CD4 and lymphopenia: We transferred naïve (CD25-CD45RBhi) CD4+ T cells into recombination activating 1 (Rag1)-deficient mice to induce experimental colitis by causing lymphopenia-induced naïve CD4+ T-cell proliferation.32 Compared with those administered wild-type CD4+ T cells, Rag1-deficient mice administered Pank4-deficient CD4+ T cells presented more severe colitis symptoms at the same time points (Fig. 6a-c).