Comparative genomics and host resistance against infectious diseases.

The large size and complexity of the human genome have limited the identification and functional characterization of components of the innate immune system that play a critical role in front-line defense against invading microorganisms. However, advances in genome analysis (including the development of comprehensive sets of informative genetic markers, improved physical mapping methods, and novel techniques for transcript identification) have reduced the obstacles to discovery of novel host resistance genes. Study of the genomic organization and content of widely divergent vertebrate species has shown a remarkable degree of evolutionary conservation and enables meaningful cross-species comparison and analysis of newly discovered genes. Application of comparative genomics to host resistance will rapidly expand our understanding of human immune defense by facilitating the translation of knowledge acquired through the study of model organisms. We review the rationale and resources for comparative genomic analysis and describe three examples of host resistance genes successfully identified by this approach

Immunogenetics of Virus Pathogenesis

Identification of the genetic component of infectious disease susceptibility is an area of intense investigation, which, as presented in this chapter, can provide clues to fundamental questions about virus pathogenesis and the diversity, redundancy, and specialization of host mechanisms against infection. The chapter addresses some methodological approaches of the identification of susceptibility genes to virus infection. It talks about genetic control of virus entry into the host cell. Infection with mouse coronavirus has served as a model to understand the viral and immunological determinants of coronavirus disease, including severe acute respiratory syndrome. Parvovirus B19, a significant human pathogen that causes fetal loss and severe disease in immunocompro‐mised patients, is classified as an erythrovirus due to its ability to infect red blood cell precursors of the bone marrow. Noroviruses or Norwalk‐like viruses are the leading cause of viral acute gastroenteritis in humans. The chapter deals with genetic control of interferon (IFN)‐mediated immunity in viral infection. An important consequence of type I IFN secretion is the activation of natural killer (NK) cells, a central component of the innate response against virus infection. It also discusses major histocompatibility complex (MHC) I alleles and TCR repertoire which can influence CD81 t responses and outcomes after viral infection. Pathogens are considered one of the most powerful forces shaping the evolution of the human genome. Numerous studies have shown that genes or loci involved in host defense against infection present signs of positive or negative selection

Differences in Response Among Inbred Mouse Strains to Infection with Small Doses of Mycobacterium bovis BCG

Intravenous infection of six inbred mouse strains with small doses of dispersed cells of Mycobacterium bovis BCG (15.5 × 10(3) or 15.5 × 10(4) colony-forming units) separated them into resistant (C3H/HeCr, A/J, and DBA/2) and sensitive (B10.A, C57BL/6, and BALB/c) strains as assessed by the magnitude of bacterial multiplication in the spleens at 28 days. The two groups were more sharply separated after infection with the lower dose of BCG (15.5 × 10(3) colony-forming units), which allowed for true multiplication of the bacteria in the spleens of permissive hosts, expressed as the ratio of the number of BCG recovered from the spleens to the number of BCG injected. This coefficient of increase was less than 1 in resistant strains, whereas it was higher than 2.5 in sensitive strains. Significant splenomegaly developed only in mice of the sensitive strains infected with BCG when compared with uninfected controls. There was no correlation between the magnitude of the delayed-type hypersensitivity (DTH) to BCG and susceptibility to infection: DTH was absent in both the sensitive and the resistant strains when the smaller dose of BCG was used for infection. Moreover, significant DTH was detected in animals of the most sensitive (BALB/c) as well as of the most resistant (C3H/HeCr) strain when the higher dose of BCG (15.5 × 10(4)) was used for immunization. These results document significant genetic differences in the ability of inbred mice to inhibit bacterial multiplication after infection with small dispersed doses of BCG. Resistance to BCG multiplication, in this model, does not appear to be related to the establishment of DTH

Characteristics of Mononuclear Phagocytes Mediating Antilisterial Resistance in Splenectomized Mice

The characteristics of mononuclear phagocytes mediating resistance to infection with Listeria monocytogenes during the early phase (up to 48 h) of the response were investigated in mice of the A strain that had undergone splenectomy. Although irradiation in the sham-operated host had no effect on its antilisterial response when administered immediately before infection, it markedly reduced the ability of the splenectomized host to resist listerial challenge. This effect of radiation was demonstrable in the high-dose range (600 r) and could not be reversed immediately by repopulation with 20 × 10(6) syngeneic nucleated bone marrow cells. Administration of silica 24 h before infection profoundly enhanced the growth of L. monocytogenes in the liver of splenectomized mice. Shielding of the liver, but not the bone marrow, protected the splenectomized host against the effects of radiation, indicating that the cell population responsible for mediating the enhanced antilisterial resistance resides in the liver. The enhanced antilisterial resistance of splenectomized mice was specifically because of the absence of the spleen and not merely because of the removal of a favorable replicating environment for listeria organisms

A BALB/c Congenic Strain of Mice That Carries a Genetic Locus (Ity\u3csup\u3er\u3c/sup\u3e) Controlling Resistance to Intracellular Parasites

BALB/c.DBA/2 Idh-1b-Ityr-Pep-3b congenic mice were developed by introgressively backcrossing the Idh-1b and Pep-3b markers of DBA/2 mice onto the BALB/cπ mice. This introduced a 30-centimorgan chromosome 1 segment of DBA/2 chromatin that contained the Ityr gene. BALB/c.DBA/2 Idh-1b-Ityr-Pep-3b mice were resistant to in vivo infections by Salmonella typhimurium, Mycobacterium bovis, and Leishmania donovani

Type I IFN triggers RIG-I/TLR3/NLRP3-dependent inflammasome activation in influenza A virus infected cells.

International audienceInfluenza A virus (IAV) triggers a contagious and potentially lethal respiratory disease. A protective IL-1β response is mediated by innate receptors in macrophages and lung epithelial cells. NLRP3 is crucial in macrophages; however, which sensors elicit IL-1β secretion in lung epithelial cells remains undetermined. Here, we describe for the first time the relative roles of the host innate receptors RIG-I (DDX58), TLR3, and NLRP3 in the IL-1β response to IAV in primary lung epithelial cells. To activate IL-1β secretion, these cells employ partially redundant recognition mechanisms that differ from those described in macrophages. RIG-I had the strongest effect through a MAVS/TRIM25/Riplet-dependent type I IFN signaling pathway upstream of TLR3 and NLRP3. Notably, RIG-I also activated the inflammasome through interaction with caspase 1 and ASC in primary lung epithelial cells. Thus, NS1, an influenza virulence factor that inhibits the RIG-I/type I IFN pathway, strongly modulated the IL-1β response in lung epithelial cells and in ferrets. The NS1 protein derived from a highly pathogenic strain resulted in increased interaction with RIG-I and inhibited type I IFN and IL-1β responses compared to the least pathogenic virus strains. These findings demonstrate that in IAV-infected lung epithelial cells RIG-I activates the inflammasome both directly and through a type I IFN positive feedback loop