CVID-Associated B Cell Activating Factor Receptor Variants Change Receptor Oligomerization, Ligand Binding and Signaling Responses

Abstract

Purpose B cell activating factor (BAFF) binding to BAFF-receptor(BAFFR) activates essential cellular functions required forthe survival of mature, human B cells. Thus,deletion ofthe BAFFR gene blocks the development of B cells at the transition from immature to mature B cells resulting in B lymphopenia and hypogammaglobulinemia. In addition to complete BAFFR deficiency, single nucleotide variants changing the primary amino acid sequence of BAFFR gene exist. Some of these variants were foundin patients suffering from immunodeficiency, autoimmunity, or B cell lymphomas. However, it remains unclearto which extent such variants disturb the activity of BAFFR. Methods Since individual differences and genetic/environmental modifiers change the expression and activity of BAFFR, we developed a cellular system that allows the unbiased analysis of BAFFR variants P21R, A52T, G64V, Dup92-95, P146S, and H159Y regarding oligomerization, signaling, and ectodomain shedding.Results Here we show that several of these variants impair BAFFR oligomerization, direct interactions between BAFFR and the B cell receptor component CD79B, BAFFR ectodomain shedding and the activation of AKT and ERK1/2. Conclusion All of these variants are pathogenic and have the potential to contribute to the development of primary antibody deficiencies, autoimmunity and lymphoma, but they most likely do not cause B lymphopenia and agammaglobulinemia like complete BAFFR deficiency.