Background RA patients with anti-collagen type II (CII) antibodies have a distinct acute onset phenotype, associated with cytokine induction by surface-bound anti-CII immune complexes (IC). Mononuclear cells and PMN are accumulated both in the synovial fluid and tissue, in close proximity to hyaline cartilage where anti-CII IC might form. Therefore we wanted to investigate to what extent these two cell types cooperate in anti-CII IC induced responses.
Methods Healthy donor granulocytes (PMN) and PBMC were stimulated individually or together (cocultures) with surface-bound IC (anti-CII IC, tetanus toxoid (TT)/anti-TT IC, directly bound IgG), GM-CSF or LPS. Blocking and neutralising studies were performed with antibodies against TLR4, FcgγRIIa, FcgγRIII and GM-CSF. Supernatant cytokine and chemokine levels were analysed with ELISA or ALBIA.
Results Anti-CII IC induced cytokine production by PBMC, whereas PMN alone produced negligible cytokine levels. TNF-aα production was downregulated in all coculture systems compared to PBMC cultures, whereas levels of CXCL8, RANTES and MCP-1 were specifically upregulated in anti-CII IC-stimulated cocultures. The CXCL8 upregulation was dependent on anti-CII IC, as CXCL8 production was downregulated in cocultures stimulated with other IC or LPS. The increase of CXCL8 in anti-CII IC stimulated cocultures was totally dependent on TLR4, partly on PMN enzymes, FcgγRIIa, FcgγRIII, and density of anti-CII in IC. Like anti-CII IC, GM-CSF induced coculture-dependent CXCL8 enhancement, and GM-CSF neutralisation diminished the anti-CII IC-dependent CXCL8 enhancement.
Conclusion In anti-CII-positive RA patients, PMN amplify accumulation of inflammatory cells by inducing chemokines. This mechanism is dependent on TLR4, PMN enzymes, GM-CSF and the joint-specific autoantigen CII. Local TLR4 blockade, PMN enzyme inhibition or GM-CSF neutralisation might be used to suppress acute joint inflammation in early RA.