Immunological properties of the transmembrane envelope protein of the feline foamy virus and its use for serological screening

The transmembrane envelope (TM) proteins of retroviruses are used as antigen in diagnostic immunoassays and they represent a conserved target for neutralizing antibodies. To analyze the situation in infections with the feline foamy virus (FFV), its recombinant TM protein was produced and used for ELISA and Western blot analyses. Screening sera from 404 German cats showed that 39% reacted against the TM protein, the same infection rate was determined using the Gag protein. Epitope mapping showed antibodies against the membrane proximal external region (MPER) of the TM protein in the sera from infected cats, but attempts to induce neutralizing antibodies by immunization with the recombinant TM protein failed. This is the first report demonstrating that the TM protein of the FFV is highly immunogenic and valuable for serological screening. Similar to HIV-1, but in contrast to different gammaretroviruses, immunization with the TM protein of FFV did not induce neutralizing antibodies.