A 22 year follow-up study on lymphatic filariasis in Tanzania: analysis of immunological responsiveness in relation to long-term infection pattern.

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.