Multivalent cross-linking of membrane Ig sensitizes murine B cells to a broader spectrum of CpG-containing oligodeoxynucleotide motifs, including their methylated counterparts, for stimulation of proliferation and Ig secretion

165

193

Macrophages and B cells are activated by unmethylated CpG-containing sequences in bacterial DNA. The lack of activity of self DNA has generally been attributed to CpG suppression and methylation, although the role of methylation is in doubt. The frequency of CpG in the mouse genome is 12.5% of Escherichia coli, with unmethylated CpG occurring at ∼3% the frequency of E. coli. This suppression of CpG alone is insufficient to explain the inactivity of self DNA; vertebrate DNA was inactive at 100 μg/ml, 3000 times the concentration at which E. coli DNA activity was observed. We sought to resolve why self DNA does not activate macrophages. Known active CpG motifs occurred in the mouse genome at 18% of random occurrence, similar to general CpG suppression. To examine the contribution of methylation, genomic DNAs were PCR amplified. Removal of methylation from the mouse genome revealed activity that was 23-fold lower than E. coli DNA, although there is only a 7-fold lower frequency of known active CpG motifs in the mouse genome. This discrepancy may be explained by G-rich sequences such as GGAGGGG, which potently inhibited activation and are found in greater frequency in the mouse than the E. coli genome. In summary, general CpG suppression, CpG methylation, inhibitory motifs, and saturable DNA uptake combined to explain the inactivity of self DNA. The immunostimulatory activity of DNA is determined by the frequency of unmethylated stimulatory sequences within an individual DNA strand and the ratio of stimulatory to inhibitory sequences.

Section: Discussionmentioning

confidence: 99%

Section: Demethylation Exposes Stimulatory Motifs In Mammalian Dnamentioning

confidence: 99%

mentioning

confidence: 99%

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The Molecular Basis for the Lack of Immunostimulatory Activity of Vertebrate DNA

Stacey

Young

Clark

et al. 2003

165

193

“…The binding of polyvalent Ags stabilizes the surface-signaling microdomains and reduces BCR internalization, which provides a way to enhance BCR signaling and ensure B cell activation in the absence of T cell help. Besides BCR-initiated signaling and signals provided by Th cells, additional signals provided by T cell-independent sources, such as Toll-like receptors and complement receptor CD21, are important for the outcome of Ag-BCR interaction (9,40). These additional signals can be triggered by surface molecules of microbial pathogens, bacterial DNA, and complement factors associated with pathogens.…”

Section: Discussionmentioning

confidence: 99%

Polyvalent Antigens Stabilize B Cell Antigen Receptor Surface Signaling Microdomains

Thyagarajan

Arunkumar

Song

2003

The B cell Ag receptor (BCR) can distinguish subtle differences in Ag structure and trigger differential responses. In this study, we analyzed the effects of Ag valency on the signaling and Ag-targeting functions of the BCR. Although both paucivalent and polyvalent Ags induced the redistribution of the surface BCR into polarized caps, polyvalent Ag-induced BCR caps persisted. Ganglioside GM1, a lipid raft marker, and tyrosine-phosphorylated proteins, but not CD45 and transferrin receptor, were concentrated in BCR caps, suggesting BCR caps as surface-signaling microdomains. Prolonged BCR caps were concomitant with an increase in the level and duration of protein tyrosine phosphorylation and a reduction in BCR internalization and movement to late endosomes/lysosomes. Thus, Ag valency influences B cell responses by modulating the stability of BCR-signaling microdomains and BCR trafficking.

“…The existence of the TLR9-independent pathways in the anti-DNA response has been suggested in several studies. DNA or ODN that do not contain CpG motifs and vertebrate genomic DNA can effectively synergize with specific Ag to costimulate murine B cells, probably via a TLR9-independent way (30,31). Mammalian DNA-Ig complexes, that provide a potent activation of B cells via TLR9, can activate dendritic cells by both TLR9-dependent and -independent pathways (32).…”

Section: Figurementioning

confidence: 99%

Role of TLR9 in Anti-Nucleosome and Anti-DNA Antibody Production in lpr Mutation-Induced Murine Lupus

Lartigue

Courville

Auquit

et al. 2006

144

Systemic lupus erythematosus is characterized by the production of autoantibodies directed against nuclear Ags, including nucleosome and DNA. TLR9 is thought to play a role in the production of these autoantibodies through the capacity of nuclear immunogenic particles to interact both with BCR and TLR9. To determine the role of TLR9 in SLE, C57BL/6-lpr/lpr-TLR9−/− and TLR9+/+ mice were analyzed. The abrogation of TLR9 totally impaired the production of anti-nucleosome Abs, whereas no difference was observed in the frequency of anti-dsDNA autoantibodies whose titer was strikingly higher in TLR9−/− mice. In addition a higher rate of mesangial proliferation was observed in the kidney of TLR9-deficient animals. These results indicate that in C57BL/6-lpr/lpr mice, TLR9 is absolutely required for the anti-nucleosome Ab response but not for anti-dsDNA Ab production which is involved in mesangial proliferation.