Protective role of immunoglobulin G in immunity to Strongyloides ratti

Serum transfer from hyperimmune rats provided a significant degree of protection against Strongyloides ratti in mature, recipient rats. Eight immune serum pools tested were effective; however, the level of protection, as measured by challenge worm recoveries, ranged from 32 to 91%. Protection did not increase consistently with increasing volumes of immune serum, although as little as 5.0 ml/100 g of body weight afforded consistent protection against challenge infection. The protective effect was exerted against the early migrating tissue stages of the larvae; immune serum given 24 hr after challenge or later had no effect. The specificity of the immune serum's protection was suggested by the removal of this activity by absorption with heat-killed larvae, which have been shown to induce protection by immunization. Fractionation of immune serum showed that a heat-stable 7S component was responsible for protection; no protective activity could be detected in the 19S fraction. Further resolution of the 7S fraction by DEAE ion-exchange chromatography confirmed that the serum's protective activity was in the IgG component. The greatest protection was obtained with the fraction containing predominantly IgG1. In vitro sensitization of infective larvae with rat antibody failed to alter in vivo viability.