Ricardo E. Duque

Inhibition of neutrophil activation by p-bromophenacyl bromide and its effects on phospholipase A2

1 In an effort to elucidate the nature of the inhibitory effects of p‐bromophenacyl bromide (pBPB) on neutrophil stimulation, we have examined its effects on several stages of stimulus‐response coupling. 2 Pretreatment of rat neutrophils with pBPB resulted in a dose‐ and time‐dependent irreversible inhibition of both N‐formylmethionyl‐leucylphenylalanine (fMet‐Leu‐Phe)‐induced lysosomal enzyme release and change in transmembrane potential. 3 Inhibition of the biological responses to the chemotactic peptide f Met‐Leu‐Phe was not due to receptor inactivation since f Met‐Leu‐[3H]‐Phe binding to the formyl peptide receptor was not significantly altered by pBPB pretreatment. 4 Inhibition by pBPB of phorbol myristate acetate (PMA)‐induced changes in transmembrane potential and the generation of superoxide (0–2) was also observed. 5 pBPB treatment appeared to inhibit activation of the NADPH oxidase without a direct effect on the oxidase itself. 6 This inhibitory effect was not accompanied by cell death or decrease in cellular titratable sulphydryl groups (at least at doses < 20 μM). 7 There was, however, significant inhibition of a membranous fraction of f Met‐Leu‐Phe‐induced phospholipase A2 activity by pretreatment with 10 μM pBPB, although total cellular phospholipase A2 was only minimally (< 20% inhibition) affected. 8 These data would indicate that pBPB inhibits an early event associated with stimulus‐response coupling in rat polymorphonuclear leukocytes (i.e. change in transmembrane potential). The inhibitory effects of pBPB may be secondary to the inhibition of a critical membranous fraction of cell bound phospholipase A2 activity or its activation, necessary for the initiation of cell activation.

The macrophage adherence phenomenon: Its relationship to prostaglandin E2 and superoxide anion production and changes in transmembrane potential

Mononuclear phagocytes are undoubtedly the sine qua non of chronic inflammatory reactions. This is demonstrated by their unique ability to function as phagocytic, secretory, or effector cells during the course of an immune event. Although macrophages can perform a variety of immune tasks, their ability to function appropriately is dependent upon the mode of elicitation, the stimulus under investigation, the source of the macrophages (peritoneal, alveolar, etc.), and whether the macrophages are monolayers or in suspension. We have examined the relationship between adherent and non-adherent elicited peritoneal macrophages in terms of prostaglandin E2 (PGE2) and superoxide anion (O2-) production; in addition, we have studied these elicited macrophages in suspension for their ability to undergo transmembrane potential changes in response to several stimuli. Non-adherent, elicited peritoneal macrophages demonstrated an increase in basal PGE2 production, and were refractory to particulate stimulus. After monolayer formation, basal PGE2 levels dropped and the cells could respond to both soluble and particulate stimuli. Only adherent macrophages could respond to a specific challenge and synthesize O2-. Both O2- production and depolarization of the transmembrane potential were suppressed in cells in suspension. Furthermore, both exogenous PGE2 and supernatant from macrophages in suspension could modulate O2- production by PMA challenged macrophages monolayers. These studies indicate that PGE2 may modulate macrophage function and dictate activity as macrophages go from the non-adherent to adherent state.

Site-dependent phenotypic heterogeneity in peripheral T-cell lymphoma

Peripheral T-cell lymphomas constitute a heterogeneous population of postthymic T-cell malignancies. Characteristically, they present a varied phenotypic expression, which can be helpful in establishing the diagnosis. A case of a peripheral T-cell lymphoma in a 76-year-old man is described. The malignant cells in the skin and bone marrow were of the T4 (helper/inducer) phenotype, yet they did not express pan-T-cell antigens, such as T11, or functional E rosettes. In a biopsy specimen from a lymph node, however, the malignant cells had a helper/inducer phenotype and also expressed the pan-T-cell antigens T11 and Leu-5. Additionally, the malignant cells from the lymph node formed E rosettes. This study demonstrates the phenotypic heterogeneity of malignant T cells, which appears to be site-dependent.

PROSTAGLANDIN MODULATION OF N-FORMYLMETHIONYLLEUCYLPHENYLALANINE- INDUCED TRANSMEMBRANE POTENTIAL CHANGES IN RAT NEUTROPHILS

Prostaglandins of the E-series (PGEs) and PGI2 will inhibit formylmethionylleucylphenylalanine-(f-Met-Leu-Phe) induced lysosomal enzyme release and superoxide-anion (O2-) production by neutrophils. The inhibitory effects of PGEs and PGI2 on neutrophil functional responses have been correlated with their ability to increase intracellular cAMP. In this study we have examined the effects of PGEs and PGI2 on f-Met-Leu-Phe- and phorbol-myristate-acetate-induced rat neutrophil membrane potential changes using an optical probe of membrane potential 3,3-dipropylthiodicarbocyanine iodide. 15-(S)-15-methyl-PGE1 (15-methyl-PGE1), a stable analogue of PGE1 and PGI2 inhibited f-Met-Leu-Phe-induced transmembrane potential changes in a dose-dependent manner. This inhibition was correlated with the ability of these agents to increase intracellular cAMP levels and inhibit O2- production and degranulation. In contrast, 15-methyl-PGE1 and PGI2, did not inhibit phorbol-myristate-acetate-induced transmembrane potential changes and O2- production. These results suggest independent mechanisms of activation of neutrophils by phorbol myristate acetate and f-Met-Leu-Phe, and they also suggest that the inhibitory effects of prostaglandins and cAMP on f-Met-Leu-Phe-stimulated cells is at a step or steps prior to activation of those processes involved in effecting changes in transmembrane potential, which are common to both stimuli.