| Abstract: | A cell-line, designated LSA-1, was derived from a thymic lymphosarcoma that occurred in a cat with experimentally induced feline leukemia virus (FeLV) infection. LSA-1 cells possessed surface receptors and antigens of normal T-lymphocytes, but were unresponsive to interleukin-2 stimulation. The LSA cell-line was found to constitutively produce and release an interferon into the culture supernatants. Production of this interferon was enhanced in certain clones of the original LSA-1 cell lines. The interferon produced by LSA-1 cells and some of its clones was compared to the standard alpha, beta, and gamma interferons of cats. Unlike alpha and beta interferons, which were acid, SDS, and heat stable, LSA interferon was acid labile and SDS and heat stable. In comparison, standard feline gamma interferon was acid, SDS, and heat labile. LSA interferon had a molecular weight of 20,000 daltons, compared to 17-19,000 daltons for gamma, 19-25,000 for beta, and 25-45,000 daltons for alpha interferons. Standard feline interferons were active only on cat cell lines, with the exceptions of alpha interferon, which also reacted with MDCK canine cells. LSA interferon resembled the standard feline alpha interferon because it also reacted with feline and canine cells. It was concluded that LSA interferon was an atypical acid labile alpha interferon, resembling in this respect the abnormal alpha interferon seen in humans with AIDS and SLE, and mice with retrovirus infections. LSA-1 cells produced high levels of FeLV structural proteins but very little infectious virus. This effect was due to endogenously produced interferon; LSA cell clones that were selected for low interferon production produced much higher levels of infectious FeLV than parent cells or clones selected for high interferon production. Cat cells pretreated with LSA or with standard feline alpha and beta interferons, and then infected with FeLV, produced high levels of FeLV proteins but very little infectious virus. |
