IL-21 proliferates and differentiates memory B cells.

Splenocytes from four PRRSV immune and two naïve animals were enriched for CD21⁺ B cells. (A) Cells were labeled with CFSE and then cultured in the presence of CD40L, APRIL, and BAFF with or without IL-21. At day 3 of culture, 1/3 of cells were harvested and evaluated for IC IgG⁺ and CFSE divisions via flow cytometry. (B) PRRSV nsp7 (100,000 live cells/well) and IgG⁺ ELISPOT (10,000 live cells/well) were performed on 1/3 of cultured cells. Following normalization of plated cell number, the proportion of nsp7-specific spots to IgG⁺ spots was calculated and is displayed in (C). The remaining IL-21 treated cells were cultured for a total of 14 days. Supernatants were harvested and evaluated with a limiting dilution nsp7 ELISA. Individual titers are displayed above corresponding columns in (C). Data are representative of two independent experiments with the same animals.