by Human 3 and IgG 1 the Production of IgG Cutting Edge: IL-21 Is a Switch Factor for

IL-21 is a cytokine that regulates the activation of T and NK cells and promotes the proliferation of B cells activated via CD40. In this study, we show that rIL-21 strongly induces the production of all IgG isotypes by purified CD19 (cid:1) human spleen or peripheral blood B cells stimulated with anti-CD40 mAb. Moreover, it was found to specifically induce the production of IgG 1 and IgG 3 by CD40-activated CD19 (cid:1) CD27 (cid:2) naive human B cells. Although stimulation of CD19 (cid:1) B cells via CD40 alone induced (cid:3) 1 and (cid:3) 3 germline transcripts, as well as the expression of activation-induced cytidine deaminase, only stimulation with both anti-CD40 mAb and rIL-21 resulted in the production of S (cid:3) /S (cid:4) switch circular DNA. These results show that IL-21, in addition to promoting growth and differen-tiation of committed B cells, is a specific switch factor for the production of IgG 1 and IgG 3 . The Journal of Immunology, 2004, 172: 5154 –5157.

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