Acquisition and expression of humoral reactivity to antigens of infective stages of filarial larvae

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Abstract
Measurement of anti-larval responses in filaria-exposed populations may shed light on the natural history of exposure to Wuchereria bancrofti. Using serum samples obtained by a cross-sectional survey of 172 individuals from two neighbourhoods in Leogane, Haiti, antibody responses directed against infective stage filarial larvae (L3) were assayed by enzyme-linked immunosorbent assay (ELISA), immunofluorescence (IFA), and immunoblot for the presence of anti-larval antibodies. ELISA results indicated that virtually all members of both neighbourhoods mounted an anti-larval antibody response within the first five years of life, suggesting that exposure to infection is universal. In a multiple linear regression analysis that modelled antibody levels as a function of age, gender, microfilaria status, and neighbourhood (as a proxy for transmission intensity), isotype-specific antibody levels were found to be significantly influenced by both age and neighbourhood. Antibodies directed against the surface of L3 also were age-dependent; the prevalence of IgG antibodies detected by IFA was significantly higher in children than in adults. The prevalence of antibody recognition of 16.7 and 72.3 kDa L3 antigens on immunoblots was significantly greater for serum samples from microfilaraemic than amicrofilaraemic persons. These results suggest that antibody responses to larval antigens are influenced to varying degrees by age, transmission intensity, and microfilaraemia status.