Tracey C. Dawson, Ph.D.

Dissertation research performed under the guidence of Dr. Nobuyo Maeda

ABSTRACT
    Chemokines constitute a large family of proinflammatory, chemotactic cytokines that mediate their biological functions through binding to seven-transmembrane spanning, G-protein coupled receptors. The primary function of chemokines is to selectively induce chemotaxis and activation of a variety of leukocyte subsets, particulary in inflammatory settings. In order to study the roles of chemokine receptors CCR2 and CCR5 in inflammatory disease, we used conventional gene-targeting to generate three knockout mouse strains which carry deleterious mutations for either the CCR2, CCR5, or DARC gene. Mice deficient in CCR2 exhibited a pronounced defect in macrophage migration as measured by several biological assays. However, initial characterization experiments indicated that CCR5 deficient mice display only modest delays in macrophage accumulation. In contrast, preliminary data suggests that DARC deficiency may actually enhance the normal inflammatory response. In order to define the roles of CCR2 and CCR5 in the development of atherosclerosis, a chronic inflammatory disease, we bred the CCR2 and CCR5 deficient mice onto an apoE deficient background. Atherosclerotic lesion analysis revealed that while the absence of CCR5 does not alter lesion size or plasma lipid levels, the absence of CCR2 causes a marked reduction in lesion size due to defects in macrophage migration. This study confirmed that MCP-1, through its interactions with CCR2, is the primary modulator of atherogenic macrophage chemotaxis. Macrophage and T-lymphocyte activation and migration are key components of the host immune response to influenza virus infections. Histological analysis of lung tissue from influenza infected mice revealed that CCR2 deficiency confers protection from severe tissue damage at early time points due to delays in initial macrophage accumulation, suggesting that macrophage migration in this model is normally mediated by MCP-1/CCR2 interactions. In contrast, CCR5 deficient mice displayed increased mortality with early severe tissue damage caused by the massive accumulation of macrophage in the infected lungs. This phenotype was likely caused by the altered chemokine expression patterns that were revealed by RT-PCR analysis of infected CCR5 deficient lungs. The chemokine receptor knockout mice generated in our laboratory will provide a useful tool for studying the in vivo effects of chemokines and chemokine receptors on host response.