RAG1 and colitis: For this, unlike previously employed CBir TCR transgenic naive CD4+ T cells that is dependent on flagellin expressing microbial species for inducing colitis (Fig. 5a–g), we used a polyclonal T-cell transfer model of colitis in which naive CD4+ T cells from wild-type (WT) mice are transferred in Rag1−/− lymphodeplete host animals for colitis induction29.