Increased serum IgM, immunodeficiency, and autoimmunity: A clinical series

Primary immunodeficiencies (PIDs) are generally characterized by recurrent infections; however they may be complicated by other clinical disorders such as allergy, autoimmunity, and lymphoproliferation. In particular, autoimmunity may be the first manifestation of the disease in patients with low serum immunoglobulins (Ig) levels. Here we describe a group of patients that share features of immunodeficiency and autoimmunity.

All patients went through a complete T and B cell subset characterization and a B cell function analysis in the peripheral blood by flow-cytometry. B cell proliferation and plasma cell differentiation was measured, in vitro, after CpG stimulation for 7 days as previously described. Semi-quantitative PCR analysis for AID and UNG expression as well as serum levels of BAFF were carried out in order to better define the diagnosis.

Immunological and molecular analysis did not lead to the identification of known molecular defect typical of Hyper IgM syndrome. A comparative study of the peripheral blood B cell subsets between patients and healthy donors showed that in patients with autoimmune manifestations all circulating B cells expressed high amounts of surface IgM.

These results suggest that the increased IgM expression on circulating B cells, reflecting B cell activation, might identify a clinical condition characterized by hyper IgM serum levels of unknown molecular defects, associated with susceptibility to infections and autoimmunity.