We have recently identified a 150-kDa
surface antigen of Entamoeba histolytica as an intermediate subunit (Igl) of
galactose- and
N-acetyl-D-galactosamine-inhibitable
lectin, which is a
cysteine-rich
protein consisting of 1,101
amino acids (aa) and containing multiple CXXC motifs in amino acid sequences. In the present study, full-length Igl except for the
signal sequences (aa 14 to 1088) and three fragments of Igl-the N-terminal part (aa 14 to 382), the middle part (aa 294 to 753), and the C-terminal part (aa 603 to 1088)-were prepared in Escherichia coli, and the reactivity of these
recombinant proteins with sera from patients with
amebiasis was examined by means of
enzyme-linked
immunosorbent assay (ELISA). Sera from 57 symptomatic patients with
amebic liver abscess or
amebic colitis, sera from 15 asymptomatic
cyst passers, sera from 40 individuals with other
protozoan infections, and sera from 50 healthy controls were used. The sensitivity and specificity of the recombinant full-length Igl in the ELISA were 90 and 94%, respectively. When three fragments were used as
antigens in the ELISA, the sensitivities were 56% in the N terminus, 92% in the middle part, and 97% in the C terminus. The specificities of the three
antigens were 96% in the N terminus and 99% in both the middle and C-terminal fragments. These results demonstrate that Igl is well recognized in not only symptomatic but also asymptomatic patients with E. histolytica
infection and that the carboxyl terminus of Igl is an especially useful
antigen for the serodiagnosis of
amebiasis.