Immunoglobulin G-dependent classical complement pathway activation in neutrophil-mediated cytotoxicity to infective larvae of Angiostrongylus cantonensis

The participants of antibody and complement in cell-mediated adherence and cytotoxicity to infected larvae (L3) of Angiostrongylus contonensis was investigated in vitro. Of the different cell types involved in the reaction, neutrophils were seen to have a predominant role in immune serum-dependent adherence and cytotoxicity to L3. In the presence of immune serum, cytotoxicity to L3 by neutrophils from infected rats was twice that of neutrophils from normal rats. Although mononuclear cells and eosinophils from infected rats significantly increased the adherence to L3, they had little tethal effect on L3. A further study using gel filtration (Sephacryl S-200) and affinity chromatography (protein A) revealed that immunoglobulin G (IgG) alone was responsible for the complement activation in neutrophil-mediated killing of L3. Neither adherence nor cytotoxicity to L3 by neutrophils were affected when immune serum was heated to 50°C or treated with zymosan, but they were markedly decreased when immune serum was treated with Mg²⁺-ethylene glycol-bis-(̄-aminoethyl ether)-N,N.N',N'-tetraacetic acid. The results of this study indicate that the neutrophil-mediated adherence and cytotoxicity to L3 of A. cantonesis are mediated through IgG-dependent classical complement pathway activation.