Abstract. Longitudinal studies are being conducted in Leogane, Haiti to investigate the relationship between acquisition of filarial infection and development of antifilarial immunity as well as the impact of maternal infection on this relationship. Children (0-24 months of age) residing in Leogane were enrolled and were examined periodically to monitor parasitologic status and to collect serum for antigen and antifilarial antibody determinations. To examine the development of filarial antigenemia and antifilarial antibody responses in this cohort, serum samples were selected from a cross section of the population at two (n ϭ 82) and four years of age (n ϭ 76). Antigen prevalence increased from 6% among two-year-olds to more than 30% among four-year-olds, but in only one four-year-old child were microfilaria detected in a 20-l smear. The proportion of antigen-positive children born to antigen-positive mothers was higher than the proportion of antigen-positive children born to antigen-negative mothers (9.8% versus 0% for two-year-olds; P ϭ 0.15; and 39.6% versus 22.7% for four-year-olds; P ϭ 0.18). Antifilarial IgG4 levels were significantly higher among antigen-positive children at both two and four years of age (P Ͻ 0.001). In analyses of paired samples, antifilarial IgG4 responses increased significantly more among children who acquired infection by four years of age than among children who remained antigen negative, whereas antifilarial IgG1 and IgG2 responses changed equally for antigen-positive and -negative children. Antifilarial antibody levels were not influenced by maternal infection status, but were significantly influenced by age, antigen status, and the neighborhood within the community. These results provide evidence that children acquire infection early in life and suggest that antifilarial antibody responses may peak in early childhood.Although antifilarial immune responsiveness is correlated with filarial infection status in humans, 1 it is unclear whether antifilarial immunity directly influences parasitologic or clinical status or merely reflects circulating antigen levels. [2][3][4] Evidence that suggests that immunity does play a pivotal role in determining infection outcome has come from studies of the relationship between filarial infections in mothers and their offspring. Epidemiologic evidence indicates that children of infected mothers are more likely to develop infection than children born to uninfected mothers. 5,6 This increased susceptibility seems to be associated with a persistent change in antifilarial immunity. 7,8 We reasoned that longitudinal studies of the development of antifilarial immunity in a population of children would provide an opportunity to investigate the relationship between antifilarial immunity and acquisition of filarial infection as well as the impact of maternal infection on this relationship. We began studies in Haiti to determine whether the incidence of filarial infection would be higher in children of infected than uninfected mothers and whether antifilar...
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