EFFECTS OF INCIDENTAL INFECTIONS AND IMMUNE ACTIVATION ON DISEASE PROGRESSION IN EXPERIMENTALLY FELINE IMMUNODEFICIENCY VIRUS-INFECTED CATS

Specific pathogen-free cats were experimentally infected with feline i mmunodeficiency virus (FIV) and subsequently exposed to common infecti ous pathogens and immune stimuli over a 3-year period. Cats with preex isting FIV infection showed signs of disease after exposure to Haemoba rtonella felis, Toxoplasma gondii, feline herpesvirus-1, and feline ca licivirus similar to signs in non-FIV-infected cats, although they wer e more severe. No adverse effects of immunization with inactivated rab ies virus vaccine and a synthetic polyproline immunogen were observed in either FIV-infected or non-FIV-infected cats, whereas the applicati on of a diphtheria-tetanus-pertussis vaccine caused transient fever an d lymphadenopathy in both groups of animals. Primary immune responses to pathogens or immunogens were usually delayed or diminished in FIV-i nfected compared with non-FIV-infected cats. Repeated infections and i mmune activation had no significant effects on the levels of FIV-speci fic antibodies or on the proportion of peripheral blood mononuclear ce lls (PBMCs) containing FIV proviral DNA. However, FIV-infected cats th at were not exposed to immune stimuli had lower CD4(+) T-lymphocyte nu mbers and lower CD4(+)/CD8(+) T-lymphocyte ratios at the end of the 3- year study than FIV-infected cats exposed to cofactors. The latter als o had normal levels of interleukin-2 receptor (IL-2R) and major histoc ompatibility class II (MHC-II) antigen expression on PBMCs, while FIV- infected cats not exposed to cofactors had up-regulated IL-2R and down -regulated MHC-II antigen expression. It was concluded that repeated i mmune stimulation did not have a deleterious effect on the course of F IV-induced immunodeficiency.