposed to viable S. mansoni cercariae, and the exposed areas were biopsied at ½, 1, 2, 4, 8, 16, 24, 36, 48, and 120 hours. The initial histologic response (2–8 hours after challenge) of previously infected animals was characterized by edema and a progressive, predominantly polymorphonuclear infiltrate. By 16 and 24 hours, the schistosomules were the foci of intense mixed cell infiltrates, and by 36 and 48 hours, dense mononuclear infiltrates were evident. Normal mice showed only edema and slight polymorphonuclear infiltrates, and by 16 hours most of the schistosomules had migrated through the dermis. Intradermal challenge of infected and uninfected mice with a crude saline cercarial extract produced reactions similar to those described for the two groups after cercarial penetration. Normal mice were also challenged by cercarial exposure or injection of cercarial extract after passive transfer of either lymphoid cells or serum from infected or normal mice. Sera from infected mice passively immunized normal mice, which then responded with an early (5-hour) polymorphonuclear infiltrate against cercariae. Lymphoid cells from infected mice passively immunized normal mice which then developed a late (30-hour) mononuclear infiltrate against either schistosomules or cercarial extract. It is concluded that mice develop both humoral and cell-mediated immune responses against the cercarial stage of S. mansoni.