604 Phenotypic and Functional Analysis of B Cells in Patients with Common Variable Immunodeficiency

BACKGROUND: Common variable immunodeficiency (CVID) is a primary antibody deficiency characterized by a decrease in antibody production and low or normal B cell numbers. To elucidate the clinical and immunological heterogeneity of this condition, we studied 13 patients diagnosed with CVID, examined the status of B-cell maturation in patients with CVID by analyzing IgD/CD27 expression, and we analyze the in vitro B cell differentiation to plasma cells. METHODS: T, B and NK cell populations was analyzed by flow citometry, expression of CD27 marker was determined to define B cell subsets; we also assessed molecules important for B cell proliferation and differentiation, such as TNFRSF13B (TACI), inducible costimulator (ICOS), CD154, CD20, ICOSL and BAFFR. For B cell differentiation assays, total PBMCs were cultured with CpG alone, or with SAC Cowan, Pokweed and CpG; flow cytometric analysis of plasmablast generation was perfomed after 7 days of culture. RESULTS: Reduced numbers of T and B cells was observed in CVID patients, this reduction was more prominent in adults than in children. One group of 8 patients showed a significant reduction in IgD+CD27+ memory B cells while 3 patients had similar percentage than the healthy control group. The IgD-CD27+ memory B cell population was low in 10 patients (<12%); while it was similar to the healthy control group in 2 of the patients. BAFFR expression in B cells was reduced in 4 patients. Finally, the differentiation to plasmablasts was reduced in patients, stimulation with CpG induced 18.5% of plasmablasts (SD = 12.5%) whereas it was 24% (SD = 8.3%) in healthy controls. CONCLUSIONS: These results suggest that a combined defect in T and B cells may account for CVID, at least in some patients. On the other hand, the complete analysis of markers important for B proliferation and differentiation such as ICOS, CD40, CD154 and TACI can be a useful tool for understanding this heterogeneous disease. B cells from CVID patients fail to progress to IgD-CD27+ memory B cells and plasmablasts. Based on these facts, we hypothesize that one or more crucial signaling molecules is required to induce terminal differentiation into memory B cells, if defective, may cause CVID.