Dual requirement of cytokine and activation receptor triggering for cytotoxic control of murine cytomegalovirus by NK cells

Natural killer (NK) cells play a critical role in controlling murine cytomegalovirus (MCMV) and can mediate both cytokine production and direct cytotoxicity. The NK cell activation receptor, Ly49H, is responsible for genetic resistance to MCMV in C57BL/6 mice. Recognition of the viral m157 protein by Ly49H is sufficient for effective control of MCMV infection. Additionally, during the host response to infection, distinct immune and non-immune cells elaborate a variety of pleiotropic cytokines which have the potential to impact viral pathogenesis, NK cells, and other immune functions, both directly and indirectly. While the effects of various immune deficiencies have been examined for general antiviral phenotypes, their direct effects on Ly49H-dependent MCMV control are poorly understood. To specifically interrogate Ly49H-dependent functions, herein we employed an in vivo viral competition approach to show Ly49H-dependent MCMV control is specifically mediated through cytotoxicity but not IFNγ production. Whereas m157 induced Ly49H-dependent degranulation, efficient cytotoxicity also required either IL-12 or type I interferon (IFN-I) which acted directly on NK cells to produce granzyme B. These studies demonstrate that both of these distinct NK cell-intrinsic mechanisms are integrated for optimal viral control by NK cells

Comparison of the pathogenesis of the highly passaged MCMV Smith strain with that of the low passaged MCMV HaNa1 isolate in BALB/c mice upon oronasal inoculation

Murine cytomegalovirus (MCMV) Smith strain is widely used in mouse models to study HCMV infections. Due to high serial passages, MCMV Smith has acquired genetic and biological changes. Therefore, a low passaged strain would be more relevant to develop mouse models. Here, the pathogenesis of an infection with MCMV Smith was compared with that of an infection with a low passaged Belgian MCMV isolate HaNa1 in BALB/c adult mice following oronasal inoculation with either a low (10(4) TCID50/mouse) or high (10(6) TCID50/mouse) inoculation dose. Both strains were mainly replicating in nasal mucosa and submandibular glands for one to two months. In nasal mucosa, MCMV was detected earlier and longer (1-49 days post inoculation (dpi)) and reached higher titers with the high inoculation dose compared to the low inoculation dose (14-35 dpi). In submandibular glands, a similar finding was observed (high dose: 7-49 dpi; low dose: 14-42 dpi). In lungs, both strains showed a restricted replication. In spleen, liver and kidneys, only the Smith strain established a productive infection. The infected cells were identified as olfactory neurons and sustentacular cells in olfactory epithelium, macrophages and dendritic cells in NALT, acinar cells in submandibular glands, and macrophages and epithelial cells in lungs for both strains. Antibody analysis demonstrated for both strains that IgG(2a) was the main detectable antibody subclass. Overall, our results show that significant phenotypic differences exist between the two strains. MCMV HaNa1 has been shown to be interesting for use in mouse models in order to get better insights for HCMV infections in immunocompetent humans

Analysis of hematopoietic stem and progenitor cell populations in cytomegalovirus-infected mice

We have studied the effects of murine cytomegalovirus (MCMV) infection on bone marrow stem and progenitor cell populations to find an explanation for the defects in hematopoiesis that accompany CMV infections in patients. Sublethal MCMV infection of BALB/c mice resulted in a 5- to 10-fold decrease in the numbers of myeloid (colony- forming unit-granulocyte-macrophage [CFU-GM]) and erythroid (burst- forming unit-erythroid [BFU-E]) progenitor cells in the marrow, but not in primitive myeloerythroid progenitor cell (colony-forming unit-spleen [CFU-S]) numbers. In contrast, we observed a 10- to 20-fold reduction in CFU-S as well as CFU-GM and BFU-E in lethally infected mice. Depletion of marrow CFU-GM was less severe in C57BL/10 and C3H/HeJ mice, which are more resistant to the effects of MCMV infection. Treatment of bone marrow cells with MCMV preparations in vitro did not reduce the numbers of CFU-GM, although up to 10% of the cells were productively infected. This finding suggests that CFU-GM were not susceptible to lytic MCMV infection in vitro and are probably not eliminated by lytic infection in vivo. Increases in the frequencies of Sca-1+Lin- marrow cells, a population that includes cells with the characteristics of pluripotential stem cells, were observed in MCMV- infected BALB/c, C57BL/10, and DBA/2J mice. Increases in the frequencies of c-kit+Lin- marrow cells were only seen in DBA/2J mice. MCMV infection did not impair the function of pluripotential stem cells because transplantation of marrow from MCMV-infected donors into irradiated recipient mice resulted in successful reconstitution of the T, B, and myeloid cell lineages.</jats:p

Positional cloning of the murine flavivirus resistance gene

Inbred mouse strains exhibit significant differences in their susceptibility to viruses in the genus Flavivirus, which includes human pathogens such as yellow fever, Dengue, and West Nile virus. A single gene, designated Flv, confers this differential susceptibility and was mapped previously to a region of mouse chromosome 5. A positional cloning strategy was used to identify 22 genes from the Flv gene interval including 10 members of the 2′-5′-oligoadenylate synthetase gene family. One 2′-5′-oligoadenylate synthetase gene, Oas1b, was identified as Flv by correlation between genotype and phenotype in nine mouse strains. Susceptible mouse strains produce a protein lacking 30% of the C-terminal sequence as compared with the resistant counterpart because of the presence of a premature stop codon. The Oas1b gene differs from all the other murine Oas genes by a unique four-amino acid deletion in the P-loop located within the conserved RNA binding domain. Expression of the resistant allele of Oas1b in susceptible embryo fibroblasts resulted in partial inhibition of the replication of a flavivirus but not of an alpha togavirus