Pathogenesis of relapsing polychondritis: A 2013 update

Relapsing polychondritis (RP) is a systemic inflammatory disease primarily affecting not only the cartilaginous structures of the ears, nose and tracheobronchial tree but also the joints, the inner ear, the eyes, and the cardiovascular system. RP is an immune-mediated disease during which target antigens are still unknown, but data from human studies and murine models strongly support a role of both Collagen Type II (CII) and matrilin-1 as potential candidates. RP is likely a Th1-mediated disease as serum levels of interferon (IFN)-γ, interleukin [IL]-12, and IL-2 parallel changes in disease activity, while the levels of Th2 cytokines do not. Serum levels of sTREM-1, interferon-γ, CCL4, vascular endothelial growth factor, and matrix metalloproteinases-3 are significantly higher in RP patients than in healthy donors, with sTREM-1 correlating with disease activity. Patients with active RP also have significantly higher levels of MCP-1, MIP-1β, MIF, and IL-8 than controls. These pro-inflammatory chemokines are involved in the modulation and recruitment of monocytes and neutrophils. Altogether, these data suggest that a complex cytokine network orchestrates the recruitment of infiltrating cells in RP lesions. Cytokine modulation using TNFα blockers, rituximab, anakinra, tocilizumab, and abatacept has recently been shown effective in some RP cases but further data are needed. Better understanding of the repertoire of infiltrating cells may provide interesting clues to further define the putative RP auto-antigens. Study of circulating mononuclear cells during RP flares may also provide crucial information about the ongoing cellular trafficking and recruitment processes involved in this rare disease.