Activation of complement by Naegleria.

Neither Naegleria nor its culture supernatant was found to be directly chemotactic for human neutrophils. Interaction of Naegleria with human serum, however, resulted in the generation of a strong chemotactic stimulus. The reduction of serum activity by heat-inactivation indicated a dependence on serum complement for the interaction. The ability of Naegleria to activate the alternative complement pathway was demonstrated with the use of C2-deficient serum.