THE NEUTRAL CYSTEINE PROTEINASE OF ENTAMOEBA-HISTOLYTICA DEGRADES IGGAND PREVENTS ITS BINDING

Patients infected with Entamoeba histolytica generate specific IgG tha t does not prevent invasive amebiasis or recurrent infection, Studies investigated whether the effectiveness of the human humoral response w as limited by cleavage of IgG by the extracellular neutral cysteine pr oteinase of E. histolytica trophozoites, one of the first amebic produ cts to interact directly with components of host defenses, Purified pr oteinase cleaved polyclonal human and monoclonal murine IgG in a dose- dependent manner, Peptide sequencing of the major cleavage fragment(s) , which contained the protein A binding site, suggested that cleavage occurred near the hinge region, Intact trophozoites also cleave IgG in both growth media and serum-free media, Cleared monoclonal antibody t o a 29-kDa surface antigen of E. histolytica bound to trophozoites 83. 5% +/- 6.7% less than did uncleaved antibody, These results suggest th at cleavage of IgG by the extracellular cysteine proteinase may limit the effectiveness of the host humoral response.