Analysis of switched memory B cells in patients with IgA deficiency.

Background: Selective IgA deficiency (SIGAD) is the most common primary antibody deficiency, characterized by significant decreased serum levels of IgA in the presence of normal IgG and IgM. Despite several investigations into the nature of the disease, the exact pathophysiology of SIGAD is still unknown.

Methods: In this study, switched memory B cells (CD19+/CD27+/IgD- cell population) of 28 patients with SIGAD and 28 matched healthy controls were investigated using flow cytometry.

Results: The percentage of switched memory B cells in all healthy controls was more than 0.4%. In SIGAD patients, who were classified as group I, the percentage of switched memory B cells was less than 0.4% (0.34 ± 0.06) in 7 patients (25%). The remaining 21 patients were designated as group II (1.74 ± 0.12%). The mean concentration of IgG in group I was significantly lower than in group II (1,014 ± 278 vs. 1,388 ± 406 mg/dl, p = 0.028). Comparison of clinical features between the 2 groups revealed that episodes of pneumonia during the course of disease were significantly higher in group I than in group II (p = 0.002). Autoimmune diseases in group I (57.1%) were also significantly higher (p = 0.01) than in group II (23.8%). The prevalence of bronchiectasis was 57% in group I, while only 1 patient (4.7%) in group II developed bronchiectasis (p = 0.006). Specific antibody deficiency in group I was documented in 5 patients and in group II in 4 patients (p = 0.01).

Conclusions: The classification of SIGAD patients by assessment of switched memory B cells could help physicians with the clinical prognosis for these patients, whereas the patients with reduced switched memory B cells are prone to severe phenotypes.