Figure 3.

Neutralization of IL-21-mediated B cell differentiation and IgG1 production. (A) Inhibition of B-cell differentiation to a PC phenotype. A subset of primary human B cells, when cultured for 8 d with 25 ng/mL IL-21, 100 ng/mL anti-CD40 and 10 ng/mL IL-4, differentiate to an IgD^lo, CD38⁺ PC phenotype. Addition of IL-21 neutralizing mAbs (produced from 1^st round hybridoma clones) or soluble IL-21R blocked PC differentiation in a dose-dependent manner. Data for clone 362.78 is shown, though similar results were obtained with clones 362.328 and 366.552. Results shown are representative of two separate experiments. (B) IL-21 mAbs reduced IgG1 production. PC supernatants were collected at the end of the 8 d differentiation period and concentration (ng/mL) of total IgG1 measured. Inhibition of IL-21-mediated PC differentiation by the IL-21 mAbs correlated with a reduction in the amount of IgG1 produced.