Degradation of human IgA by Entamoeba histolytica

To determine whether the virulent enteric pathogen Entamoeba histolytica degrades human IgA molecules, serum and secretory IgA was exposed to viable axenic trophozoites (strain HM1:IMSS), a parasite sonicate, and medium conditioned by incubation with live trophozoites. IgA was completely degraded under all conditions, proteinase activity was maximal at a neutral pH, and there was a four- to eightfold enrichment of amebic IgA proteolytic activity in a soluble fraction of amebic sonicate. Degradation of serum IgA by amebic sonicate was completely inhibited by the cysteine proteinase inhibitors trans-epoxysuccinyl-L-leucyl-amino(4-guanidino)butane (E-64, 100 microM) and benzyloxycarbonyl-phenyl-alanyl-alanyl-fluoromethyl (Z-Phe-Ala-CH2F, 12.5 microM). Secretion of degradative activity, the optimal pH, and the inhibition by E-64 and Z-Phe-Ala-CH2F indicates that cysteine proteinase activity is predominantly responsible for the degradation of human IgA by E. histolytica.