Cytokines exert their respective biochemical and physiological effects by binding to specific receptor molecules, which then stimulate signal transduction pathways. Interleukin-21 (IL-21) is a type I cytokine whose receptor is expressed on T, B, and NK cells.

This invention specifically relates to the use of IL-21 to induce differentiation of immature B cells into memory B cells and plasma cells. This invention includes claims of methods for inducing differentiation of a B cell progenitor into memory B cells and/or plasma cells. It also includes claims for enhancing an immune response, treating subjects that lack memory B cells and plasma cells and methods for increasing or decreasing the number of B cells. This invention could conceivably be used in treating or preventing inflammatory disorders, autoimmune diseases, allergies, transplant rejection, cancer, and other immune system disorders.