A new model of outbred genetically selected mice which present a strong acute inflammatory response in the absence of complement component C5.

OBJECTIVE: Mice selected for a strong (AIRmax) or weak (AIRmin) acute inflammatory response present different susceptibilities to bacterial infections, autoimmune diseases and carcinogenesis. Variations in these phenotypes have been also detected in AIRmax and AIRmin mice rendered homozygous for Slc11a1 resistant (R) and susceptible (S) alleles. Our aim was to investigate if the phenotypic differences observed in these mice was related to the complement system. MATERIAL: AIRmax and AIRmin mice and AIRmax and AIRmin groups homozygous for the resistance (R) or susceptibility (S) alleles of the solute carrier family 11a1 member (Slc11a1) gene, formerly designated Nramp-1. METHODS AND RESULTS: While no difference in complement activity was detected in sera from AIRmax and AIRmin strains, all sera from AIRmax Slc11a1 resistant mice (AIRmax(RR)) presented no complement-dependent hemolytic activity. Furthermore, C5 was not found in their sera by immunodiffusion and, polymerase chain reaction and DNA sequencing of its gene demonstrated that AIRmax(RR) mice are homozygous for the C5 deficient (D) mutation previously described in A/J. Therefore, the C5D allele was fixed in homozygosis in AIRmax(RR) line. CONCLUSIONS: The AIRmax(RR) line is a new experimental mouse model in which a strong inflammatory response can be triggered in vivo in the absence of C5.

Resistance to melanoma metastases in mice selected for high acute inflammatory response.

The role of innate immunity in natural resistance to tumor progression was investigated in two mouse lines, AIRmax and AIRmin, selected by bi-directional selective breeding on the basis of high or low acute inflammatory response. Compared with AIRmin, AIRmax mice were shown to be resistant to 7,12-dimethylbenz[a]anthracene (DMBA)/12-O:-tetradecanoylphorbol-13-acetate-induced skin cancers and here we demonstrate that AIRmax are also able to restrain the development of metastases upon transfer of MHC compatible, incompatible or xenogeneic melanomas. An acute inflammatory response to melanoma cells was observed in AIRmax mice only, although both lines were found to mount similar specific immune responses to melanoma antigens. The genetically selected lines therefore represent a model system to analyze the positive correlation between multiple resistance to tumorigenesis and host inflammatory responsiveness.

Effect of genetic modification of acute inflammatory responsiveness on tumorigenesis in the mouse.

Two distinct bidirectional selective breedings for quantitative traits were initiated from identical genetically heterogeneous mouse populations. The resulting lines are characterized by maximal or minimal acute inflammatory responsiveness (AIR): AIRmax and AIRmin lines, respectively, and by resistance or susceptibility to chemical skin tumorigenesis: Car-R and Car-S lines, respectively. The AIR response to s.c. injection of polyacrylamide microbeads, measured by cell content in the local exudate, was 10 times higher in AIRmax than in AIRmin mice. The response to selection was asymmetrical: the realized heritability was 0.26 in AIRmax and 0.008 in AIRmin, and resulted from the additive effect of 7-11 quantitative trait loci (QTL). Low responsiveness was globally dominant in F1 and 48% of F2 segregant variance was found to be due to genetic factors. These findings are the first demonstration of innate regulation of AIR by germ line genes. Susceptibility to skin tumorigenesis induced by a two-stage initiation (DMBA)-promotion (TPA) protocol was lower in AIRmax mice than in AIRmin mice, a 6-fold difference in tumor induction rate. Intense AIR was found to be associated with resistance, and low AIR with susceptibility to tumorigenesis, in F2 segregants chosen for extreme AIR phenotypes. At least some of the AIR QTLs therefore contain genes controlling tumorigenesis. Tumor phenotypes differed more in Car-R and Car-S than in AIRmax and AIRmin lines, indicating that QTLs unrelated to AIR, contribute to the host response to tumorigenesis. The extreme phenotypes/genotypes of the four selected lines and the known genetic constitution of their foundation population, offer new possibilities to discriminate the genes/mechanisms controlling two important traits: AIR and response to chemical tumorigenesis. Collaborative projects will be favorably considered. The description of tumor resistance genes in AIRmax and Car-R mice may be helpful for epidemiology and therapy of human cancer.

Genetics of nonspecific immunity: I. Bidirectional selective breeding of lines of mice endowed with maximal or minimal inflammatory responsiveness.

The genetic regulation of acute inflammatory reaction (AIR) was studied by the method of bidirectional selective breeding, used to produce a line of mice giving the maximal and a line of mice giving the minimal inflammatory reaction (AIR max and AIR min, respectively). The AIR was triggered by subcutaneous injection of a neutral substrate (suspension of polyacrylamide microbeads), and measured by the leukocyte and serum protein accumulation in the exudate. The two parameters are positively correlated and present a normal frequency distribution. The highly genetically heterogeneous foundation population was produced by the equipoised intercrossing of eight inbred strains of mice, and selective breeding carried out by assortative matings of extreme phenotypes. The response to selection in 11 consecutive generations was highly asymmetrical: a marked AIR increase in the AIR max and no change in the AIR min line occurred. The mean value of realized heritability in the AIR max line was 0.26 and 0.18 for cell and protein concentrations, respectively. The response to selection must have resulted from the interaction of seven to nine independent gene loci endowed with additive effects. The lack of response to selection of the AIR min line is discussed. The large inter-line difference opens new possibilities for studying the biochemistry and molecular genetics of inflammation, and also for investigating the beneficial or detrimental effect of inflammatory responses.