Identification of a putative cellular receptor for feline immunodeficiency virus as the feline homologue of CD9.

A monoclonal antibody vpg15 has been identified which recognizes a putative cellular receptor for feline immunodeficiency virus (FIV). The antibody immunoprecipitates a single 24,000 MW species from feline cells. The molecular size and pattern of expression of the ligand for the vpg15 antibody displayed similarities to that of the human leucocyte differentiation antigen CD9. The reactivity of the vpg15 antibody was therefore compared with that of the anti-human CD9 antibody FMC56, an antibody which cross-reacts with feline cells. Expression of the vpg15 ligand correlated well with the reactivity of the FMC56 antibody on peripheral blood leucocytes and a panel of feline cell lines. Furthermore, the anti-human CD9 antibody reacted with murine fibroblast cells which had been transfected with high molecular weight feline DNA and immunoselected with the vpg15 antibody. FMC56 and vpg15 immunoprecipitated a similar 24,000 MW species from surface-iodinated feline cells and depletion of the vpg15 ligand from cell lysates resulted in a corresponding depletion of the FMC56 ligand. The data demonstrate that the vpg15 antibody recognizes the feline homologue of human CD9 and implicate feline CD9 as a cellular receptor for FIV.