Schistosoma mansoni: development of primary infections in mice genetically deficient or intact in the fifth component of complement.

The influence of the late components of complement (C) on the percutaneous primary infections with Schistosoma mansoni was studied in inbred mice genetically deficient or intact in C5. Worm recoveries were diminished in C5-deficient male mice as compared to C5-intact animals. Twenty-four-day-old parasites were also shorter following growth in C5-deficient animals. At 7 weeks after infection, female schistosomes, but not male parasites, were shorter and fewer eggs/schistosome pair were deposited in the livers of C5-deficient as compared to C5-intact male mice. In addition to the presence of C5, the mouse sex was found to influence the outcome of an infection. Schistosomes showed a reduced infection rate and were relatively stunted after 24 days of growth in female mice in the two strains as compared to male mice of the corresponding strains. The results suggest that C5 plays no role in defence against a primary infection in mice.