Alternative pathway activation of complement in fetal lamb serum by Trichostrongylus vitrinus larvae.

Fetal lamb serum (FLS) complement activated by incubation with Trichostrongylus vitrinus larvae was deposited on the larval surface and its presence was demonstrated by leucocyte and erythrocyte adherence reactions and by analysis of antisera from guinea-pig immunized with the larvae. The complement activation proceeded in the apparent absence of antibody and in the presence of ethylene glycol tetracetic acid (EGTA) or Mg++-EGTA but not ethylenediamine tetracetic acid (EDTA). FLS heated to 50 degrees C for 30 min was inactive, but activity was restored by addition of FLS factor B alone or factor B plus Mg++-EGTA. FLS treated with zymosan or inulin was inactive. These results suggest that this non-immune activation of sheep complement by T. vitrinus takes place via the alternative pathway.