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

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

Transspecies Transmission of the Endogenous Koala Retrovirus

ABSTRACT The koala retrovirus (KoRV) is a gammaretrovirus closely related to the gibbon ape leukemia virus and induces leukemias and immune deficiencies associated with opportunistic infections, such as chlamydiosis. Here we characterize a KoRV newly isolated from an animal in a German zoo and show infection of human and rat cell lines in vitro and of rats in vivo, using immunological and PCR methods for virus detection. The KoRV transmembrane envelope protein (p15E) was cloned and expressed, and p15E-specific neutralizing antibodies able to prevent virus infection in vitro were developed. Finally, evidence for immunosuppressive properties of the KoRV was obtained.

Mutational Analysis of the Fusion Peptide of Moloney Murine Leukemia Virus Transmembrane Protein p15E

ABSTRACT Fusion peptides are hydrophobic sequences located at the N terminus of the transmembrane (TM) envelope proteins of the orthomyxoviruses and paramyxoviruses and several retroviruses. The Moloney murine leukemia virus TM envelope protein, p15E, contains a hydrophobic stretch of amino acids at its N terminus followed by a region rich in glycine and threonine residues. A series of single amino acid substitutions were introduced into this region, and the resulting proteins were examined for their abilities to be properly processed and transported to the cell surface and to induce syncytia in cells expressing the ecotropic receptor. One substitution in the hydrophobic core and several substitutions in the glycine/threonine-rich region that prevented both cell-cell fusion and the transduction of NIH 3T3 cells when incorporated into retroviral vector particles were identified. In addition, one mutation that enhanced the fusogenicity of the resulting envelope protein was identified. The fusion-defective mutantstrans dominantly interfered with the ability of the wild-type envelope protein to cause syncytium formation in a cell-cell fusion assay, although no trans-dominant inhibition of transduction was observed. Certain substitutions in the hydrophobic core that prevented envelope protein processing were also found. These data indicate that the N-terminal region of p15E is important both for viral fusion and for the correct processing and cell surface expression of the viral envelope protein.