The retroviral phenomenon of superinfection resistance (SIR) defines an interference mechanism that is established after primary infection, preventing the infected cell from being superinfected by a similar type of virus. This review describes our present understanding of the underlying mechanisms of SIR established by three characteristic retroviruses: Murine

The human genome contains multiple copies of retrovirus genomes known as endogenous retroviruses (ERVs) that have entered the germ-line at some point in evolution. Several of these proviruses have retained (partial) coding capacity, so that a number of viral proteins or even virus particles are expressed under various conditions. Human ERVs (HERVs) belong to the beta-, gamma-, or spuma- retrovirus groups. Endogenous delta- and lenti- viruses are notably absent in humans, although endogenous lentivirus genomes have been found in lower primates. Exogenous retroviruses that currently form a health threat to humans intriguingly belong to those absent groups. The best studied of the two infectious human retroviruses is the lentivirus human immunodeficiency virus (HIV) which has an overwhelming influence on its host by infecting cells of the immune system. One HIV-induced change is the induction of HERV transcription, often leading to induced HERV protein expression. This review will discuss the potential HIV-HERV interactions.Several studies have suggested that HERV proteins are unlikely to complement defective HIV virions, nor is HIV able to package HERV transcripts, probably due to low levels of sequence similarity. It is unclear whether the expression of HERVs has a negative, neutral, or positive influence on HIV-AIDS disease progression. A positive effect was recently reported by the specific expression of HERVs in chronically HIV-infected patients, which results in the presentation of HERV-derived peptides to CD8+ T-cells. These cytotoxic T-cells were not tolerant to HERV peptides, as would be expected for self-antigens, and consequently lysed the HIV-infected, HERV-presenting cells. This novel mechanism could control HIV replication and result in a low plasma viral load. The possibility of developing a vaccination strategy based on these HERV peptides will be discussed.

Different classes of porcine endogenous retroviruses (PERVs), which have the potential to infect humans during xenotransplantation, have been isolated from the pig genome. Because vertebrate genomes may contain numerous endogenous retrovirus sequences, the pig genome was examined for additional endogenous retroviruses, resulting in the isolation of a novel, complete endogenous retrovirus genome, designated PERV-E. The gag, pol and env genes of PERV-E are closely related to those of human endogenous retrovirus (HERV) 4-1, which belongs to the HERV-E family. Results of studies to determine the presence and copy number of PERVs demonstrated that PERV-E and PERV-A/B-like proviruses were present in all genomes tested, but that PERV-C was not found in two of the species examined, including wild boar. Multiple copies of PERVs could be found in each pig genome. Among all of the pig genomes tested, the wild boar genome had the lowest copy number of all PERVs, suggesting that the number of integrations of complete endogenous retroviruses is increased by inbreeding. Xenotransplantation shows great promise for providing a virtually limitless supply of cells, tissues and organs for a variety of therapeutical procedures (Deacon et al., 1997 ; Bengtsson et al., 1998 ; Groth et al., 1994). The tissues and organs of domestic pigs are preferred for xenotransplantation because of their fundamental physiological compatibility with human organs compared to those of other mammals, such as the baboon (van der Kuyl & Goudsmit, 1999 ; Auchincloss & Sachs, 1998). Pigs can be bred and maintained under exogenous-pathogen-free conditions to

The suborder Anthropoidea of the primates has traditionally been divided in three superfamilies: the Hominoidea (apes and humans) and the Cercopithecoidea (Old World monkeys), together comprising the infraorder Catarrhini, and the Ceboidea (New World monkeys) belonging to the infraorder Platyrrhini. We have sequenced an approximately 390-base-pair part of the mitochondrial 12S rRNA gene for 26 species of the major groups of African monkeys and apes and constructed an extensive phylogeny based upon DNA evidence. Not only is this phylogeny of great importance in classification of African guenons, but it also suggests rearrangements in traditional monkey taxonomy and evolution. Baboons and mandrills were found to be not directly related, while we could confirm that the known four superspecies of mangabeys do not form a monophyletic group, but should be separated into two genera, one clustering with baboons and the other with mandrills. Patas monkeys are clearly related to members of the genus Cercopithecus despite their divergence in build and habitat, while the talapoin falls outside the Cercopithecus clade (including the patas monkey).