Immunity and immunopathology following reinfection of mice cured of chronic schistosomiasis mansoni.

The effect of curative treatment of murine schistosomiasis mansoni on resistance to reinfection and on granulomatous hypersensitivity following reinfection was studied. The sera of mice with light chronic Schistosoma mansoni infection of 32 weeks duration were tested by immunodiffusion analysis with soluble egg antigens for a precipitin band containing an antigen specific for eggs in order to identify bisexual infections. A group of the 32 week bisexually-infected mice were treated with niridazole, as was a similar group of uninfected mice. Six weeks later (at 38 weeks) the previously infected mice were injected subcutaneously with 30 cercariae and the uninfected mice with 20 cercariae. On perfusion 12 weeks later the secondarily infected mice had a percentage worm yield following infection of 16 while that in the primarily infected mice was 60. Twelve weeks after reinfection (at 50 weeks), the previously infected mice had moderate hepatosplenic disease similar to the mice which had remained constantly infected for 50 weeks, and formed relatively small granulomas around eggs injected into their pulmonary microvasculature. In spite of much lower liver egg counts, particularly severe hepatosplenic disease was seen in the previously uninfected mice. When eggs were injected into their lungs, however, very large granulomas were observed. These experiments suggest that both immunity and modulation of immunopathology are residual after curative treatment.