[Toxin-neutralizing monoclonal antibodies to the different domains of anthrax protective antigen]

Anthrax toxin from Bacillus anthracis is a three-component toxin consisting of lethal factor (LF), edema factor (EF), and protective antigen (PA). PA binds to target cells and transports LF or EF into the cell cytosol where they carry out their enzymatic functions. PA can induce protective immunity to the infection of the bacterium and is the major component in the only anthrax vaccine approved by FDA of USA. Mouse hybridoma clones specifically secreting anti-PA monoclonal antibodies (MAbs) were generated by cell fusion technique and their ability to neutralize anthrax lethal toxin activities was screened in vitro on a toxin-sensitive cell line. Nine toxin-neutralizing MAbs obtained were then characterized for the domains of PA they recognize, and the epitope regions they bind were analyzed by competitive binding ELISA. It was found that these MAbs bind four potential neutralizing epitope regions in three different domains of PA. Four MAbs bind to two non-overlapping epitope regions in domain 4 of PA and may prevent the binding of PA to its cell receptor. Four MAbs bind to domain 2, a domain involved in membrane insertion. One MAb binds to domain 3, a region involved in the oligomerization of PA. The results provided supporting evidence that PA has several neutralizing epitopes, and offered potential immunotherapeutic agents for the treatment of anthrax.