Background/Purpose: Apoptotic cells (AC) have potent anti-inflammatory effects. Injection of apoptotic dendritic cells into mice suppresses the severity of antigen-induced arthritis through increased TGFβ production by resident dendritic cells. However, we have shown that AC that have been previously activated with LPS stimulate a spike in IL-6 production in vivo which inhibits TGFβ and abolishes their immunoregulatory capacity. We set out to define the intrinsic properties of AC that govern their immunomodulatory properties.

Methods: Antigen induced arthritis was used to test the effects of AC in vivo. Peripheral blood samples were obtained from patients with rheumatoid arthritis (all fulfilling ACR criteria) and healthy controls. DNA methylation from human and murine AC was assayed by ELISA and HPLC. We modulated the methylation of AC DNA to determine its role in governing the balance between pro- and anti-inflammatory cytokine production. For some experiments DNA isolated from AC were loaded into liposomes to analyse their properties in vivo. All results refer to murine studies except where specified. 

Results: DNA from activated AC was significantly demethylated compared to resting AC. Demethylation of DNA using 5-azacytidine prior to apoptosis induction abrogated the protective effect of resting AC upon inflammatory arthritis. DNA from resting and activated AC loaded into liposomes had identical effects in vivo as the AC cells themselves. Remethylation of the DNA isolated from activated AC using CpG methylase and loaded into liposomes restored their ability to suppress inflammatory arthritis. Suppression of disease was associated with the production of TGFβ, and reversal of suppression with significantly increased IL-6. Apoptotic CD4+ T cells from patients with rheumatoid arthritis were significantly demethylated compared to healthy controls and led to significantly increased production of IL-6 when cultured with healthy macrophages compared to healthy AC which induced increased TGFβ production.  

Conclusion: Our results reveal that DNA methylation acts as the molecular switch that controls the TGFβ dependent regulatory properties of AC. Activated apoptotic cells by virtue of their hypomethylated DNA induce the production of IL-6, which suppresses TGFβ and promotes a pro-inflammatory milieu. Manipulation of activated AC DNA can restore their protective properties offering novel therapeutic approaches for inflammatory arthritis and other autoimmune rheumatic diseases.

« Back to 2015 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/dna-methylation-governs-the-ability-of-apoptotic-cells-to-suppress-inflammatory-arthritis-via-reciprocal-regulation-of-il-6-and-tgf-beta/