Polyclonal B-cell activation in cats infected with feline immunodeficiency virus

The specificity of the antibody response following natural or experimental infection of domestic cats with feline immunodeficiency virus (FIV) was examined. The antibody response to a range of non-viral antigens, including trinitrophenol (TNP), ovalbumin, beta-galactosidase, deoxyribonucleic acid (DNA) and keyhole limpet haemocyanin (KLH), was measured in 220 cats naturally infected with FIV. Infected cats had higher antibody levels to these antigens, in particular TNP, KLH and beta-galactosidase, than non-infected control cats. Competition binding studies demonstrated that this response was not due to the presence of cross-reacting epitopes on recombinant FIV p17 or p24 antigens, suggesting that the B-cell activation associated with infection was polyclonal rather than entirely virus specific. Studies on cats experimentally infected with FIV revealed a similar pattern, with infected cats developing an antibody response to heterologous non-viral antigens at 6-8 weeks post-infection. There were two discernible peaks of antibody activity, the first occurring 10-20 weeks post-infection and the second peak 40-60 weeks post-infection. The antibody response to KLH, DNA and beta-galactosidase remained elevated throughout the 90-week study period, whereas the antibody levels to the other antigens declined to levels approaching those observed in normal cats.