Recombinant Bovine IL-2 Protein

Bovine Interleukin-2 (IL-2) is a 15 kDa, alpha-helical, single chain, potentially glycosylated polypeptide that has potent stimulatory activity for antigen-activated T cells (1 - 5). The molecule is synthesized as a 155 amino acid (aa) precursor that contains a 20 aa signal peptide plus a 135 aa mature segment that is possibly O-glycosylated (4, 5). The mature region has multiple alpha-helices and one intrachain disulfide bond. Mature bovine IL-2 is 64%, 60%, 49%, 50%, 72%, 63% and 67% to mature human, canine, mouse, rat, porcine, equine, and feline IL-2, respectively. Mammalian cells known to express IL-2 include CD4⁺ and CD8⁺ T cells, visceral smooth muscle cells, eosinophils, gamma delta T cells, B cells and dendritic cells. The receptor for IL-2 is complex and consists of three distinct subunits in varying combinations (6, 7). Two of these are ligand-binding and are termed IL-2 R alpha and IL-2 R beta. IL-2 R alpha is 55 kDa and binds IL-2 with low affinity. IL-2 R beta is 75 kDa and binds IL-2 with intermediate affinity. Signal transduction is performed by both IL-2 R beta and a 64 kDa common gamma chain ( gamma_c). This signal transducing common gamma chain does not bind IL-2, but does heterodimerize with IL-2 R beta to form a functional IL-2 receptor. The complex heterotrimeric alpha-beta -gamma c receptor may arise from IL-2 binding to preformed R alpha-R beta complexes (8). Functionally, IL-2 is best known for its autocrine and paracrine activity on T cells. It drives resting T cells into active G1, inducing IL-2 and IL-2 R alpha synthesis and cell proliferation (7). It also promotes Fas-induced death of naïve CD4⁺ T cells, while having minimal effect on activated CD4⁺ memory lymphocytes. Finally, IL-2 seems to play a central role in the expansion and maintenance of CD4⁺ CD25⁺ regulatory T cells. Thus, IL-2 may be a key cytokine in the natural suppression of autoimmunity (9, 10).