Interleukin (IL)-15 is an essential cytokine in natural killer (NK) cell development and survival. In humans, IL-15 shows overlapping properties with IL-2 due to partly shared receptors and signal transduction and both cytokines synergize equally well with IL-12 in the induction of interferon (IFN)-γ production from NK cells. Bovine NK cells however, have been reported to produce less IFN-γ after in vitro IL-12 stimulation when exposed to human IL-15 in comparison to bovine IL-2. We therefore wanted to determine if homologous IL-15 is needed for adequate stimulation of bovine NK cells. Biologically active recombinant bovine IL-15 (rbIL-15) produced in mammalian cells by the use of a modified expression vector stimulated NK cells to a dose-dependent IFN-γ production in the presence of IL-12. In contrast to earlier findings, we also detected potent IFN-γ production from bovine NK cells stimulated by human IL-15 and IL-12. Finally, we describe a monoclonal antibody recognizing bovine CD69 and show the expression of this early activation marker on bovine NK cells ex vivo and following rbIL-15 stimulation.
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