Reduced efficacy of treatment of strongyloidiasis in HTLV-I carriers related to enhanced expression of IFN-γ and TGF-β1

Strongyloidiasis, a human intestinal infection caused by Strongyloides stercoralis (S. stercoralis ), is difficult to cure with drugs. In particular, a decrease of the efficacy of treatment has been reported in patients dually infected with S. stercoralis and human T-cell leukaemia virus type I (HTLV-I), both of which are endemic in Okinawa, Japan. However, the factors influencing this resistance remain unclear. In the present study, patients infected with S. stercoralis , with or without HTLV-I infection, were treated with albendazole, followed up for one year and separated into two groups, cured and non-cured. The cure rate of S. stercoralis was lower in HTLV-I carriers (P<0.05). Serum levels of S. stercoralis-specific IgA, IgE, IgG, IgG1 and IgG4 antibodies were estimated, and a decrease of IgE (P<0.05) and an increase of IgG4 (P<0.05) were observed in the non-cured group, especially in HTLV-I carriers. RT-PCR of cytokines using peripheral blood mononuclear cells revealed that S. stercoralis patients with HTLV-I showed a high frequency of expression of IFN-gamma and TGF-beta1, whereas those without HTLV-I showed no expression of these cytokines. IFN-gamma- and TGF-beta1-positive HTLV-I carriers showed a decrease of IgE (P<0.05), an increase of IgG4 (P<0.01) and a lower cure rate (P<0.01) compared with those who were negative for both cytokines. These results suggest that persistent infection with HTLV-I affected S. stercoralis-specific immunity and reduced therapeutic efficacy.