Direct tissue sensing reprograms TLR4+ Tfh-like cells inflammatory profile in the joints of rheumatoid arthritis patients

Amaral-Silva, Daniela; Torrão, Rita C.; Torres, Rita; Falcão, Sandra; Gonçalves, Maria João; Araújo, Maria Paula; Martins, Maria José; Lopes, Carina; Neto, Agna; Marona, José; Costa, Tiago; Castelão, Walter; Silva, Ana Bento; Silva, Inês; Lourenço, Maria Helena; Mateus, Margarida; Gonçalves, Nuno Pina; Manica, Santiago; Costa, Manuela; Pimentel-Santos, Fernando; Mourão, Ana Filipa; Branco, Jaime C.; Soares, Helena

CD4+ T cells mediate rheumatoid arthritis (RA) pathogenesis through both antibody-dependent and independent mechanisms. It remains unclear how synovial microenvironment impinges on CD4+ T cells pathogenic functions. Here, we identified a TLR4+ follicular helper T (Tfh) cell-like population present in the blood and expanded in synovial fluid. Mechanistically, we unveiled that homotypic T-T cell interactions through non-cognate HLA-DR:TCR contacts regulate TLR4 expression on T cells. TLR4+ T cells possess a two-pronged pathogenic activity. Upon TCR and ICOS engagement, TLR4+ T cells produce IL-21, a cytokine known to sponsor antibody production. However, direct TLR4+ engagement on T cells, by endogenous ligands in the arthritic joint, reprograms them towards an IL-17 inflammatory profile compatible with tissue damage program. Blocking TLR4 signaling with a specific inhibitor impaired IL-17 production in response to synovial fluid recognition. Ex vivo, synovial fluid TLR4+ T cells produced IL-17, but not IL-21. TLR4+ T cells appear to uniquely reconcile an ability to promote systemic antibody production with a local synovial driven tissue damage program. TLR4+ T cells could constitute an attractive cellular target and predictive biomarker for erosive arthritis.