Lack of correlation between in vitro and in vivo activation of complement in mice by infective Trichinella spiralis larvae

Very little is known about the role played by complement in vivo during Trichinella spiralis infections, although previous reports indicate that it binds readily to the surfaces of muscle stages of the parasite in vitro. In order to study the binding of complement to muscle-stage larvae in vivo, larvae were recovered from BALB-c inbred, NFR/N inbred, and Swiss white outbred mice from 20 to 95 days postinfection. The presence of C3 was examined by direct immunofluorescence and leucocyte- and erythrocyte-adherence tests. Complement was found on a few larvae from the outbred strain and only rarely on larvae from the 2 inbred strains. Histological sections prepared from inbred strains and used in immunofluorescence tests to study in situ complement activation and binding were negative. Larvae from all 3 mouse strains bound complement 100% of the time when it was added to the worms in vitro. The results indicate that extrapolation from in vitro to in vivo activation and binding of complement to T. spiralis larvae may not be valid.