C4A and synovial sarcoma: Additionally, we further expanded on previous works by showing how circulating CXCR5+ICOS+PD-1+ Tfh subsets producing high levels of both IL-21 and IFN-γ (including the detection of double IL-21/IFN-γ producers) are selectively enriched in patients with SS with anti-Ro/SSA and anti-La/SSB autoantibodies, positively correlated with IgG levels and negatively with complement C4.