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Inflammatory chemokines and their receptors are central to the development of inflammatory/immune pathologies. The apparent complexity of this system, coupled with lack of appropriate in vivo models, has limited our understanding of how chemokines orchestrate inflammatory responses and has hampered attempts at targeting this system in inflammatory disease. Novel approaches are therefore needed to provide crucial biological, and therapeutic, insights into the chemokine-chemokine receptor family. Here, we report the generation of transgenic multi-chemokine receptor reporter mice in which spectrally distinct fluorescent reporters mark expression of CCRs 1, 2, 3, and 5, key receptors for myeloid cell recruitment in inflammation. Analysis of these animals has allowed us to define, for the first time, individual and combinatorial receptor expression patterns on myeloid cells in resting and inflamed conditions. Our results demonstrate that chemokine receptor expression is highly specific, and more selective than previously anticipated.

CXCR2 is an essential regulator of neutrophil recruitment to inflamed and damaged sites and plays prominent roles in inflammatory pathologies and cancer. It has therefore been highlighted as an important therapeutic target. However the success of the therapeutic targeting of CXCR2 is threatened by our relative lack of knowledge of its precise in vivo mode of action. Here we demonstrate that CXCR2-deficient mice display a counterintuitive transient exaggerated inflammatory response to cutaneous and peritoneal inflammatory stimuli. In both situations, this is associated with reduced expression of cytokines associated with the resolution of the inflammatory response and an increase in macrophage accumulation at inflamed sites. Analysis using neutrophil depletion strategies indicates that this is a consequence of impaired recruitment of a non-neutrophilic CXCR2 positive leukocyte population. We suggest that these cells may be myeloid derived suppressor cells. Our data therefore reveal novel and previously unanticipated roles for CXCR2 in the orchestration of the inflammatory response.

El sistema SOS es una respuesta génica global muy extendida dentro del dominio Bacteria que se induce en presencia de lesiones en el DNA y permite la reparación del material genético y la supervivencia celular. La activación del sistema SOS no sólo genera un aumento en la expresión de genes que codifican las proteínas reguladoras del sistema, LexA (represor transcripcional) y RecA (proteína activadora), o de otros genes involucrados en procesos de reparación del DNA, recombinación o inhibición de la división celular. La activación del sistema SOS también está asociada a la expresión de toxinas, la inducción del ciclo lítico de profagos residentes, la expresión y diseminación de resistencias a antibióticos y la transferencia horizontal de islas de patogenicidad y elementos conjugativos. Todo ello sugiere la implicación del sistema SOS en el desarrollo del proceso infectivo. Asimismo, mutantes defectivos en el gen recA de diversos patógenos bacterianos son atenuados, demostrando la importancia de la proteína activadora del sistema en la virulencia. Sin embargo, además de actuar como activadora del sistema SOS, RecA es la principal responsable de los procesos de recombinación homóloga. Esta doble función de la proteína RecA ha impedido establecer si es la incapacidad para inducir la respuesta SOS o la incapacidad para realizar recombinación homóloga la responsable de la atenuación de los mutantes defectivos en recA. Por este motivo, el objetivo principal de este trabajo ha sido determinar el papel del sistema SOS y de la proteína RecA en el proceso infectivo de Salmonella enterica sv. Typhimurium (S. Typhimurium), uno de los principales agentes causales de toxiinfección alimentaria a nivel mundial. Los resultados obtenidos en este estudio demuestran que la sobreexpresión de recA genera un descenso significativo en la capacidad infectiva de este patógeno, lo que indica que durante la infección por S. Typhimurium es necesario el mantenimiento de unos niveles basales de expresión de dicho gen. Asimismo, las pruebas realizadas demuestran que la sobreexpresión de recA genera un descenso en la capacidad para invadir células epiteliales y para traspasar el epitelio intestinal, dos procesos esenciales para que S. Typhimurium pueda establecerse en el intestino y causar infección. De igual modo, este trabajo demuestra que la acumulación de proteína RecA en el interior celular inhibe el movimiento en enjambre (o swarming), un movimiento poblacional sobre superficies semisólidas asociado a la capacidad de numerosos patógenos, entre ellos S. enterica, para invadir tejido epitelial. Esta inhibición tiene lugar a través de la interacción de la proteína RecA con la proteína CheW, implicada en la ruta de señalización de quimiotaxis asociada a este movimiento. Por lo tanto, los resultados de este trabajo añaden el movimiento poblacional a la lista de procesos celulares conocidos que se asocian al sistema SOS y confieren una nueva función a este sistema y a la proteína RecA como reguladores de dicho movimiento en S. Typhimurium. De este modo, la inducción de la respuesta SOS en entornos lesivos para el DNA inhibe el movimiento en enjambre e impide el acercamiento de las células a entornos con concentraciones mayores de compuestos lesivos., The SOS response is a wide-spread regulatory network in the Bacteria domain. Induction of this response occurs in the presence of DNA lesions and it is targeted to address DNA damage and to allow cell survival. The induction of the SOS response causes an increase in the expression of the genes encoding for the system regulatory proteins, LexA (the transcriptional repressor) and RecA (the activator protein), and an increase in the expression of other genes involved in DNA repair processes, homologous recombination and inhibition of cell division. But the induction of the SOS response is also associated with the expression of toxins, the induction of the lytic cicle of resident prophages, the expression and horizontal dissemination of antibiotic resistances, and the horizontal dissemination of pathogenicity islands and integrating conjugative elements. These data suggest that the SOS system plays a key role during the infection process. Moreover, recA mutants of several pathogenic bacteria are avirulent. This demonstrates that the SOS activator is involved in virulence. However, besides acting as the activator of the SOS system, RecA is primarily responsible for the homologous recombination processes. Due to the dual role of the RecA protein, the decrease in virulence of the recA mutants may be attributed either to the reduction of the recombination frequency, or to the inhibition of the SOS system induction, or to both processes. The aim of this work is to elucidate the role developed by the SOS system and by the RecA protein during the infection process of Salmonella enterica sv. Typhimurium (S. Typhimurium), one of the most important pathogens causing foodborne outbrakes in the world. The results obtained in this work show that the overexpression of the recA gene causes a significant decrease in the fitness of this pathogen. Thus, the expression of this gene must remain at its basal level during the infection process developed by S. Typhimurium. Moreover, the overexpression of the recA gene causes a decrease in the ability of this pathogen to invade epithelial cells and to pass through the intestinal epithelium, two essential processes allowing S. Typhimurium to cause the infection. Furthermore, this work demonstrates that the increase in the intracellular concentration of the RecA protein inhibits swarming motility, a multicellular movement over semisolid surfaces associated with the ability of several pathogens, including S. enterica, to invade epithelial cells. This inhibition is caused by the interaction between the RecA protein and the CheW protein, which is associated to the chemotaxis system. The results exposed in this work increase the number of known cellular processes that are associated to the SOS response, conferring a new role on this system and on the RecA protein as regulators of swarming motility in S. Typhimurium. In this context, the induction of the SOS response in the presence of DNA damaging compounds inhibits this kind of motility, avoiding the exposure of the cells to even higher concentrations of such compounds.