Lack of antibody response in pigs immunized with the transmembrane envelope protein of porcine endogenous retroviruses

Recently we immunised different mammalian species (goats, mice, rats, rabbits, guinea pigs, hamsters) with the recombinant ectodomain of the transmembrane envelope (TM) protein p15E of the porcine endogenous retrovirus (PERV). In all cases, neutralising immune sera were induced, which recognised epitopes in the fusion peptide proximal region (FPPR) and the membrane proximal external region (MPER) of p15E. In order to analyse whether pigs are also able to produce such antibodies, and whether such antibodies can be used to study involvement of the TM protein in placenta development (as was shown for endogenous retroviruses of other species), German landrace pigs were immunised with p15E of PERV. But no binding and neutralising antibodies were produced as shown in three Western blot analyses and in a neutralisation assay, indicating that pigs are tolerant to their endogenous retroviruses at least for the ectodomain of the TM protein.