In silico mapping of complex disease-related traits in mice.

Experimental murine genetic models of complex human disease show great potential for understanding human disease pathogenesis. To reduce the time required for analysis of such models from many months down to milliseconds, a computational method for predicting chromosomal regions regulating phenotypic traits and a murine database of single nucleotide polymorphisms were developed. After entry of phenotypic information obtained from inbred mouse strains, the phenotypic and genotypic information is analyzed in silico to predict the chromosomal regions regulating the phenotypic trait.

Identification of complement factor 5 as a susceptibility locus for experimental allergic asthma.

The prevalence and severity of allergic asthma continue to rise, lending urgency to the search for environmental triggers and genetic substrates. Using microarray analysis of pulmonary gene expression and single nucleotide polymorphism-based genotyping, combined with quantitative trait locus analysis, we identified the gene encoding complement factor 5 (C5) as a susceptibility locus for allergen-induced airway hyperresponsiveness in a murine model of asthma. A deletion in the coding sequence of C5 leads to C5-deficiency and susceptibility. Interleukin 12 (IL-12) is able to prevent or reverse experimental allergic asthma. Blockade of the C5a receptor rendered human monocytes unable to produce IL-12, mimicking blunted IL-12 production by macrophages from C5-deficient mice and providing a mechanism for the regulation of susceptibility to asthma by C5. The role of complement in modulating susceptibility to asthma highlights the importance of immunoregulatory events at the interface of innate and adaptive immunity in disease pathogenesis.

Interleukin-6 is required for a protective immune response to systemic Escherichia coli infection.

Interleukin-6 (IL-6) is a multipotential cytokine detected in the serum of patients or experimental animals undergoing bacterial sepsis. To date, the role of IL-6 in gram-negative sepsis models has been controversial. We have used IL-6-deficient mice to investigate the role of IL-6 during virulent Escherichia coli infection and in lipopolysaccharide (LPS)-induced mortality. In this report we describe an increased susceptibility of IL-6-deficient mice to E. coli infection in terms of mortality and accumulation of viable bacteria in tissues, indicating a protective role for IL-6 during the immune response against E. coli. In contrast, mortality rates of IL-6-deficient mice and control animals undergoing LPS-induced shock did not differ, indicating that IL-6 was inconsequential for survival in this model. Furthermore, we have shown that neutrophils were crucial for resistance to E. coli in normal mice. IL-6-deficient mice were unable to efficiently induce neutrophilia in the bloodstream immediately following challenge with E. coli, in contrast to a characteristic neutrophilia induced in control animals. Prophylactic treatment of the mutant animals with recombinant IL-6 protein reverted both the deficit of neutrophilia and the accumulation of bacteria in tissues. These data clarify the role of IL-6 as protective in virulent E. coli infection and suggest that the protective effect may be at least partially mediated through neutrophils.

Interleukin-6-deficient mice are highly susceptible to Listeria monocytogenes infection: correlation with inefficient neutrophilia.

We have produced interleukin-6 (IL-6)-deficient mice to examine, in vivo, the wide variety of biological activities attributed to this multifunctional cytokine. To investigate the role of IL-6 during infectious disease, IL-6-deficient mice were challenged with sublethal doses of Listeria monocytogenes, a facultative intracellular bacterium. While normal control animals were able to clear the infection, mutant animals exhibited a high mortality rate and showed uncontrolled replication of the bacteria in the spleen and liver at 2 and 3 days postinfection. Sections of infected tissues showed an increase in the number and severity of inflammatory foci. All aspects of this phenotype in the mutant animals were completely reverted upon administration of recombinant murine IL-6 (rIL-6). Various parameters of natural killer (NK) cell and macrophage function were unaffected in the challenge of the mutant animals. However, IL-6-deficient animals failed to mount peripheral blood neutrophilia in response to listeriosis, whereas control animals displayed a prominent neutrophilia in the blood at 24 and 48 h postinfection. Additionally, we analyzed the efficacy of rIL-6 in protecting animals devoid of lymphocytes or devoid of neutrophils during listeriosis. Administration of rIL-6 was protective to animals devoid of lymphocytes, suggesting that the rIL-6 protective effect was not mediated through lymphocytes. In contrast, control and mutant animals depleted of neutrophils were refractory to the rIL-6 protective effect. These data suggest that IL-6 is critical early during listeriosis, perhaps acting by stimulating neutrophils either directly or indirectly. Additionally, these data show a promising therapeutic potential for rIL-6 administration during opportunistic infection.

Mice deficient for the IL-3/GM-CSF/IL-5 beta c receptor exhibit lung pathology and impaired immune response, while beta IL3 receptor-deficient mice are normal.

The receptors for IL-3, GM-CSF, and IL-5 share a common beta subunit (beta c), and mice have an additional IL-3 beta subunit (beta IL3). We have independently generated mice carrying null mutations of each molecule. beta c mutant bone marrow showed no response to GM-CSF or IL-5, whereas IL-3 stimulation of beta c or beta IL3 mutant bone marrow was normal. beta c mutant mice showed lung pathology consisting of lymphocytic infiltration and areas resembling alveolar proteinosis, and also exhibited low basal numbers of eosinophils. Infection of beta c mutant mice by Nippostrongylus brasiliensis resulted in the absence of blood and lung eosinophilia. Animals repopulated with beta c mutant bone marrow cells showed slower leukocyte recovery and reduced eosinophil numbers. These data define the role of beta c in vivo, and show a phenotype that is likely to be the cumulative effect of loss of GM-CSF and IL-5 stimulation.