A monoclonal antibody directed against the non-toxic subunit of a dimeric phospholipase A2 neurotoxin, crotoxin, neutralizes its toxicity

Crotoxin is the main toxic component of the venom of the South-American rattlesnake Crotalus durissus terrificus. It is a phospholipase Ap neurotoxin constituted by the association of two subunits: an acidic, non-toxic and non-enzymatic subunit (CA) and a basic, weakly toxic phospholipase Ap (CB). A murine monoclonal antibody directed to the non-toxic subunit CA, A-56.36, was shown to fully neutralize the toxicity of crotoxin. When the in vitro pharmacological properties of crotoxin were further tested, A-56.36 was shown to enhance the enzymatic activity on negatively-charged phospholipids and to increase the acetylcholine release triggered by crotoxin on Torpedo synaptosomes. These effects were explained by the fast dissociation of the crotoxin complex in the presence of the monoclonal antibody A-56.36 and the immunocomplexation of CA, with CB being released in solution. CB is less toxic than crotoxin, has a higher enzymatic activity and triggers a higher acetylcholine release than crotoxin, due to its strong enzymatic activity. A single-chain variable fragment antibody was prepared from monoclonal antibody A-56.36. It binds to CA with a similar affinity than the parental immunoglobulin and exhibits similar effects on the in vitro pharmacological properties of crotoxin.