These results suggest that physiological signals that result in strong production of IL4 such as infection with the parasite T. spiralis, can induce the expansion of nTh1 cells in the thymus of WT mice, providing further evidence for the idea that nTh1 cells develop from low affinity TCR interactions in the thymus under normal conditions, and are expanded in the presence of IL4. This evidence concerns the gene NTHL1 and infection.