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

Abstract

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‐γ and TGF‐β1, whereas those without HTLV‐I showed no expression of these cytokines. IFN‐γ‐ and TGF‐β1‐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.