IL6 and viral infectious disease: Thus the combined absence of IL-6 and IL-21 through 8 days post-infection results in a predominantly IL-6 dependent loss of antibody production by the extrafollicular plasma cells (IL-21−/− vs. IL21−/− + αIL-6; P<0.0143; Figure 4B–C), and the absence of germinal center derived plasma cells (IL-21 dependent), resulting in a near complete abrogation of the serum antibody response to the viral infection.