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-leucylamino(4-guanidino)butane (E-64, 100 muM) and benzyloxycarbonyl-phenyl-alanyl-alanyl-fluoromethyl ketone (Z-Phe-Ala-CH2F, 12.5 muM). Secretion of degradative activity, the optimal pH, and the inhibition by E-64 and Z-Phe-Ala-CH2F indicates that cysteine proteinase activity is predominately responsible for the degradation of human IgA by E. histolytica.