MECHANISM OF HUMAN LEUKOCYTE CHEMOTAXIS

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Our general objective is to understand mechanisms of control of human neutrophil and monocyte chemotactic function as a component of leukocyte recruitment to sites of inflammation/infection. It applies to two long range goals to know how recruitment of leukocytic phagocytes is normally controlled, and to identify therapy to prevent loss of phagocyte chemotactic function associated with injury, sepsis, or cytokine immunotherapy. Our experimental approach is to identify acquired defects in patient leukocyte chemotaxis and reproduce these defects by various in vitro treatments of control neutrophils to identify inhibitory agents and mechanisms of inhibition. Our working model of mechanisms of leukocyte chemotactic dysfunction in vivo involves altered (i) expression/function of receptors for multiple attractants, (ii) expression of receptors mediating attachment to vascular endothelium, and (iii) components of the cytoskeleton required for motility. Specific aims are based upon our "breakthrough" observation that tumor necrosis factor-alpha (TNF) is a "natural" inhibitor of neutrophil chemotactic sensitivities to multiple attractants. We will apply this observation to studies to identify TNF as the neutrophil chemotaxis inhibitor in patients with thermal injury and patients receiving cytokine immunotherapy (IL-2) for cancer: Aims 1 and 4. Additional experiments will be done to establish the mechanism of TNF-mediated down- regulation of receptors for C5a and IL-8: Aim 2, and the unique ability of TNF to control leukocyte chemotaxis through receptor modulation: Aim 3. Our studies of IL-2 immunotherapy patients are NEW to this proposal and are based upon evidence published by two laboratories during April/May of 1990 that IL-2 infusion produces a neutrophil chemotactic defect associated with significant infectious complications experienced by these patients. Our ability to establish the role of TNF as an inhibitor of leukocyte chemotaxis is based upon a set of criteria describing a "TNF phenotype" derived from studies of control neutrophils treated with TNF in vitro. Measurements of chemoattractant receptors will involve use of fluorescent analogs of FMLP, C5a, and IL-8 and flow cytometry. Eliminating the accumulation or activity of TNF would benefit thermal injury, trauma, and septic patients, as well as patients receiving cytokine immunotherapy. A reagent mimicking this activity of TNF would also be useful therapeutically to limit toxic accumulation of neutrophils in rheumatic, inflammatory bowel, and dermatological diseases and myocardial infarction.