CD40LG and infection: Moreover, plasma IL-21 concentrations were positively related to the frequencies of Tfh cells, ICOShigh Tfh cells and the OD values of plasma MeV-specific IgM antibodies in the patients with acute-phase MeV infection (Fig. 3c, d, f); however, plasma IL-21 concentrations were not associated with the OD values of plasma MeV-specific IgG antibodies (data not shown).