A solid-phase sandwich radioimmunoassay for Entamoeba histolytica proteins and the detection of circulating antigens in amoebiasis.

A sensitive and specific immunochemical assay for Entamoeba histolytica antigens would be a valuable tool for clinical diagnosis, to study the sequelae of amoebiasis, and to screen for the expression of amoebic proteins in recombinant bacterial clones. The major impediment toward developing such an assay is the cross-reactivity of anti-E. histolytica antisera with a wide range of mammalian serum proteins. A rabbit anti-E. histolytica antiserum was repeatedly passed over three bovine serum protein immunoadsorbents and affinity purified over an E. histolytica protein-Sepharose 4B matrix. The purified antibody was radiolabeled and formed the upper layer of two specific and sensitive sandwich radioimmunoassays for amoebic proteins. One assay used a rabbit antiamoebic antibody solid phase and the other a human antibody solid phase. The latter assay proved capable of detecting amoebic antigens in the polyethylene glycol precipitates of sera from 21 of 21 patients with amoebiasis (and none of 22 control subjects).