Tumor necrosis factor α levels in cats experimentally infected with feline immunodeficiency virus: effects of immunization and feline leukemia virus infection

Abstract

Tumor necrosis factor α (TNFα) levels were determined by enzyme-linked immunosorbent assay (ELISA) and by cell culture bioassay in supernatants of lipopolysaccharide-stimulated feline monocyte cultures and in cat serum samples. There was a good correlation between the results obtained by the two methods. From the fact that TNFα was neutralized quantitatively by antibodies to human TNFα in feline monocyte supernatants and in feline sera, it was concluded that feline TNFα immunologically cross-reacts with human TNFα and that the human TNFα ELISA can be used to quantitate feline TNFα. During the first 6 months after experimental feline immunodeficiency virus (FIV) infection no differences in serum TNFα values were observed between infected and non-infected cats. TNFα levels increased significantly after primary vaccination with a feline leukemia virus (FeLV) vaccine in FIV infected cats over those in the non-infected controls. During secondary immune response TNFα levels rose transiently for a period of a few days in both the FIV positive and the FIV negative cats. After FeLV challenge, TNFα levels increased in all animals challenged with virulent FeLV for a period of 3 weeks. This period corresponded to the time necessary to develop persistent FeLV viremia in the control cats. It was concluded from these experiments that in the asymptomatic phase of FIV infection no increased levels of TNFα are present, similar to the situation in asymptomatic HIV infected humans. Activation of monocytes/macrophages in FIV infected cats by stimuli such as vaccination or FeLV challenge readily leads to increased levels of TNFα.