The interferon-inducible p47 (IRG) GTPases in vertebrates: loss of the cell autonomous resistance mechanism in the human lineage
1 Institute for Genetics, University of Cologne, Zülpicher Strasse 47, 50674 Cologne, Germany
2 Eccles Institute of Human Genetics, University of Utah, Salt Lake City, UT 84112-5330, USA
3 Informatics & Systems Groups, Sanger Centre, The Wellcome Trust Genome Campus, Hinxton, Cambridge, CB10 1SA UK
4 Department of Structural Biology, Stanford University Medical School, Stanford, CA 94305, USA
5 Institute for Microbiology and Immunology, University of Cologne Medical School, 50935 Cologne, Germany
Genome Biology 2005, 6:R92 doi:10.1186/gb-2005-6-11-r92Published: 31 October 2005
Members of the p47 (immunity-related GTPases (IRG) family) GTPases are essential, interferon-inducible resistance factors in mice that are active against a broad spectrum of important intracellular pathogens. Surprisingly, there are no reports of p47 function in humans.
Here we show that the p47 GTPases are represented by 23 genes in the mouse, whereas humans have only a single full-length p47 GTPase and an expressed, truncated presumed pseudo-gene. The human full-length gene is orthologous to an isolated mouse p47 GTPase that carries no interferon-inducible elements in the promoter of either species and is expressed constitutively in the mature testis of both species. Thus, there is no evidence for a p47 GTPase-based resistance system in humans. Dogs have several interferon-inducible p47s, and so the primate lineage that led to humans appears to have lost an ancient function. Multiple p47 GTPases are also present in the zebrafish, but there is only a tandem p47 gene pair in pufferfish.
Mice and humans must deploy their immune resources against vacuolar pathogens in radically different ways. This carries significant implications for the use of the mouse as a model of human infectious disease. The absence of the p47 resistance system in humans suggests that possession of this resistance system carries significant costs that, in the primate lineage that led to humans, are not outweighed by the benefits. The origin of the vertebrate p47 system is obscure.