Demonstration of feline foamy virus in experimentally infected cats by immunohistochemistry

Foamy viruses (FV) are complex retroviruses which are commonly isolated from cats, cattle and non-human primates. The infection is persistent and infected animals have a sustained antibody response. The role of FV in diseases remains unclear, in cats, a possible association with uncharacterized renal symptoms remains to be confirmed. To demonstrate feline FV (FFV) in tissues of experimentally infected cats three polyclonal monospecific antisera from rabbits against three different viral proteins, the structural Gag and the non-structural Bel 1 and Bet proteins were tested for their applicability in immunohistochemistry with paraffin sections. Only the Bet antiserum allowed detection of FFV-specific proteins, the antibodies against Gag and Bel 1 did not work even after pre-treatment of the slides with proteinase K or cooking in a pressure cooking pot. The Bet-reactive antibodies were detected using a commercial streptavidin kit and revealed Bet in the cytoplasm of cells from different lymphoid tissues like lymphnodes, tonsils, thymus and spleen. The method described opens new ways to explore the in vivo replication and tissue specificity of FFV and its possible role in disease.