Studies have shown that the severity of COPD is positively correlated with the development of tertiary lymphoid organs (TLOs), and IL-21 T-follicular-helper (Tfh)-like cells have been observed in TLOs of COPD patients, suggesting that Tfh may be involved in the formation of TLOs (50, 51). The gene discussed is IL21; the disease is chronic obstructive pulmonary disease.