Bancroftian filariasis: the patterns of filarial-specific immunoglobulin G1 (IgG1), IgG4, and circulating antigens in an endemic community of northeastern Tanzania.

The profile of filarial-specific immunoglobulin G1 (IgG1), IgG4, and Wuchereria bancrofti-specific circulating antigen (Og4C3) was analyzed in individuals one year of age and older in a community with high endemicity for Bancroftian filariasis. The overall microfilarial (mf) prevalence in the examined population was 29%. Fifty-one percent of the population were positive for IgG1 (39% among mf-positive individuals and 63% among mf-negative individuals), whereas 90% were positive for IgG4 (97% among mf-positives and 87% among mf-negatives). The levels of IgG1 and IgG4 were clearly related to mf status and age, but they were unrelated to sex, intensity of microfilaremia, or chronic clinical manifestations. The mean level of IgG1 was significantly higher among amicrofilaremic than among microfilaremic individuals, and it was significantly higher in younger than in older persons. The highest mean IgG4 level was seen in young microfilaremic children, where the level was significantly higher than that in amicrofilaremic children of the same age group and that of older individuals irrespective of mf status. For those 10 years of age and older, the difference in mean level of IgG4 between microfilaremic and amicrofilaremic individuals was not significant. The prevalence of positivity for circulating antigens was 28% in the 1-4-year-old age group, and it increased gradually to 84% in the 50-59-year-old age group (average of 55% for all examined). When analyzed in relation to circulating antigen status, the difference in antibody levels between microfilaremic and amicrofilaremic adults decreased for IgG1 but increased for IgG4, indicating that the IgG1 levels were more related to mf status than to infection status, whereas the IgG4 levels were more related to infection status than to mf status.