In this project we are building a mathematical model to track the movement of spermatozoa during the process of chemotaxis. Our model is built on an off-lattice spherical biased random walk in 3-dimensional space, an extension of previous conventional deterministic 2-dimensional models. The sperm's type of movement is decided based on a comparison of the current and previous chemoattractant concentration which can be used to see whether it is approaching the egg. From the statistical analysis of the simulation results, we find that chemotaxis is an effective mechanism to increase the number of sperm reaching the egg.

A Hodgkin-Huxley style system of ODEs was developed to model the ion channel activity of A. punctulata sperm flagellum during exposure to resact during chemotaxis. Empirical data was used in conjunction with parameter estimation methods in an attempt for the model to reproduce realistic Voltage potentials and ion concentrations. The change in calcium concentration is of particular interest, as it is essential in the waveform of the flagellum during chemotaxis.

Helicobacter pylori is a human pathogen that colonizes the stomach and increases the risk of diseases such as ulcers and gastric cancer. The distribution of H. pylori within the stomach is associated with different disease outcomes, with more dispersed colonization correlated with gastric cancer. The focus of this research is to study the chemotactic responses that promote dispersal of H. pylori within the stomach. We have shown previously that H. pylori perceive the quorum signal autoinducer-2 (AI-2) as a chemorepellent. We report that H. pylori chemorepulsion from endogenous AI-2 influences the proportion and spatial organization of cells within biofilms. Strains that fail to produce AI-2 (∆luxS) or are defective for chemotaxis (∆cheA) formed more spatially homogenous biofilms with a greater proportion of adherent versus planktonic cells than wildtype biofilms. Reciprocally, a strain that overproduced AI-2 (luxSOP) formed biofilms with proportionally fewer adherent cells. Along with the known AI-2 chemoreceptor, TlpB, we identified and characterized two novel periplasmic binding proteins, AibA and AibB, that independently both bind AI-2 and are required for the AI-2 chemorepulsion response. Disruptions in any of the proteins required for AI-2 chemotaxis recapitulated the biofilm adherence and spatial organization phenotype of the ∆luxS mutant. Furthermore, exogenously administered AI-2 was sufficient to decrease the proportion of adherent cells in biofilms and promote dispersal of cells from biofilms in a chemotaxis dependent manner. Finally, we found that disruption of AI-2 production or AI-2 chemotaxis resulted in increased clustering of cells in microcolonies on cultured epithelial cells. We conclude that chemotaxis from AI-2 is a determinant of H. pylori biofilm spatial organization and dispersal and may play an important role in H. pylori colonization of the stomach by promoting dispersal away from areas of high cell density, thereby modulating the disease spectrum of the host. This dissertation contains previously unpublished co-authored material.

The chemokine receptor CXCR3 and its agonists CXCL9/Mig, CXCL10/IP-10 and CXCL11/I-TAC are involved in a variety of inflammatory disorders including multiple sclerosis, rheumatoid arthritis, psoriasis and sarcoidosis. CXCL11 has also been reported to bind to an additional receptor, namely CXCR7, which also interacts with CXCL12. Two alternatively spliced variants of the human CXCR3 receptor have been described, namely CXCR3-B and CXCR3-alt. The human CXCR3-B has been found to bind CXCL9, CXCL10, CXCL11 as well as an additional agonist CXCL4/PF4. In contrast, CXCR3-alt only binds CXCL11. This work demonstrates that CXCL4 like the original CXCR3 agonists is capable of inducing biochemical signalling, namely intra-cellular calcium elevation, and activation of p44/p42 MAPK and PI3K/Akt pathways in activated human T lymphocytes. Phosphorylation of p44/p42 MAPK and Akt was inhibited by pertussis toxin, suggesting coupling to Gi protein. In contrast CXCR3 antagonists blocked CXCR3 agonists but not CXCL4-mediated responses. Surprisingly, stimulation of T cells with CXCL4 failed to elicit migratory responses of these cells and did not lead to loss of surface CXCR3 expression. Collectively our evidence shows that although CXCL4 is coupled to downstream biochemical machinery, its function in T cells is distinct from the function of CXCR3 agonists. The work presented in this thesis also indicates that despite considerably lower surface expression in comparison to the full length CXCR3, CXCR3-B and CXCR3-alt transduce biochemical signals in response to CXCL11 in transfected cells. According to previous reports the role of CXCR7 in signalling and chemotaxis in T cells could not be detected. In T cells and transfected cells system CXCR7 was localised at the plasma membrane and was efficiently internalized in response to CXCL11 and CXCL12. Studies of the involvement of methylation in T cell chemotaxis suggest that this modification may be required in this process as it was partially inhibited by methylation inhibitor- MTA. Moreover T cell co-stimulation caused increased levels of arginine mono-methylated proteins suggesting the importance of methylation in T lymphocyte signalling.

