Immunochemical cross-reactivity of neurotoxic phospholipase A2 enzymes from Indian cobra (Naja naja naja) venom using polyclonal antibodies

Abstract

Rabbit antibodies were prepared against purified phospholipase A2 (NN-XIa-PLA2) from Indian cobra (Naja naja naja) venom. The PLA2 has haemolytic, neurotoxic, myotoxic, cytotoxic and oedema-inducing activities apart from the catalytic activity. The immunological cross-reactivity of structurally similar neurotoxic PLA2s was investigated using enzyme-linked immunosorbent assay (ELISA) and immunodiffusion. Anti-NN-XIa-PLA2 IgG cross-reacted with other purified neurotoxic PLA2s from the same venom. Immunochemical cross-reactions of anti-NN-XIa-PLA2 IgG with NN-XIa-PLA2, NN-XIb-PLA2, NN-XIII-PLA2, NN-IVb1-PLA2 and NN-Vb-PLA2 were shown by a very high ELISA titre and a single precipitin band on double immunodiffusion agarose plates. The catalytic activity of these PLA2s was inhibited dose-dependently by anti-NN-XIa-PLA2 IgG but was unable to neutralize lethality and neurotoxic symptoms in experimental animals injected with neurotoxic PLA2. Anti-NN-XIa-PLA2 IgG fails to neutralize myotoxicity and oedema-inducing activities of NN-XIa-PLA2 and NN-XIII-PLA2. Anti-NN-XIa-PLA2 IgG inhibited cytotoxic effects of NN-XIa-PLA2 dose-dependently, but failed to inhibit NN-XIII-PLA2-induced cytotoxicity. Direct haemolytic activity of NN-XIa-PLA2 and NN-XIII-PLA2 was inhibited dose-dependently by these antibodies. The results indicate the presence of separate catalytic and pharmacologic site(s).