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Salmonellaare intracellular bacteria that are found in the gastrointestinal tract of mammalian, avian, and reptilian hosts. They are one of the leading causes of foodborne infections and a major threat for human populations worldwide. Mouse models have been extensively used to model distinct aspects of the humanSalmonellainfectionsin vivoand have led to the identification of several host susceptibility genes. We have investigated the susceptibility of Collaborative Cross strains to intravenous infection withSalmonellaTyphimurium as a model of human systemic invasive infection. In this model, strain CC042 displayed extreme susceptibility with very high bacterial loads and mortality. CC042 mice showed lower spleen weight and decreased splenocyte numbers before and after infection, affecting mostly CD8+T cells, B cells, and all myeloid populations. Uninfected mice also had lower thymus weight with reduced total number of thymocytes and double negative and (CD4+, CD8+) double positive thymocytes. Analysis of bone marrow resident hematopoietic progenitors showed a strong bias against lymphoid primed multipotent progenitors, which are the precursors of T, B and NK cells. An F2 cross between CC042 and C57BL/6N identified two significant QTLs on chromosome 7 (Stsl6andStsl7) with WSB-derived susceptible alleles. A private variant in the integrin alpha L (Itgal) gene is carried by CC042 in theStsl7QTL region. A quantitative complementation test confirmed the impact ofItgalloss of function in a (C57BL/6JxCC042)F1 background, but not in a C57BL/6J inbred background. These results further emphasize the utility of the Collaborative Cross to identify new host genetic variants controlling susceptibility to infections and improve our understanding of the function of theItgalgene.Author summarySalmonellaare one of the leading causes of foodborne infections and a major threat for human populations worldwide. Not all humans are equally susceptible toSalmonellainfection. Some individuals will develop minor symptoms and recover while others develop severe illness and might die. Mouse models are used to study distinct aspects of humanSalmonellainfectionin vivo. We used a new genetically diverse mouse population to investigate host susceptibility differences toSalmonellainfection. We identified one mouse strain with an extreme susceptibility to infection characterized by very high bacterial loads and mortality. Mice of this strain had small thymus and spleen, two organs which are very important for producing a fully mature immune system. We showed that the strain’s immune response is impaired and that its extreme susceptibility toSalmonellainfection is due to multiple genes defects. We identified a loss-of-function mutation in theItgalgene (Integrin Subunit Alpha L) that plays a central role in the immune response to infection. This gene explains part of the susceptibility and other gene(s) involved remain to be identified. Our results emphasize how new genetically diverse animal models can lead to the identification of new host genetic variants controlling susceptibility to pathogens and improve our understanding of human infections.

Journal URL: http://pubs.acs.org/journals/jmcmar/index.html

Journal URL: http://pubs.acs.org/journals/jmcmar/index.html

A series of β-substituted and β,β-disubstituted N-acyl 5-methoxy-1-methyltryptamines and 5-methoxytryptamines have been prepared as melatonin analogues to investigate the nature of the binding site of the melatonin receptor. The affinity of analogues was determined in a radioligand binding assay using cloned human MT1 and MT2 receptor subtypes expressed in NIH 3T3 cells. Agonist and antagonist potency of all analogues was measured using the pigment aggregation response of a clonal line of Xenopus laevis melanophores, β-Methylmelatonin (17a) and β,β-dimethylmelatonin (17b), though showing a slight decrease in binding at human receptors, show an increase in potency on Xenopus, N-Butanoyl 5-methoxy-1-methyl-β,β-trimethylenetryptamine (12c) is an antagonist at human MT1 receptors but an agonist at MT2, while N-butanoyl 5-methoxy-1-methyl-β,β-tetramethylenetryptamine (13c) is an antagonist at MT1 but had no action at MT2 and is one of the first examples of an MT1 selective antagonist. © 2006 American Chemical Society.

6H-Isoindolo[2,1-a]indoles (5, 7, 10, 13), 5,6-dihydroindolo[2,1- a]isoquinolines (20, 21), and 6,7-dihydro-5H-benzo[c]azepino[2,1-a]indoles (23, 25, 27, 30) have been prepared as melatonin analogues to investigate the nature of the binding site of the melatonin receptor. The affinity of analogues was determined in a radioligand binding assay using cloned human mt1 and MT2 receptor subtypes expressed in NIH 3T3 cells. Agonist and antagonist potency was measured using the pigment aggregation response of a clonal line of Xenopus laevis melanophores. The 2-methoxyisoindolo[2,1- a]indoles (7a-d) showed much higher binding affinities than the parent isoindoles (5a-e), and whereas 7a-c were agonists in the functional assay, 7d and 5a-e were antagonists. The 2-ethoxyisoindolo[2,1-a]indoles (10a-d) showed reduced binding affinities compared to their methoxy analogues, while the 5- chloro derivative 13 showed a considerable reduction in binding affinity and potency compared to 7a. The 10-methoxy-5,6-dihydroindolo[2,1-a]isoquinolines (21a-c) had higher binding affinities than the corresponding parent indoloisoquinolines (20a-c) in the human receptor subtypes, and the parent compounds were antagonists whereas the 10-methoxy derivatives were agonists in the functional assay. The N-cyclobutanecarbonyl derivatives of both the parent (20d) and 10-methoxyl (21d) series had similar binding affinities and were both antagonists with similar potencies. The 11-methoxy-6,7-5H- benzo[c]azepino[2,1-a]indoles (25a-d) had higher binding affinities than the corresponding parent compounds (23a-d) at the MT2 receptor but similar affinities at the mt1 site; all of the compounds were antagonists in the functional assay. Changing 11-methoxy for 11-ethoxy decreased the binding affinity slightly, and this was more evident at the MT2 receptor. All of the derivatives investigated had either the same or a greater affinity for the human MT2 receptor compared to the mt1 receptor (range 1:1-1:132). This suggests that the mt1 and MT2 receptor pockets differ in their ability to accommodate alkyl groups in the indole nitrogen region of the melatonin molecule. Two compounds (7c and 25c) were tested in functional assays on recombinant mt1 and MT2 melatonin receptors. Compound 7c is a potent agonist with some selectivity (44-fold) for the MT2 receptor, while 25c is an MT2-preferring antagonist. Increasing the carbon chain length between N-1 of indole and the 2-phenyl group from n = 1 through n = 3 leads to a fairly regular decrease in the binding affinity, but, remarkably, when n = 3, it converts the methoxy compounds from melatonin agonists to antagonists. The Xenopus melatonin receptor thus cannot accommodate an N-n-alkyl chain attached to a 2-phenyl substituent with n > 2 in the required orientation to induce or stabilize the active receptor conformation.