Neutrophils accumulate around Trichinella spiralis larvae encysted in skeletal muscle cells of the host. The magnitude of the neutrophil infiltration follows a pattern relating to the stage of infection of T.spiralis. This study was performed to determine if there are factors chemotactic for neutrophils present in the sera of mice infected with T.spiralis, and if present, to compare the chemotactic potential of sera from several time points during the infection. Female MRL++ mice hosted the T.spiralis infection and provided neutrophils for all experiments. The chemotactic potentials of sera were tested by placing 150 ul of serum collected at zero, four, 11, or 28 days following initial infection of the mouse with T.spiralis, into the bottom well of a modified Boyden chamber called a deep well chemotaxis chamber. Next a PVP-free polycarbonate micropore membrane with a pore size of 5 um was placed over the bottom well. The top chamber was then fastened to the bottom well and filled with a neutrophil suspension which was obtained by gradient layer centrifugation using the NIM • 2 step gradient reagent system. A cover glass was placed over the opening of the top well and the entire apparatus was incubated at 37°C under 5% C02 in a humidified incubator for four hours. Following the incubation cells which had migrated through to the bottom well were counted using a hemocytometer and the membranes were stained with Diff Quick. The results demonstrate that there are factors present in the sera of mice infected with T.spiralis that elicit the chemotactic response of neutrophils in vivo. This work also demonstrates that sera from mice infected 11 and 28 days are significantly more chemotactic for neutrophils than are sera from uninfected mice and mice infected four days. These findings correlated with the histologic appearance of the infected skeletal muscle at four, 11 and 28 days post infection as determined by other members of our laboratory. The chemokines IL-8 and KC, and other chemotactic factors such as C5a are discussed as potential mediators of the neutrophil chemotaxis found in this experiment.

Tous les êtres vivants présentent un arsenal de défenses contre les pathogènes, et la réponse inflammatoire constitue le processus initial de cette défense, qui s’achève par la réparation des tissus lésés. Paradoxalement, un processus inflammatoire prolongé est également associé à de nombreuses pathologies comme l’athérosclérose, l’asthme, les maladies auto-immunes mais aussi certains cancers. Le recrutement excessif de leucocytes au site de l’inflammation est un processus commun à ces pathologies. Dès lors, la compréhension et la maîtrise du phénomène complexe et finement orchestré de la migration sélective des populations leucocytaires, appelée chimiotactisme, sont des enjeux majeurs de la recherche médicale contemporaine. Les récepteurs aux peptides formylés bactériens et mitochondriaux (FPRs) forment la première famille de récepteurs chimiotactiques identifiée. Elle comprend trois membres, FPR1, 2 et 3, présentant un haut niveau de similitude et partageant certains de leurs multiples ligands. Le troisième membre de ce groupe, FPR3, reste actuellement le moins bien connu. Récemment, un agoniste de FPR3, affin et spécifique, a été identifié dans le laboratoire. Il s’agit du peptide F2L, qui correspond aux 21 premiers acides aminés de la protéine intracellulaire HEBP1. Dans le cadre de ce travail de thèse, nous nous sommes attelé à la caractérisation approfondie du récepteur FPR3 et son ligand peptidique F2L. Dans un premier temps, et à l’aide d’anticorps validés dans le cadre de ce travail, nous avons montré que le peptide F2L induit le chimiotactisme d’un ensemble de populations leucocytaires qui expriment FPR3, dont les sous-populations de macrophages des poumons, du colon et de la peau, les éosinophiles et les cellules dendritiques plasmacytoïdes. Cette distribution suggère, pour FPR3, une fonction dans la réponse inflammatoire. Nous avons pu montrer ensuite que F2L peut être généré par la protéolyse de son précurseur, HEBP1, sous l’action de la cathepsine D des macrophages. La cathepsine D est une aspartique protéase lysosomiale impliquée dans l’homéostasie cellulaire, les processus apoptotiques et inflammatoires physiologiques et pathologiques, et dans le développement tumoral. Il s’agit désormais d’identifier dans quel compartiment et sous quelles conditions F2L est produit et sécrété. Enfin, parallèlement à ces travaux, nous avons démontré que la cathepsine G, une sérine protéase contenue dans les granules azurophiles des neutrophiles, active également le récepteur FPR3. Des résultats préliminaires suggèrent un mode d’activation alternatif du récepteur, impliquant la protéolyse d’un troisième partenaire et la génération d’un agoniste actuellement non identifié. Le couple FPR3-F2L semble dès lors impliqué dans l’induction ou la résolution de la réponse inflammatoire en recrutant les éosinophiles, monocytes, macrophages et cellules dendritiques au site de la lésion.

In this paper, we discuss the local and global existence of week solutions for some hyperbolic-parabolic systems modelling chemotaxis.

Thesis (M.S.)--Brigham Young University. Dept. of Chemistry and Biochemistry, 2008. / Includes bibliographical references (p. 49-53).

Thesis (M. S.. in Biomedical Engineering)--Vanderbilt University, Dec. 2009. / Title from title screen. Includes bibliographical references.

Thesis (Ph. D.)--University of Oregon, 2000. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 113-123). Also available for download via the World Wide Web; free to University of Oregon users.