PTPN22 and infection: Regardless of whether PEP-null mice were fully immune-competent or on a Rag1−/− genetic background, their phenotypes were comparable to PEP-R619W mice after 5e4 PFU infection, but demonstrated increased susceptibility following 1e5 PFU infection and mirrored the outcomes observed in PEP-WT mice (Figs. 1 and 2).