Immunological aspects of infections with Schistosoma mansoni.

Abstract

Summary 1. Antibody studies in the sera from human subjects infected with Schistosoma mansoni have revealed the presence of cercarial precipitins, cercarial agglutinins, and circumoval precipitins. Adult precipitins were also detected, but in low titers and in a small per cent of the sera tested. 2. There were differences observed in the concentration of these antibodies as related to the duration of infection. In early infections (40 to 240 days after exposure to cercariae) cercarial precipitins and agglutinins have high titers but become low or negative in infections of long duration (10 years and over). Circumoval precipitins are present in both recent and old infections but become more active in older infections. 3. The adult, cercarial, and egg antibodies as produced by artificial immunization of the rabbit are stage specific. Treatment of rabbit anti-serum with lyophilized adult or cercarial material results in the absorption of the homologous but not of the heterologous antibodies. Treatment of anti-adult, anti-cercarial, and anti-egg sera with egg material absorbs only the homologous and the cercarial antibodies. This postulates a cercarial factor in the egg. 4. No circumoval precipitins were detected in the sera from mice with single sex infections. This provides further evidence confirming stage specificity of the circumoval antibody which only develops in the presence of eggs. 5. Successful Fuadin therapy as determined by repeated negative stools and rectal biopsy reduces the circumoval activity of sera. This effect was observed within a year after therapy. The reduction in circumoval precipitin content of serum may be used as a test to determine the therapeutic effect of Fuadin or other anti-schistosome drugs. The circumoval precipitin test, therefore, is both of diagnostic and prognostic value. 6. Intradermal response to egg antigen differs from that elicited against adult and cercarial antigens in that a negative reaction is observed in active cases. The skin response becomes positive after treatment of infection. 7. Knowledge of stage-specific antibodies, and the time during the course of infection when their concentrations are highest, is of great importance in the serological diagnosis of schistosomiasis. Stage-specific antibodies are also of great interest in the study of the mechanism of acquired immunity to schistosomiasis.