Seventy-one individuals who had been examined for Wuchereria bancrofti microfilaraemia in 1975, some of whom had been offered mass treatment with
diethylcarbamazine (DEC) in subsequent years, were re-identified in 1996 and examined for microfilaraemia, circulating filarial antigenemia and cellular and humoral immunoresponsiveness to crude
antigen homogenates prepared from Brugia pahangi parasite material. 85.9% of the study individuals had the same
infection status in 1975 and 1996, suggesting strong predisposition to
infection over extended periods of time.
IL-4,
IL-5 and IFNγ responses were associated with being
infection negative in 1996 whereas
IL-10 responses were associated with being
infection positive. Similarly, specific
IgG3 and
IgE were strongly associated with being
infection negative in 1996 whereas specific
IgG4, and thus high
IgG4/
IgE ratios, were strongly associated with being
infection positive. Intermediary levels of mainly
IL-5, IFNγ and PBMC stimulation indices were observed for study individuals who changed from being
infection positive in 1975 to
infection negative in 1996, or vice versa, suggesting a transition in cellular immunoresponsiveness associated with changing
infection status. The findings suggest that some people are more disposed to
infection with
bancroftian filariasis than others and that this is largely unaffected by treatment with DEC. The findings also suggest that specific cellular and antibody responses are more related to current than past
infection status, and that
IL-4,
IL-5, IFNγ, specific
IgG3 and
IgE are associated with parasite clearance, whereas
IL-10 and specific
IgG4 are associated with parasite protection.