# Cartilage-binding antibodies induce pain through immune complex-mediated activation of neurons

## TL;DR

This study reveals that cartilage-binding antibodies cause pain through immune complex formation and neuronal activation, independent of inflammation, highlighting a new mechanism for rheumatoid arthritis-associated pain.

## Contribution

It uncovers a novel immune complex-mediated pathway where cartilage antibodies directly activate neurons to induce pain, independent of inflammation.

## Key findings

- Cartilage antibodies induce pain without joint inflammation.
- Neuronal Fc receptors mediate antibody-induced pain.
- Immune complexes directly activate neurons in vitro.

## Abstract

Rheumatoid arthritis-associated joint pain is frequently observed independent of disease activity, suggesting unidentified pain mechanisms. We demonstrate that antibodies binding to cartilage, specific for collagen type II (CII) or cartilage oligomeric matrix protein (COMP), elicit mechanical hypersensitivity in mice, uncoupled from visual, histological and molecular indications of inflammation. Cartilage antibody-induced pain-like behavior does not depend on complement activation or joint inflammation, but instead on tissue antigen recognition and local immune complex (IC) formation. smFISH and IHC suggest that neuronal Fcgr1 and Fcgr2b mRNA are transported to peripheral ends of primary afferents. CII-ICs directly activate cultured WT but not FcR{\gamma} chain-deficient DRG neurons. In line with this observation, CII-IC does not induce mechanical hypersensitivity in FcR{\gamma} chain-deficient mice. Furthermore, injection of CII antibodies does not generate pain-like behavior in FcR{\gamma} chain-deficient mice or mice lacking activating Fc{\gamma}Rs in neurons. In summary, this study defines functional coupling between autoantibodies and pain transmission that may facilitate the development of new disease-relevant pain therapeutics.

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Source: https://tomesphere.com/paper/1908.05298