Guatemalan human onchocerciasis. II. Evidence for IgG3 involvement in acquired immunity to Onchocerca volvulus and identification of possible immune-associated antigens

Ag-specific isotypic differences in immune response to Onchocerca volvulus Ag were assessed for 778 long term residents of endemic Guatemalan areas by quantitative ELISA with 5-min incubation steps and immunoblot. The study population was separated into five groups based on clinical status: N+F+, N+F-, N-F+, N-F-H+, and N-F-H-, where N = O. volvulus adults (nodule), F = microfiladermia, and H = history of O. volvulus infection. A subset of 44 individuals with high exposure to onchocerciasis from the N-F-H- group were critically evaluated and designated as "putatively immune." IgG1 reactivity to O. volvulus Ag was elevated in the majority of infected persons, but not in putatively immune individuals. Specific IgG3 levels, however, were equally elevated in all groups. The majority of N+F- persons also had elevated IgG1 levels, but they were lower than those found in F+ persons. IgG3 reactivities to a group of antigens at 20 kDa (GP20) were seen in many uninfected persons and some N+F- persons. In contrast, most F+ persons, react to this Ag with IgG1 and not IgG3. A mangabey inoculated with the infectious larval stage of O. volvulus (L3), but showed no signs of infection, began to recognize GP20 at 2 wk postinoculation. Early recognition of GP20 was possibly elicited by the larval stage. Purified nodule Ag from N+F+ individuals contained GP20, however, identical nodule Ag prepared from N+F- individuals did not. These data suggest that GP20 Ag may be common to both uterine microfilaria and the infectious larval stages. The fact that GP20 is predominantly recognized by IgG3 in putatively immune persons and some N+F- persons suggests that this increased IgG3 activity may be important in acquired immunity to onchocerciasis.