| Human granulocytic ehrlichiosis (HGE) is an emerging, zoonotic disease caused by a tick-borne, obligate intracellular bacterium, Anaplasma phagocytophila. A. phagocytophila lives and replicates specifically within granulocytes, Nonetheless, pancytopenia is a consistent hallmark of infection. The primary goal of these studies was to understand A. phagocytophila interaction with neutrophils and platelets in light of hematologic abnormalities and in vivo infection kinetics utilizing a murine model of disease.; Laboratory mice show hematologic, immunologic and pathologic responses to infection that mimic infection in human beings. As such, they are useful models to investigate infection kinetics, cellular alterations, and cytokine profiles in the context of an intact host. Quantitative polymerase chain reaction of blood and tissues, flow cytometry and cell sorting of whole blood, in vitro cell culture, histopathology and genetically engineered knockout mice were employed to pursue the specific aims of this thesis.; Chapter one reviews pertinent literature on the pathogenesis of HGE with an emphasis on the mouse model of disease. Chapters two and three evaluate leukocyte interaction with, and response to, A. phagocytophila. The central hypothesis was that during HGE, neutrophils become activated, as evidenced by surface upregulation of the β2 integrin, CD11b/CD18, and this activation alters bacteremia, neutrophil distribution, leukocyte-pathogen extravasation from blood and pathogen acquisition by a tick.; Chapter two delineates the kinetics of CD11b/CD18 upregulation and its effects on leukopenia, pathogen killing and clearance. Data suggest that neutrophil activation is a consistent feature of disease, is associated with the presence of bacteria, is linked to intracellular killing and clearance of infection but does not mediate the leukopenia.; Chapter three focuses on the role of β2 integrins in extravasation and trafficking to sites of dermal inflammation. Results suggest that: (1) infection kinetics and bacteremia are modified by tick-feeding, leukocyte number and the β2 integrins, and (2) significant neutrophil-pathogen trafficking to diverse dermal stimuli and successful pathogen acquisition by ticks occurs in the absence of β2 integrins, although defects are noted.; Chapter four assesses thrombocytopenia in the mouse model of HGE. The role of splenic consumption and immune-mediated destruction were examined as potential mechanisms mediating thrombocytopenia. |
