Autoimmunity and infection in common variable immunodeficiency (CVID).

Common variable immunodeficiency (CVID) is a heterogeneous group of diseases, characterized by primary hypogammaglobulinemia. B and T cell abnormalities have been described in CVID. Typical clinical features of CVID are recurrent airway infections; lymphoproliferative, autoinflammatory, or neoplastic disorders; and autoimmune diseases among which autoimmune thrombocytopenia (ITP) is the most common. The coexistence of immunodeficiency and autoimmunity appears paradoxical, since one represents a hypoimmune state and the other a hyperimmune state. Considering both innate and adaptive immune response abnormalities in CVID, it is easier to understand the mechanisms that lead to a breakdown of self-tolerance. CD21(low) B cells derive from mature B cells that have undergone chronic immune stimulation; they are increased in CVID patients. The expansion of CD21(low) B cells is also observed in certain autoimmune diseases. We have studied CD21(low) B cells in patients with CVID, CVID, and ITP and with ITP only. We observed a statistically significant increase in the CD21(low) population in the three pathological groups. Moreover, we found statistical differences between the two groups of CVID patients: patients with ITP had a higher percentage of CD21(low) cells. Our data suggest that CD21(low) cells are related to autoimmunity and may represent a link between infection and autoimmunity.