PTPRC and infection: Using the Nanostring method, we observed that IL-21 was almost exclusively expressed by mucosal CD4+ T cells (CD45+EpCAM-CD3+CD4+) in WT mice 9 days after C. rodentium infection, while other cells of hematopoietic origin, such as natural killer (NK) cells, dendritic cells (DCs), neutrophils, and macrophages, did not express significant levels of IL-21 transcripts following infection (Fig 2B).