Recombinant Rabbit IL-21 Protein

Interleukin‑21 (IL‑21) is an approximately 14 kDa four‑helix‑bundle cytokine in the family of cytokines that utilize the common gamma chain ( gamma_c) as a receptor subunit. gamma_c is also a subunit of the receptors for IL‑2, IL‑4, IL‑7, IL‑9, and IL‑15 (1). IL‑21 is produced by activated T follicular helper cells (Tfh), Th17 cells, and NKT cells (2‑6). It exerts its biological effects through a heterodimeric receptor complex of gamma_c and the IL‑21‑specific IL‑21 R (2, 7). Tfh‑derived IL‑21 plays an important role in the development of humoral immunity through its autocrine effects on the Tfh cell and paracrine effects on immunoglobulin affinity maturation, plasma cell differentiation, and B cell memory responses (4, 8, 9). It is also required for the migration of dendritic cells to draining lymph nodes (10). IL‑21 regulates several aspects of T cell function. It co‑stimulates the activation, proliferation, and survival of CD8⁺ T cells and NKT cells and promotes Th17 cell polarization (3, 5, 6, 11, 12). It blocks the generation of regulatory T cells and their suppressive effects on CD4+ T cells (13, 14). IL‑21 R engagement enhances the cytolytic activity and IFN‑ gamma production of activated NK cells but limits the expansion of resting NK cells (15). In addition, IL‑21 suppresses cutaneous hypersensitivity reactions by limiting allergen-specific IgE production and mast cell degranulation (16). Dysregulation of the IL‑21/IL‑21 R system contributes to the development of multiple immunological disorders (1, 17). The rabbit IL‑21 precursor contains a predicted 135 amino acid (aa) signal sequence and a 133 aa mature chain. Mature rabbit IL‑21 shares 55%‑67% aa sequence identity with mature canine, human, mouse, and rat IL‑21.