IGHG3 and in situ carcinoma: Finally, it is possible that the decreased serum IgG2 levels in people with both CIS and MS, increased proportions of IgG3 and IgG1 in people with MS [after adjustment for age, sex, and 25(OH)D], and the inverse correlation of serum IgG3 proportions (%IgG) with time to conversion from CIS to MS may reflect an acquired immunoregulatory defect, similar to that which has been described in chronic human immunodeficiency virus infection (34).