Arthritis & Rheumatism, Volume 60,
October 2009 Abstract Supplement
The 2009 ACR/ARHP Annual Scientific Meeting
Philadelphia October 16-21, 2009.
Regulatory Natural Antibodies to Apoptotic Cell Membrane Determinants Inhibit TLR Mediated Activating MAPK Signal Transduction in Dendritic Cells
Silverman, Gregg J., Chen, Yifang
Naturally arising antibodies (NAbs) to apoptotic cell membrane (ACM) determinants, such as phosphorylcholine (PC), can distinguish cells undergoing cell death from healthy cells, and form complexes that have potent properties to downregulate inflammatory responses. By recruitment of early complement factors, C1q and MBL, these NAbs amplify the immunomodulatory properties of ACMs and can inhibit MyD88- and TRIF-dependent TLR signaling in macrophages and dendritic cells (DCs), as well as prevent collagen-induced arthritis. To better understand the signal transduction pathways responsible for these immunosuppressive properties, we have investigated for effects on the Mitogen Activated Protein Kinase (MAPK) system that plays central roles in TLR responses.
Cytokine production and MAPK signaling responses were studied in LPS stimulated murine bone-marrow derived conventional DCs, using standard approaches that include ELISA, Luminex assays, immunoblotting, intracellular flow cytometry and quantitative PCR of transcripts.
We found that a monoclonal IgM anti-PC Mab, but not isotype control, only when co-incubated in serum-free media with purified early complement factors, MBL and C1q, significantly inhibited LPS-induced DC secretion of IL-6, TNFa, IL-12p70, IL-10, IP-10, MCP-1, while there was no induction of TGFb. This anti-ACM NAb also significantly inhibited LPS-mediated phosphorylation of cytoplasmic P38 MAPK, while there was no effect on JNK or ERK1/2. The regulatory NAb also inhibited LPS-mediated phosphorylation of the downstream nuclear transcription factor, ELK. The inhibitory activity of the regulatory NAb on P38 MAPK was comparable to that of dexamethasone, a potent glucocorticoid, which acts in part via transactivation of the dual specificity phosphatase, MKP-1 (also known as DUSP-1 and CL100). Moreover, co-incubation of the anti-ACM NAb with LPS, but not LPS alone, anti-ACM NAb alone, or LPS with isotype control, induced the early (i.e., 10 minute) induction of MKP-1 at a protein and transcript level, while the related MKP-5 was not induced. Intracellular flow cytometric studies confirmed that the NAb, when added to LPS-stimulated DC cultures, rapidly induced MKP-1 levels and suppressed P38 kinase phosphorylation. Studies in MKP-1 deficient cells are currently in progress.
Our studies demonstrate that an IgM regulatory NAb, which forms complexes with ACM and early complement factors to inhibit a broad range of pro-inflammatory TLR responses, can suppress activating P38 MAP kinase responses known to play central roles in inflammatory signal transduction pathways. These studies also provide the first evidence of potentially overlapping pathways responsible for the anti-inflammatory properties of glucocorticoids and regulatory NAbs.
To cite this abstract, please use the following information:
Silverman, Gregg J., Chen, Yifang; Regulatory Natural Antibodies to Apoptotic Cell Membrane Determinants Inhibit TLR Mediated Activating MAPK Signal Transduction in Dendritic Cells [abstract]. Arthritis Rheum 2009;60 Suppl 10 :155