Low-level infection with Trichuris muris significantly affects the polarization of the CD4 response.

Resistance and susceptibility to the intestinal nematode Trichuris muris has been shown to be dependent upon the induction of T helper type 2 (Th2) or Th1 cells, respectively. This study demonstrates that in a normally resistant strain of mouse, i.e. BALB/K which mounts a dominant Th2 response, sub-threshold levels of infection (< 40 eggs) can survive and become sexually mature adult worms (10-20 adults). The immunological basis of this phenomenon was found to be a dramatically altered polarization of the CD4 response. The Th2-response characteristic of this strain of mouse infected with T. muris was shown to be significantly down-regulated as assessed by in vitro cytokine production [interleukin (IL)-4, IL-5 and IL-9]. In contrast, Th1 parameters of infection such as in vitro interferon-gamma production and the presence of parasite-specific IgG2a were greatly up-regulated in these mice.