interleukin secretion trait interleukin-21 secretion trait IL-21 secretion IL21 secretion VT:0009056 Trait.ontology EFO:0801724 Any measurable or observable characteristic related to the controlled release of a pleiotropic cytokine that regulates immunoglobulin production, plasma cell and Th17 T cell differentiation, CD8+ T cell expansion, and inhibits antigen presentation by dendritic cells.