CXCL13 and rheumatoid arthritis: Particular attention is given to the PD-1hi CXCR5− Bcl6low T peripheral helper (Tph) cell population in rheumatoid arthritis, which infiltrates inflamed synovium through expression of chemokine receptors such as CCR2 and augments synovial B cell responses via CXCL13 and IL-21.