Feline interleukin 2 activity.

The interleukin 2 (IL-2) activity was found in the culture supernatants of feline lymphocytes stimulated with concanavalin A (Con A), as detected by the cell proliferation of a IL-2 dependent murine T cell line (CTLL-2). Feline IL-2 closely resembled rat and human IL-2 in the molecular weight of approximately 16000 daltons, as was estimated from Sephadex G-100 gel filtration chromatography studies. Feline IL-2 was labile to trypsin treatment and was rather sensitive to heating at 70°C for 15 min, the incubation at pH 3.2 and pH 10.5, and the treatment with urea (2, 4 and 8 M), as compared to those of human and murine IL-2. The maximal IL-2 activity in the supernatants from cultures in which lymphocytes were stimulated with Con A (10-100μg/ml) appeared 6-12 hr after initiation of the culture. The addition of exogenous feline IL-2 resulted in the enhanced lymphocyte proliferation in response to Con A, whereas IL-2 alone did not have potent proliferative effect. The feline IL-2 activity was removed by a 4-hr incubation with lymphocytes stimulated with Con A for 48 hr, but not with freshly isolated unstimulated lymphocytes, indicating that the absorption of IL-2 activity results from the binding of IL-2 molecules to IL-2 receptors on Con A-stimulated lymphocytes.