IL-21 is a type I cytokine that shares the common receptor γ-chain with IL-2, IL-4, IL-7, IL-9, and IL-15. B cells are one of the lymphoid cell types whose development and function are regulated by IL-21. Depending on the interplay with costimulatory signals and on the developmental stage of a B cell, IL-21 can induce proliferation, differentiation into Ig-producing plasma cells, or apoptosis in both mice and humans. Alone and in combination with Th cell-derived cytokines IL-21 can regulate class switch recombination to IgG, IgA, or IgE isotypes, indicating its important role in shaping the effector function of B cells. This review highlights the role of IL-21 in B cell development, function, and disease and provides some perspectives on the future studies in this area.

BACKGROUND:Pediatric endocrinopathies are commonly diagnosed and monitored by measuring hormones of the hypothalamic-pituitary-gonadal axis. Because growth and development can markedly influence normal circulating concentrations of fertility hormones, accurate reference intervals established on the basis of a healthy, nonhospitalized pediatric population and that reflect age-, gender-, and pubertal stage-specific changes are essential for test result interpretation.