Synovial fluid (SF) and peripheral blood (PB) samples from oligo JIA patients and controls were analyzed with flow cytometry to evaluate T cell populations known to provide help to B cells, notably T peripheral helper (Tph, CD4+PD-1hiCXCR5-) and T follicular helper (Tfh, CD4+PD-1+CXCR5+) cells (Figure 1; S1). Here, TPH1 is linked to juvenile idiopathic arthritis.