IL21R and infection: To address this issue, we generated mixed bone marrow (BM) chimeras by reconstituting lethally irradiated WT (CD45.1+) mice with a 1∶1 ratio of WT (CD45.1+) and IL-21R−/− (CD45.2+) BM, and evaluated their Treg cell responses to infection with LCMV-DOC.