Defective Bcl‐2 expression in memory B cells from common variable immunodeficiency patients

In this study we provide for the first time an analysis of Bcl‐2 levels in various B‐cell subpopulations and antiapoptotic mRNA expression assays after CD40L and IL‐21 stimulation in naïve B cells of CVID patients. B cells from healthy donors presented an increase in Bcl‐2 intracellular expression in the transition from naïve to switched memory B cells. In contrast, this increase was reduced in CVID patients. We found reduced Bcl‐2 protein levels in memory B cells from CVID patients. We further explored the possible alteration of this crucial pro‐survival signalling pathway in CVID patients, by analysing the expression levels of mRNAs from antiapoptotic proteins in naïve B cells, mimicking T‐cell dependent activation in vitro with CD40L and IL‐21. BCL‐XL mRNA levels were decreased, together with reduced levels of AICDA, after naïve B‐cell activation in CVID patients. Our data suggested a molecular mechanism for a tendency toward apoptosis in B cells from CVID patients in relation to NFkB driven transcription. Lower Bcl‐2 protein levels in memory B cells could compromise their long‐term survival, and a possible less activity of NFkB in naïve B cells, munable to increase BCL‐XL mRNA levels, thus not promoting survival in the germinal centers. Summary Common variable immunodeficiency (CVID) is a primary immunodeficiency characterized by hypogammaglobulinemia and different degrees of B cell compartment alteration. Memory B cell differentiation requires the orchestrated activation of several intracellular signaling pathways that lead to the activation of a number of factors, such as nuclear factor kappa B (NF‐κB) which, in turn, promote transcriptional programs required for long‐term survival. The aim of this study was to determine if disrupted B cell differentiation, survival and activation in B cells in CVID patients could be related to defects in intracellular signaling pathways. For this purpose, we selected intracellular readouts that reflected the strength of homeostatic signaling pathways in resting cells, as the protein expression levels of the Bcl‐2 family which transcription is promoted by NF‐κB. We found reduced Bcl‐2 protein levels in memory B cells from CVID patients. We further explored the possible alteration of this crucial prosurvival signaling pathway in CVID patients by analysing the expression levels of mRNAs from anti‐apoptotic proteins in naive B cells, mimicking T cell‐dependent activation in vitro with CD40L and interleukin (IL)‐21. BCL‐