Patients with autoimmune diseases including systemic lupus erythematosus (SLE) or autoimmune hepatitis (AIH) showed significantly lower number of CD4+ T cells than healthy controls, while the number of CD4+ T cells in patients with rheumatoid arthritis (RA), mixed connective tissue disease (MCTD), Sjögren syndrome (SS), or ulcerative colitis (UC) was normal. Here, CD4 is linked to mixed connective tissue disease.