SKG CD4+ T cells can transfer arthritis to RAG2‐KO mice.[40] Following a previously established assay, Treg‐depleted SKG T cells (CD4+CD25−) were isolated and transferred to RAG2‐KO mice via retro‐orbital injection.[22] Subsequently, these mice were injected with mannan to induce arthritis. Here, CD4 is linked to arthritic joint disease.