HISTOPATHOLOGICAL CHANGES IN LYMPH-NODES OF CATS EXPERIMENTALLY INFECTED WITH THE FELINE IMMUNODEFICIENCY VIRUS (FIV)

Twelve specific-pathogen-free (SPF) kittens aged 8-12 weeks were seria lly infected in pairs every 6 weeks, by the intraperitoneal route, wit h the feline immunodeficiency virus (FIV). Three additional SPF kitten s were kept as controls. The infected animals were killed 10 weeks aft er inoculation, during the primary phase of the FIV infection. General ized lymphadenopathy (GL) was observed in the first three pairs of cat s. All lymph nodes examined from the 12 infected cats showed histologi cal changes. These included severe follicular hyperplasia with hyperac tive follicular centres (FCs) which were either (1) naked, (2) infiltr ated by lymphocytes, (3) seen to contain islets of lymphocytic mantle cells, or (4) disrupted by lymphocytes. The presence of both CD4+ and CD8+ T lymphocytes was demonstrated in the FCs immunocytochemically. T he distribution of CD4 lymphocytes resembled that in control lymph nod es, but the CD8 cells were increased in number and either scattered or clustered in the follicles. In addition, varying degrees of interfoll icular proliferation and medullary plasmacytosis were observed in the lymph nodes. These findings, which were common to all infected animals , represented distinct prodromal manifestations of FIV infection. The changes in lymphocyte subpopulation distribution observed in early FIV infection were reminiscent of findings encountered in human immunodef iciency virus (HIV) infection and reinforce the suggestion that FIV in fection is an appropriate model for the study of HIV pathogenesis.