Interleukin 2 (IL-2) is a pleotropic cytokine and well-known as a T cell growth factor in
immunology. It is now known to exert both immunostimulatory and immunosuppressive effects,
optimizing immunological microenvironments for effector and regulatory T cell responses. The
immunomodulatory role of IL-2 is critical for deciding whether or not T cell responses against
specific antigens result in protection. We have established a mammalian cell line (HEK-293) stably
expressing bovine IL-2 (boIL-2) (designated as HEK-293/boIL-2), using the piggyBac transposon
system. The concentration of recombinant bovine IL-2 (rboIL-2) in the culture supernatant of HEK-
293/boIL-2 reached 100 ng/ml on day 7 and showed similar proliferative activity to recombinant
human IL-2 (rhuIL-2) for bovine peripheral mononuclear blood cells. Although rhuIL-2 has been
often used to activate bovine T cells, our results indicate that characteristics of the T cell activation
through rboIL-2 and huIL-2 appear slightly but significantly different. Interestingly, the rboIL-2/
anti-boIL-2 monoclonal antibody (C5) (rboIL-2/C5) complex strongly induced proliferation of
bovine NKp46+cells, natural killer (NK) cells, in vitro. This indicates that the rboIL-2/C5 complex
could function as an IL-2 agonist specifically to increase the NK cell population, which in turn
could enhance the activity of NK cells leading to protective immunity.