Production and In Vitro Characterization of Recombinant Chicken Interleukin-2

Mammalian interleukin-2 (IL-2) is a well-characterized cytokine that plays key roles in T cell differentiation and activation, B cell development, and natural killer (NK) cell stimulation. Chicken IL-2, which is the first nonmammalian IL-2 cloned, differs substantially from mammalian IL-2 molecules. We undertook to study the functions of chicken IL-2 by producing recombinant molecules in prokaryotic and eukaryotic expression systems, determining the in vitro properties of these molecules, and examining the kinetics of endogenous IL-2 production in vitro. Recombinant chicken IL-2 (rChIL-2) produced in prokaryotic and eukaryotic expression systems induced proliferation of chicken splenocytes in vitro, demonstrating that glycosylation is not required for this activity. Polyclonal antibodies generated against prokaryotically produced rChIL-2 inhibited proliferation of splenocytes induced by eukaryotically and prokaryotically produced rChIL-2, as well as endogenously produced cIL-2 obtained from ConA-stimulated splenocytes. Human IL-2 or IL-15-induced CTLL proliferation was not blocked by rChIL-2 or polyclonal anti-rChIL-2 antibodies, indicating that chicken IL-2 cannot act as an antagonist of the mammalian IL-2 response. Endogenous chicken IL-2 appears to occur in vitro as a monomer of about 14.2 kDa and is secreted within 4 h after ConA stimulation. The production of rChIL-2 provides us with a useful tool for studying avian immunology as well as a potential vaccine-enhancing agent.