Session Title: ACR Plenary Session III: Discovery 2014
Session Type: Plenary Sessions
Individuals with arthritis frequently develop persistent pain despite adequate treatment of synovitis. There is a need to better understand the mechanisms underlying pain occurring with arthritis. Recently, it has been shown that Toll-like receptor 4 (TLR4) mediates the transition from acute to chronic pain in a murine model of arthritis. Rather than developing persistent pain, animals deficient in TLR4 showed an attenuation of the late phase of pain. This receptor is unique in signaling through both MyD88-dependent and independent pathways. In order to further understand the role of TLR signaling, we examined the development of arthritis and persistent pain in mice deficient in these adaptor proteins.
Adult arthritic K/BxN mice were bled and the sera pooled. 100μl of the pooled sera was injected into recipient mice on Days 0 and 2. Clinical arthritis scores and mechanical reactivity, using the up-down method of von Frey testing, were assessed over a period of 28 days in male C57Bl/6, Tlr4-/-, Triflps2, Myd88-/-, Tnf-/–, and Ifnar1-/- mice. Spinal cords were collected from WT and Tlr4-/- arthritic mice and changes in gene expression were measured using nanoString™ nCounter™ analysis. Behavioral data were analyzed using repeated measures ANOVAs, and Duncan New Multiple Range post–hoc analyses when appropriate.
As shown previously, WT mice develop a persistent increase in mechanical reactivity that outlasts the period of inflammation; the 50% withdrawal thresholds dropped from 1.66 at baseline to 0.74 on day 28. In addition, Tlr4-/- mice develop an initial increase in reactivity, which resolves concurrent with inflammation (WT AUC 13.2 and TLR4 AUC 9.7, p<.05). MyD88 and TRIF play distinct roles in the development of pain: mice lacking MyD88 do not develop swelling or allodynia (AUC 2.6, p<0.01), while those deficient in TRIF develop a prolonged allodynia (AUC 12.2), similar to WT animals and outlasting the period of inflammation. NanoString™ nCounter™ analysis of 516 immune genes in the spinal cords of WT and Tlr4-/- mice harvested on Day 10 of arthritis showed differences in expression levels of IL2, RANKL, IFNβ, and TNF transcripts. Therefore, we also examined the development of pain resulting from arthritis in Rag1-/-, Ifnar1-/-, and Tnf-/– mice. In the Tnf-/– mice there was an attenuated development of pain (AUC 8.0, p<.001), the Rag1 (10.0, p<.05) mice developed pain, which resolved with the resolution of inflammation similar to Tlr4-/- mice and Ifnar1-/- mice developed pain that was not different than the WT mice (AUC 12.2).
These results suggest that pain can persist after resolution of inflammation. The innate and adaptive immune systems appear to have distinct roles in the development of the chronic pain state, and this pain cannot be attributed solely to increased TNF or IFNβ transcription.
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/contribution-at-the-spinal-level-of-innate-and-adaptive-immunity-to-the-development-of-persistent-post-inflammatory-mechanical-allodynia-in-arthritic-mice/