A MONOCLONAL-ANTIBODY DIRECTED AGAINST THE NONTOXIC SUBUNIT OF A DIMERIC PHOSPHOLIPASE A(2) NEUROTOXIN, CROTOXIN, NEUTRALIZES ITS TOXICITY

Crotoxin is the main toxic component of the venom of the South-America n rattlesnake Crotalus durissus terrificus. It is a phospholipase Ap n eurotoxin constituted by the association of two subunits: an acidic, n on-toxic and non-enzymatic subunit (CA) and a basic, weakly toxic phos pholipase Ap (CB). A murine monoclonal antibody directed to the non-to xic subunit CA, A-56.36, was shown to fully neutralize the toxicity of crotoxin. When the in vitro pharmacological properties of crotoxin we re 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 immunocomplexatio n of CA, with CB being released in solution. CB is less toxic than cro toxin, has a higher enzymatic activity and triggers a higher acetylcho line release than crotoxin, due to its strong enzymatic activity. A si ngle-chain variable fragment antibody was prepared from monoclonal ant ibody A-56.36. It binds to CA with a similar affinity than the parenta l immunoglobulin and exhibits similar effects on the in vitro pharmaco logical properties of crotoxin.