Abstract The hallmark of T follicular helper (TFH) cells is the ability to help B cells generate humoral immune responses. Recent evidence suggests that aberrant function of TFH cells plays a key role in the generation of autoantibodies, which can inflict autoimmune pathologies. TFH cells are characterized by their unique master regulator (Bcl6), surface marker expression (CXCR5 and ICOS), and production of the pro-inflammatory cytokine interleukin-21 (IL-21). In mice, IL-21 is described as a regulator of TFH cell differentiation and B cell maturation, but its role in human TFH cells remains incompletely understood. In the present study, we sorted TFH subsets from human tonsils or TFH-like cells from human blood to characterize IL-21 production and the functional consequences of blocking IL-21 with a neutralizing antibody. IL-21 was highest in TFHHI cells (CXCR5++ICOS++), detectable in TFHINT cells (CXCR5+ICOS+), and minimal in non-TFH cells. Anti-IL-21 caused a moderate decrease in anti-CD3 stimulated TFH proliferation. Peripheral CXCR5+ TFH-like cells also had elevated IL-21 production, but anti-IL-21 had little effect on TFH-like proliferation. When TFHINT, TFHHI, or TFH-like cells were co-incubated with naïve B cells, anti-IL-21 decreased B cell maturation and Ig production in a dose-dependent manner. Together, these findings indicate that anti-IL-21 inhibits TFH generation and B cell help, and is a promising therapeutic for autoimmune disorders involving autoantibody production.