To assess whether the colonic lamina propria of SKG mice harbors arthritogenic T cells, we next isolated CD4+ T cells from either the spleen or the colonic lamina propria of prearthritic SKG mice, transferred them into recombination activating gene 2–KO (Rag2-KO) mice, and evaluated arthritis development in recipient mice (Figure 1D). Here, RAG2 is linked to arthritic joint disease.