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

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Abstract
Fetal lamb serum (FLS) complement activated by incubation with T. vitrinus larvae was deposited on the larval surface and its presence was demonstrated by leukocyte 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 tetraacetic acid (EGTA) or Mg2+-EGTA but not EDTA. FLS heated to 50.degree. C for 30 min was inactive but activity was restored by addition of FLS factor B alone or factor B plus Mg2+-EGTA. FLS treated with zymosan or inulin was inactive. This non-immune activation of sheep complement by T. vitrinus apparently takes place via the alternative pathway.