Neutralization of lethal potency and inhibition of enzymatic activity of a phospholipase A2 neurotoxin, crotxin, by non‐precipitating antibodies (Fab)

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Abstract
Rabbit antibodies were prepared against both purified catalytic (component‐B) and purified non‐catalytic (component‐A) subunits of crotoxin, the major phospholipase A2 neurotoxin from the South American rattlesnake. They cross‐react with crotoxin‐like toxins from the venom of several Crotalus species as well as with single‐chain phospholipase A2 neurotoxins from Crotalid and Viperid venoms (agkistrodontoxin and ammodytoxin A) but not from Elapid venoms (notexin). Immunological cross‐reactions of anti‐component‐A and anti‐component‐B sera with crotoxin and with its isolated components A and B showed that component‐A exposes determinants of low immunogenicity which are present on component‐B, whereas the major antigenic determinants of component‐B are not present on component‐A. Anti‐component‐B anti‐bodies, but not anti‐component‐A antibodies, neutralize the lethal potency of crotoxin and inhibit its enzymatic activity. Furthermore, non‐precipitating anti‐component‐B Fab fragments were as potent as antibodies, indicating that crotoxin neutralization results from the binding of the antibodies to the catalytic subunit, rather than the formation of an immuno‐precipitate.

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