NKG2D is usually expressed on NK cells, CD8+ T cells but not on CD4+ T cells and interacts with its stress-inducible, major histocompatibility complex class I-chain related ligand (MIC) A and MICB, which are present in the intestinal epithelium [84] and the synovia of RA patients [83]. Here, CD4 is linked to rheumatoid arthritis.