Detection of Entamoeba histolytica immunoglobulins G and M to plasma membrane antigen by enzyme-linked immunosorbent assay.

Sixty-one serum specimens from 22 patients with clinically diagnosed amoebic liver abscess (ALA), 10 hospitalized patients with a variety of diseases other than amoebiasis, 12 normal healthy controls, and 17 subjects from an amoebiasis-endemic area were assayed by enzyme-linked immunosorbent assay (ELISA). The plasma membrane fraction of axenic cultures of Entamoeba histolytica HK9 separated from other subcellular fractions by differential centrifugation was used as the antigen to detect specific immunoglobulin G (IgG) and IgM antibodies. Using a single serum dilution of 1/100 and optical densities at 492 nm of 0.200 and 0.250 as the cutoff values for the IgM and IgG ELISAs, their respective sensitivities in 22 ALA patients were 91% (20 of 22) and 95% (21 of 22). In 22 patients (10 hospitalized and 12 normal healthy controls), the specificities of the IgM and IgG ELISAs were 95% (21 of 22) and 91% (20 of 22), respectively. All five asymptomatic carriers of pathogenic E. histolytica were seropositive by the IgG ELISA and the amoebic gel diffusion test (AGDT). The AGDT was positive for three of six culture-negative controls, while the IgG ELISA was positive for all six. For six asymptomatic carriers of nonpathogenic zymodemes, the AGDT was positive for two, and the IgG ELISA was positive for three. There was an excellent correlation (r = 0.96) between the IgG ELISA and the AGDT. Only one of six culture-negative controls, none of the asymptomatic carriers of pathogenic E. histolytica, and one of six carriers of nonpathogenic E. histolytica were seropositive by the IgM ELISA, thus highlighting the specificity of the IgM ELISA in the diagnosis of ALA. It is believed that the use of plasma membrane fractions has improved the diagnostic potential of the IgM ELISA.