Specific functions have been described for 3 members of the family (MS4A1/CD20; MS4A2; MS4A4A) and MS4A1/CD20 has proven to be an invaluable therapeutic target for the treatment of B cell malignancies and autoimmune diseases.9, 11, 12, 13, 15, 17, 25, 26. Here, MS4A4A is linked to autoimmune disease.