P. Daniel Lew

Invasive aspergillosis. Clinical features of 35 proven cases at a single institution.

Thirty-five patients with clinical features and histologically or microbiologically proven infection met predetermined stringent criteria for invasive aspergillosis over a 5-year period at our institution. Underlying conditions included hematologic malignancy, solid tumor, bone marrow and solid organ transplantation, and immunosuppressive therapy. The majority of patients (94%) presented with respiratory symptoms and abnormal pulmonary chest radiography; only 40% had neutropenia at time of infection. Invasive aspergillosis was suspected in only 21 cases (60%). Concomitant infections were present in 83% of patients. Half of patients had pathogenic or potentially pathogenic microorganisms other than Aspergillus spp. isolated from pulmonary specimens at time of aspergillosis. Aspergillus spp. were recovered from sputum in 75% of patients and from bronchoalveolar lavage in only 52%. Invasive aspergillosis is an unexpectedly unrecognized disease with poor outcome; overall mortality was 94% in our series. The lack of sensitivity of diagnostic procedures, together with the high frequency of concomitant infections, delays the time of diagnosis. Early diagnostic tests are needed, and presumptive antifungal therapy among high-risk patients is mandatory.

Effect of leukotriene B4, prostaglandin E2 and arachidonic acid on cytosolic‐free calcium in human neutrophils

Changes in cytosolic free calcium [Ca2+]i and release of beta‐glucuronidase in response to leukotriene B4 (LTB4) were measured in intact neutrophils loaded with the fluorescent Ca2+ indicator, quin 2. LTB4 (10−10 M or higher) caused a rapid rise in [Ca2+]i due to influx from the extracellular medium and release from intracellular pools as well as enzyme release. PGE2 (3 μM) did not alter [Ca2+]i whereas arachidonic acid (10 μM) raised [Ca2+]i. Pretreatment of cells with the chemotactic peptide FMLP inhibited the subsequent rise of [Ca2+]i induced by LTB4. Since chemotactic peptides activate the lipoxygenase pathway of arachidonic acid metabolism, it may be speculated that endogenous LTB4 generation is involved in neutrophil activation.

Effect of serotonin on cytosolic free calcium in adrenal glomerulosa and vascular smooth muscle cells

In view of its vasoconstricting action and of its stimulating effect on aldosterone biosynthesis, serotonin (5-hydroxytryptamine, 5-HT) could play a role in the genesis and/or maintenance of hypertension. The effects are mediated by different specific receptors whose transmembrane signaling system is not elucidated. We have used the fluorescent probe quin 2 to study the effect of 5-HT on cytosolic free calcium in enzymatically dispersed bovine adrenal glomerulosa cells and in cultured rat aortic smooth muscle cells. We also examined the effect of 5-HT on prostacyclin production by rat aortic smooth muscle cells. Serotonin did not modify the level of cytosolic free calcium in adrenal glomerulosa cells. In contrast, serotonin induced rapid, concentration-dependent (10(-8) -10(-5) M) rises of cytosolic free calcium in monolayers of cultured rat aortic smooth muscle cells, from a basal level of 153 +/- 27 nM to peak levels of about 400 nM. Ketanserin (10(-6) M), a specific 5-HT2-receptor antagonist completely blocked the free calcium rise induced by 5-HT. 5-HT induced a concentration-dependent increase in 6-keto-PGF1 alpha production in smooth muscle cells, which was suppressed by ketanserin, indomethacin or removal of calcium from the incubation medium. In contrast nifedipine (10(-6) M) did not modify the response to 5-HT while it abolished the response to vasopressin and did not modify the response to angiotensin II. We conclude that the 5-HT receptors of adrenal glomerulosa cells and vascular smooth muscle cells are linked to two distinct signalling systems which mediate the different biological responses.

Chapter 8 Cytoplasmic Calcium in Phagocyte Activation

Publisher Summary The calcium ion has an unusual importance in biological phenomena. Changes in the cytosolic free calcium concentration [Ca 2+ ] i have evolved as a key intracellular messenger system to couple external stimuli to a variety of complex cellular responses. In phagocytic cells, (i.e., neutrophils and macrophages) changes in [Ca 2+ ] i follow stimulation of several receptors and are thought to be involved in the regulation of adherence, chemotaxis, phagocytosis, degranulation, and production of toxic oxygen metabolites. The challenge for future research in phagocyte physiology will be the discrimination of those responses that are [Ca 2+ ] i -activated and [Ca 2+ ] i -dependent from those simply associated with a change in [Ca 2+ ] i , the latter being due to the ligation of multifunctional receptors generating multiple signals and reactions. With the help of the new Ca 2+ chelators, which allow the manipulation of [Ca 2+ ] i in intact cells, answers to these questions are already becoming available. Yet nothing is known of the “missing messengers” that mediate phagocyte responses in those instances in which no generation of known intracellular signals has been documented.

Role of Plasma Membrane Potential in Granulocyte Activation

Plasma membrane potential changes associated with ligand-receptor interaction have been demonstrated in both excitable and non-excitable cells. Among the latter, hyperpolarization and/or depolarization have been described for lymphocytes,’S2 platelets,’ and granulocyte^^^^ In excitable tissues such as neurons, neuroendocrine and muscle cells, the physiological role for plasma membrane depolarization has been well characterized. These cells possess plasma membrane ion channels that are sensitive to, or gated by, membrane p~tential.~.’ On the other hand, the role of plasma membrane potential changes in non-excitable cells remains mysterious. In neutrophils, plasma membrane depolarization is elicited by a number of particulate and soluble agonists (e.g., formyl-methionyl oligo peptides that bind to specific cell surface receptors coupled to Ca2+ mobilization and phosphoinositide breakdown). The aim of our study was to examine the relationship between plasma membrane potential changes and [Ca2+Ii n response to fMet-Leu-Phe in human neutrophils and in the human promyelocytic leukemia cell line HL60, after differentiation with dimethylsulfoxide (DMSO). Our results indicate that: ( 1 ) Chemotactic peptide-dependent plasma membrane depolarization is a post-receptor event and probably depends on protein kinase C activation. In fact, receptor-activated depolarization occurred both at high and resting [Ca2+],, but was inhibited at very low [Ca2+Ii. On the contrary, phorbol myristate acetate (PMA)-induced plasma membrane depolarization was independent of [Ca2+Ii. Threshold Met-Leu-Phe concentrations for plasma membrane depolarization (lo-’ M) was at least one log unit higher as compared to [Ca”], increases ( 5 x lO-’OM) and coincident with the increase of NADPH-oxidase activation. Nearly maximal [Ca”], increases were elicited by 3 x M met-Leu-Phe in the absence of any significant plasma membrane potential change.