CD4 and granulomatosis with polyangiitis: NKG2D+CD4+ T cells are a novel subset of T lymphocytes reported in many AIDs, such as rheumatoid arthritis, Crohn’s disease and granulomatosis with polyangiitis (GPA) (Wegener’s); these cells interact with NKG2D ligand (NKG2DL)-positive cells, such as synoviocytes, endothelial and epithelial cells.