Analysis of common variable immunodeficiency: approach by memory B cells

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The molecular basis of common variable immunodeficiency ( CVID ) remains unclear. To assess humoral immunity in CVID, we selected 25 patients with early or late onset of disease. X-linked agammaglobulinemia ( XLA ), X-linked hyper-IgM syndrome ( XHIM ) and non-XHIM were excluded based on assessment of the immune response, presence of Bruton's tyrosine kinase ( Btk ) in monocytes or platelets and normal expression of CD40 ligand by activated T cells. The number of circulating B cells was within normal range in all CVTD patients. IgD^- CD27^+ memory B-cells were markedly reduced in all 25 patients and IgD^+ CD27^+ B-cells were diminished in 8 patients. Circulating B cells, including the CVID patients with IgD^+ CD27^+ cells, did not demonstratesomatic hypermutation in immunoglo in immunogioouiin vanaoie ( V )- region genes, similar to cord blood B cells. B cells from CVID patients produced IgM and IgG, but not IgA upon the engagement of Ig receptor and CD40 in the presence of cytokines. B cells from all but 6 patients secreted IgE when stimulated by CD40 crosslinking in the presence of IL-4. The observation of defective memory B cells in CVID demonstrates that naive CVID B cells with or without IgD^+ CD27^+, in analogy to cord blood and hyper IgM syndrome B cells, may be responsible for the failure of the differentiation into plasma cells and the production of high affinity antibodies.