Circulating chemokine (C-X-C Motif) receptor 5(+) CD4(+) T cells benefit hepatitis B e antigen seroconversion through IL-21 in patients with chronic hepatitis B virus infection. 
Given the clinical significance of hepatitis B e antigen (HBeAg) seroconversion in chronic hepatitis B virus (HBV) infection, it is critical to elucidate the mechanisms regulating this process.  In the present study, we found that the frequency of circulating chemokine (C-X-C motif) receptor 5 (CXCR5)(+) CD4(+) T cells was higher in patients who had achieved HBeAg seroconversion in both cross-sectional (P < 0.001) and longitudinal (P = 0.009) studies.  These cells were able to produce a significantly higher level of intracellular interleukin 21 (IL-21) after stimulation with HBV peptides in patients with telbivudine-induced HBeAg seroconversion (P = 0.007).  Furthermore, sorted CXCR5(+) CD4(+) T cells from HBeAg seroconverters boosted a higher frequency of antibody against hepatitis B e antigen (anti-HBe)-secreting B cells in coculture assay (P = 0.011).  Of note, the increase in frequency of anti-HBe-secreting B cells was abrogated by soluble recombinant IL-21 receptor-Fc chimera (P = 0.027), whereas exogenous recombinant IL-21 enhanced this effect (P = 0.043).  Additionally, circulating CXCR5(+) CD4(+) T cells shared similar phenotypic markers, and were positively correlated in frequency with, splenic follicular T helper cells.  Circulating CXCR5(+) CD4(+) T cells, by producing IL-21, may have a significant role in facilitating HBeAg seroconversion in patients with chronic HBV infection.