Increased Apoptosis of CD20+ IgA+ B Cells is the Basis for IgA Deficiency: The Molecular Mechanism for Correction In Vitro by IL-10 and CD40L

IgA deficiency is the most common primary immunodefi-ciency in humans. Comparative analysis of gene expression in PBMC from IgA-deficient (IgAd) and normal donors us-ing functional multiplex panels showed overexpression of the Caspase-1 (CASP-1) gene. Cells from all the IgAd donors (n = 7) expressed 4–10-fold caspase-1 mRNA over normal controls (n = 5). CD19+ B cells from all IgAd donors produced IgA in cultures following IL-10 and CD40L with Staphylococcus aureus (Cowan) (SAC) or tetanus toxoid (TT) treatments. In CD19+ B cells from IgAd donors, reconstitution of IgA se-cretion was associated with protection of the CD20+ B cell population that underwent apoptosis in the absence of IL-10, CD40L, and TT (triple treatment). Caspase-1 gene expression was decreased in the reconstituted cells. Furthermore, treatment with a caspase-1 inhibitor also independently protected against B cell apoptosis in vitro. An apoptosis-specific cDNA array showed differential expression of 4 out of 96 genes and a shift towards survival-related gene expression from the apoptotic to the protected B cells after triple treatment. There was an increase in the expression of the IAP-2 (inhibitor of apoptosis) gene in the reconstituted cells. Upregulation of the IAP-2 gene protects B cells from deletion and allows for IgA secretion in this system. The inability to detect secreted IgA in IgAd patients could result from the loss of IgA-committed B cells that express high levels of caspase-1