Secretory immunoglobulin A antibodies to the galactose-inhibitable adherence protein in the saliva of patients with amebic liver disease.

Monoclonal antibodies directed against the 260-kD galactose-inhibitable adherence protein (GIAP) of Entamoeba histolytica inhibit binding of amebic trophozoites to purified colonic mucins, suggesting that anti-GIAP secretory immunoglobulin A (sIgA) may have a role in host defense in invasive amebiasis. We determined by enzyme-linked immunosorbent assay (ELISA) whether a salivary anti-GIAP sIgA response was present in patients from the Republic of South Africa with invasive E. histolytica infection. In 13 patients with amebic liver abscess (ALA), salivary anti-GIAP sIgA was significantly higher (mean +/- SD optical density [OD] = 0.448 +/- 0.258) than that determined for seven South African adult patients hospitalized with nonamebic illness (0.084 +/- 0.072; P = 0.002), seven healthy South African Adults (0.194 +/- 0.119: P = 0.025), and seven healthy adults from Charlottesville, Virginia (0.036 +/- 0.023; P = 0.004). Of the patients with ALA, nine had acute disease, and four had been cured of amebiasis 2-8 months previously. There was no significant difference between these two groups in the anti-GIAP sIgA levels. All ALA patients had a high titer serum anti-amebic antibody response, and there was no direct correlation between the level of anti-GIAP salivary IgA and anti-GIAP serum antibodies (R = 0.187). These findings demonstrate that the E. histolytica GIAP is a mucosal antigen in naturally occurring invasive E. histolytica infection.