Production of interferon-gamma by chicken T cells

In mammals, interferon (IFN)-alpha/beta (type I) is typically resistant to exposure to heat and low pH, whereas IFN-gamma (type II) is labile. Type I IFN has been described in birds; however, the existence of type II IFN has been questioned. We have generated cloned chicken T cell lines that produce high levels of IFN and have studied the physiochemical properties of this IFN activity to determine whether it represents the type I or type II IFN found in mammals. When incubated at 60 degrees C, the IFN activity present in the supernatants from these chicken T cells was found to be labile, two-thirds of the activity being lost within 1-2 minutes. Consistent with IFN-gamma activity, this heat-labile IFN was also sensitive to exposure to pH 2. The heat-resistant IFN lost activity at a much slower rate (half-life > 2 h at 60 degrees C) and was also resistant to exposure to pH 2, which is characteristic of IFN-alpha/beta. To confirm further the presence of IFN-gamma activity, these T cell supernatants were assayed for their ability to activate macrophages as measured by induction of nitrite production. Consistent with mammalian IFN-gamma, the nitrite-inducing activity was found to be heat labile, with over 90% of the activity lost within 5 minutes of heating. These results show that chicken T cells produce IFN-gamma.