Bacterial CpG induces hyper-IgM production in CD27(+) memory B cells in primary biliary cirrhosis.
OBJECTIVE
Sera from patients with primary biliary cirrhosis (PBC) are characterized by the presence of antimitochondrial antibodies and elevated levels of immunoglobulin (Ig) M. We hypothesized that the increase in serum IgM is the result of chronic B-cell activation induced via the Toll-like receptor (TLR) signaling pathway.


METHODS
We analyzed peripheral blood mononuclear cells (PBMCs) from patients with PBC and controls following incubation with CpG, a natural ligand for TLR9, and determined the basal and stimulated levels of intracellular IgM, the density of TLR9, and the contribution of specific B-cell subpopulations.


RESULTS
Our data demonstrate uniquely that in vitro incubation of PBMCs from PBC with CpG-B, but not CpG-A, led to a markedly high frequency of intracellular IgM-positive B cells, associated with high levels of synthesized IgM and identified to be a function of CD27(+) memory B cells. This memory B-cell subset also expressed higher densities of TLR9 as compared with naive B cells. These results were not due to increased proliferation, as defined by 5-carboxyfluoresein diacetate succinimidyl ester labeling, or an increase in the life span of B cells, as defined by Bcl-2 expression.


CONCLUSIONS
These findings for the first time identify a major role for innate immune mechanisms in the induction and persistence of abnormal humoral immune responses in PBC.
Kikuchi
Kentaro
K
Division of Rheumatology, Allergy and Clinical Immunology, University of California at Davis, Davis, CA 95616, USA.
Lian
Zhe-Xiong
ZX
Yang
Guo-Xiang
GX
Ansari
Aftab A
AA
Ikehara
Susumu
S
Kaplan
Marshall
M
Miyakawa
Hiroshi
H
Coppel
Ross L
RL
Gershwin
M Eric
ME
D015703:Antigens, CD / Q000097:blood / Q000276:immunology*; D001323:Autoantibodies / Q000097:blood; D001402:B-Lymphocytes / Q000276:immunology*; D015226:Dinucleoside Phosphates / Q000494:pharmacology*; D006801:Humans; D007075:Immunoglobulin M / Q000097:blood*; D007156:Immunologic Memory; D008105:Liver Cirrhosis, Biliary / Q000097:blood / Q000276:immunology*; D008562:Membrane Glycoproteins / Q000097:blood; D008875:Middle Aged; D008928:Mitochondria / Q000276:immunology; D011956:Receptors, Cell Surface / Q000097:blood; D012016:Reference Values; D051217:Toll-Like Receptor 9; D051193:Toll-Like Receptors; D018127:Tumor Necrosis Factor Receptor Superfamily, Member 7 / Q000097:blood*
D015703:Antigens, CD; D001323:Autoantibodies; D015226:Dinucleoside Phosphates; D007075:Immunoglobulin M; D008562:Membrane Glycoproteins; D011956:Receptors, Cell Surface; D051217:Toll-Like Receptor 9; D051193:Toll-Like Receptors; D018127:Tumor Necrosis Factor Receptor Superfamily, Member 7; C495371:TLR9 protein, human; C015772:CpG dinucleotide