Parasitic nematodes typically modulate T-cell reactivity, primarily during the chronic phase of infection. We analyzed the role of CD4-positive (CD4+) T effector (Teff) cells and regulatory T (Treg) cells derived from mice chronically infected with the intestinal nematode Heligmosomoides polygyrus. Different CD4+ T-cell subsets were transferred into naïve recipients that were subsequently infected with H. polygyrus. Adoptive transfer of conventional Teff cells conferred protection and led to a significant decrease in the worm burdens of H. polygyrus-infected recipients. Roughly 0.2% of the CD4+ T cells were H. polygyrus specific based on expression of CD154, and cells producing interleukin 4 (IL-4) and IL-13 were highly enriched within the CD154+ population. In contrast, adoptive transfer of Treg cells, characterized by the markers CD25 and CD103 and the transcription factor Foxp3, had no effect on the worm burdens of recipients. Further analysis showed that soon after infection, the number of Foxp3+ Treg cells temporarily increased in the inflamed tissue while effector/memory-like CD103+ Foxp+ Treg cells systemically increased in the draining lymph nodes and spleen. In addition, Treg cells represented a potential source of IL-10 and reduced the expression of IL-4. Finally, under in vitro conditions, Treg cells from infected mice were more potent suppressors than cells derived from naïve mice. In conclusion, our data indicate that small numbers of Teff cells have the ability to promote host protective immune responses, even in the presence of Treg cells.
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