Mandell, Gerald L.
Biology of phagocytic cells withemphasis on neutrophils and microbial interactions.
In order to better understand the normal and abnormal function of phagocytes, Mandell is examining the interrelationships of membrane perturbation, receptor topographic changes, membrane cytosolic calcium concentrations and correlating these with effector functions. Calcium is a prime candidate as a second messenger in relating surface stimuli to activities of the cell. Mandell's laboratory reported a marked increase in the leading edge of migrating cells and in PMN periphagosomal calcium following phagocytosis. This regional increase appears to be closely related to the activation of neutrophil oxidases and to degranulation. Neutrophils ingesting particles that do not trigger degranulation or oxidative activity do not result in increases in periphagosomal calcium concentration.
Calcium is measured in Mandell's laboratory by visualizing fluorescence emitted from calcium dependent probes such as Fura 2 utilizing a computer-based image enhancement and analysis microscopic system. He is able to accurately and reproducibly measure intracellular calcium concentration in single living human neutrophils. Changes in calcium concentrations during neutrophil activation by either particulate or soluble stimuli can be determined as can be the effect of various inhibitors and promoters of phagocyte effector functions.
Cytokines such as TNF and IL-1 activate neutrophils in part by up-regulating MAC-1 expression. Certain alkylxanthines and adenosine agonists are able to counteract cytokine effects on neutrophils. We are presently evaluating the effects of alkylxanthines and adenosine on phagocyte morphology, and expression of adherence factors on the leukocyte surface (integrins and selectins). We are studying modulation of macrophage/giant cell maturation by purines including adenosine receptor antagonists and are preparing to study the effect of adenosine on the expression of adherence factors on leukocytes.
Because of the common problem of diarrhea from Clostridium difficile infection in patients receiving wide spectrum antibiotics, our laboratory hasrecently begun studying the role of the observed neutrophil infiltration into the intestine in this disease. Specifically, we have found profound effects of Clostridium difficile toxin A on neutrophil morphology and function including inhibition of PMN migration, and enhancement of adherence, and the expression of MAC-1 on the neutrophil surface. We are now involved with examining the mechanisms for these neutrophil actions, and in collaboration with Drs. Richard Guerrant and David Bobak the consequences of altered neutrophil function in this disease.