Expansion and activation of CD4(+)CD25(+) regulatory T cells in Heligmosomoides polygyrus infection

Regulatory T cell responses to infectious organisms influence not only immunity and immunopathology, but also responses to bystander antigens. Mice infected with the gastrointestinal nematode parasite Heligmosomoides polygyrus show an early Th2-dominated immune response (days 7–14), but by day 28 a strongly regulatory profile is evident with antigen-specific IL-10 release and elevated frequency of CD4(+) T cells bearing surface TGF-β. CD4(+)CD25(+) T cells from infected mice show enhanced capacity to block in vitro effector T cell proliferation. CD4(+)CD25(+) cell numbers expand dramatically during infection, with parallel growth of both CD25(+)Foxp3(+) and CD25(+)Foxp3(–) subsets. CTLA-4 and glucocorticoid-induced tolerance-associated receptor, also associated with regulatory T cell function, become more prominent, due to both expanded CD25(+) cell numbers and increased expression among the CD25(–) population. Both intensity and frequency of CD103 expression by CD4(+) T cells rise significantly, with greatest expansion among CD25(+)Foxp3(+) cells. While TGF-β expression is observed among both CD25(+)Foxp3(+) and CD25(+)Foxp3(–) subsets, it is the latter population which shows higher TGF-β staining following infection. These data demonstrate in a chronic helminth infection that Foxp3(+) regulatory T cells are stimulated, increasing CD103 expression in particular, but that significant changes occur to other populations including expansion of CD25(+)TGF-β(+)Foxp3(–) cells, and induction of CTLA-4 on CD25(–) non-regulatory lymphocytes.