17,19 In the C57BL/6 background, it was even shown that aged μMT animals finally accumulate plasma cells in the MALT despite the apparent absence
of lymphocytes carrying a BCR, suggesting that B-cell progenitors can undergo CSR to IgA and differentiate into IgA-secreting B cells (ASCs) in the absence of mIgM/mIgD.17,18 To date, little is known regarding the potentially specialized function www.selleckchem.com/products/PLX-4032.html of mIgA that could eventually confer specific properties on mucosal or memory mIgA+ cells in comparison with naive mIgM+ cells. It is often assumed that about half of the IgA-producing B cells are involved in T-cell-independent B1 responses, so that alongside the BCR, their development would rely in a large part on signals given by Toll-like receptors and other cytokine receptors in the MALT microenvironment. Cross-linking of mIgA raises the intracellular calcium concentration and supports B-cell
activation so that mIgA+ B cells residing in the MALT can mediate IgA responses to local immunization.20,21 In addition, we have recently shown that replacing IgM expression with IgA expression in naive B cells results in the IgA BCR actively promoting plasma cell differentiation.22 We intended to check whether, as in ε and γ1 chains, expression of the membrane form of the α immunoglobulin heavy chain was required for generating OSI-906 nmr IgA-ASC. This experiment also allowed us to check whether expression of the α class BCR was responsible for the plasma cell accumulation that normally characterizes MALT tissue and if so whether this knock-out would eventually result in the attrition of the gut plasma cell compartment. Consequently, we generated mutant mice in which the membrane exon downstream of the constant α region (Cα) was replaced by a floxed neomycin gene (αΔtail mice). Animal experimentation was in accordance with international guidelines. Etofibrate EIIa-cre transgenic mice were a kind gift from Dr Heiner Westphal, used under a non-commercial research license agreement from Dupont Pharma (Wilmington, DE). The αΔtail construct included an 8-kb α mouse genomic fragment as a 5′ arm
(from a SalI site 3 kb upstream of the Sα region to a HindIII downstream of CH3 secreted-form transcript polyadenylation signal) and a 3 kb long 3′ arm (a genomic fragment originating from downstream of the Cα gene membrane exon). A 1·5-kb NotI–NotI fragment encompassing a neomycin resistance gene flanked by loxP sites was fixed between both arms. E14 ES cells were transfected with linearized vector and selected using G418 (200 μg/ml). Recombinant clones were identified by Southern blot with an external 5′ probe (570 bp, a BamHI/EcoRI fragment located upstream of Sα). After the injection of recombinant ES clones in C57BL/6 blastocysts, the male chimeras were mated with C57BL/6 females and germline transmission of the mutation was checked by Southern blot with an internal probe (500 bp, CH3 fragment, Fig. 1, middle).