Increased immunoglobulin A in alcoholic liver cirrhosis: exploring the response of B cells to Toll-like receptor 9 activation

P>Alcoholic liver cirrhosis (ALC) is characterized by increased circulating levels of immunoglobulins (Igs). ALC patients undergo bacterial translocation evidenced by the presence of bacterial DNA in peripheral blood. Bacterial pathogen-associated molecular patterns (PAMPs), such as lipopolysaccharide (LPS), peptidoglycan (PGN) and unmethylated cytosine-guanine dinucleotide (CpG) DNA are ligands of Toll-like receptor (TLR)-4, TLR-2 and TLR-9, respectively. Although TLR activation results generally in the secretion of proinflammatory cytokines, activation of B cells through TLR-7 or TLR-9 is involved in their maturation and Ig synthesis. The aim of the present study was to assess Ig synthesis by ALC B cells under PAMP activation in order to evaluate the possible involvement of TLR pathways in the increased Ig levels, and especially the hyper-IgA observed in ALC. CpG, in combination with interleukin (IL)-10 or IL-21, enhanced IgA, IgG and IgM synthesis by healthy donor (HD) PBMCs, but had only a weak effect on ALC PBMCs. Relative CpG-induced IgA production by purified ALC B cells was less important when compared to HD B cells, in accordance with the lower TLR-9 expression on ALC B cells compared to HD B cells, but the absolute IgA production by CpG-activated B cells was enhanced significantly for ALC when compared to HD, in agreement with their intrinsic ability to produce spontaneously more IgA than HD. LPS and PGN had no direct activity on B cells, whereas R848 also enhanced Ig synthesis, as reported recently. Taken together, these results suggest that TLR priming of B cells could account for the hyperimmunoglobulinaemia observed in ALC patients.