Activation and release of enzymes and major basic protein from guinea pig eosinophil granulocytes induced by different inflammatory stimuli and other substances. A histochemical, biochemical, and electron microscopic study

Mast cell tryptase activates peripheral blood eosinophils to release granule-associated enzymes

BACKGROUND

Mast cells and eosinophils are important effector cells in asthma. Understanding their interactions is essential for studying asthma pathophysiology. Inflammatory mediators released from mast cells, such as arachidonic acid metabolites, TNF and IL-5, are important in eosinophil biology. However, little is known about the effects of mast cell-specific mediators, such as tryptase, on eosinophils. Our objective was to investigate the effects of mast cell tryptase on human peripheral blood eosinophils.

METHODS

Peripheral blood eosinophils isolated from asthmatic individuals were activated using various concentrations of tryptase- and protease-activated receptor-2 (PAR-2)-activating peptides (PAR-2 AP). Eosinophil activation was evaluated by the release of granule mediators, superoxide release, estimation of eosinophil survival, changes in intracellular Ca2+ concentration and mitogen-activated protein kinase activation.

RESULTS

Tryptase induced the release of eosinophil peroxidase and beta-hexosaminidase from peripheral blood eosinophils but had no effect on RANTES release. Eosinophils isolated from two thirds of our donors responded to tryptase, while the remainder appeared not to respond. Release of granule mediators was dependent on tryptase enzymatic activity. To identify the mechanism of eosinophil activation by tryptase, we studied the expression of PAR-2 by eosinophils and its function. Using RT-PCR, we amplified PAR-2 from eosinophils. However, flow cytometry failed to detect significant PAR-2 expression on the surface of eosinophils. The PAR-2 AP SLIGRL-NH2 did not induce eosinophil activation by any of the methods we employed.

CONCLUSION

Our data indicate that mast cell tryptase may affect eosinophil activation status independently of PAR-2.

Desensitization of beta2-adrenoceptor and hypersensitization to phosphodiesterase inhibitors elicited by beta2-agonists in guinea pig eosinophils

BACKGROUND

Although the existence of functional beta(2)-adrenoceptor on eosinophils has been reported, the effects of desensitization of beta(2)-adrenoceptors on eosinophils have not been well documented.

OBJECTIVE

The effects of desensitization of beta(2)-adrenoceptors on the degranulation of guinea pig eosinophils were investigated.

METHODS

Guinea pig eosinophils were stimulated with the calcium ionophore A23187, and eosinophil peroxidase (EPO) release was determined. Changes in intracellular cyclic adenosine monophosphate (cAMP) levels were also measured.

RESULTS

A23187-induced EPO release from guinea pig eosinophils was inhibited in a concentration-dependent manner by pretreatment for 5 minutes with fenoterol, clenbuterol, and salbutamol. Such effects of beta(2)-agonists were abolished by pretreatment with KT5720, an inhibitor of protein kinase A. Desensitization of the inhibitory effects of beta(2)-agonists was observed when the incubation time was prolonged. Fenoterol (10(-6) mol/L) induced almost complete desensitization after 120 minutes of incubation, whereas clenbuterol did not bring about significant desensitization. The inhibitory effects of fenoterol and clenbuterol on A23187-induced EPO release were correlated with increases in the intracellular cAMP levels evoked by either compound. After incubation of eosinophils with 10(-6) mol/L fenoterol for 120 minutes to induce complete desensitization of beta(2)-adrenoceptors, the inhibitory effects of theophylline and rolipram were increased by about 100-fold in the desensitized cells, although the effects of forskolin and dibutyryl cAMP were not affected by beta(2)-adrenoceptor desensitization.

CONCLUSIONS

Prolonged incubation with beta(2)-agonists induced desensitization of beta(2)-adrenoceptors. Also, we postulated that hypersensitization of phosphodiesterase to its inhibitors occurs in beta(2)-adrenoceptor-desensitized guinea pig eosinophils.

Effects of CS-518, a thromboxane synthase inhibitor, on eosinophil function

The effects of CS-518 (sodium 2-(1-imidazolylmethyl)-4,5-dihydrobenzo[b]thiophene-6-carboxylate) , a thromboxane A2 synthase inhibitor, on eosinophil accumulation and activation were investigated in an experimental asthmatic guinea pig model and several cellular models. In the in vivo studies, CS-518 inhibited the biphasic eosinophil accumulation in the bronchoalveolar lavage fluid, potently in the early phase, but less potently in the delayed phase. On the other hand, even at the lower dose, CS-518 completely inhibited the hypodensity of eosinophils in the delayed phase. In the in vitro studies, CS-518 suppressed thromboxane A2 production and potentiated prostaglandin I2 production from guinea pig eosinophils. Moreover, CS-518 and prostaglandin I2 suppressed chemotaxis, peroxidase release and superoxide generation in guinea pig eosinophils. In addition, the present studies provide further support for the possibility that thromboxane A2 and prostaglandin I2, which are produced in bronchoalveolar tissue and within eosinophils, are involved in modulation of eosinophil function and suggest that CS-518 is a potent inhibitor of eosinophil activation.

Platelet-activating factor stimulates a rapid accumulation of inositol (1,4,5)trisphosphate in guinea pig eosinophils: relationship to calcium mobilization and degranulation

The effect of platelet-activating factor (PAF) on inositol (1,4,5)trisphosphate (Ins[1,4,5]P3) mass, calcium mobilization, and the release of granule enzymes was studied on guinea pig peritoneal eosinophils (EOSs). PAF evoked a concentration-dependent accumulation of Ins(1,4,5)P3 with a drug concentration that elicits 50% of the maximum attainable response (EC50) of 10 nmol/L; the production of this second messenger was maximal at 1 mumol/L of PAF. Kinetic analysis of PAF (1 mumol/L)-induced Ins(1,4,5)P3 accumulation demonstrated it to be transient with a 3.8-fold increase over resting levels observed at 5 seconds. Thereafter, the level of Ins(1,4,5)P3 declined, returning to vehicle-treated levels 60 seconds after PAF challenge. Lyso-PAF, the inactive precursor and metabolite of PAF, was inactive at all concentrations examined. PAF also induced a rapid, concentration-dependent (EC50, 12 nmol/L) rise in the cytosolic-free calcium concentration ([Ca++]i) in fura 2-AM-loaded EOSs that was transient, peaking after the maximum increase in Ins(1,4,5)P3 mass was observed. A highly significant positive correlation was found between the peak increase in Ins(1,4,5)P3 and the peak rise in [Ca++]i. Functionally, PAF evoked a concentration-dependent release of granule constituents from both the small (arylsulfatase B; EC50, 3 nmol/L) and specific (EOS peroxidase; EC50, 2.7 nmol/L) granules that lagged, temporally, behind both Ins(1,4,5)P3 accumulation and the rise in [Ca++]i. Both the biochemical and functional effects of PAF examined in this study were antagonized by WEB 2086 (300 nmol/L), a selective PAF receptor-blocking drug. It is concluded that stimulus (PAF)-response coupling in guinea pig peritoneal EOSs may involve the receptor-mediated formation of Ins(1,4,5)P3 and subsequent release of intracellularly stored Ca++. This sequence of events may link PAF receptor activation to Ca(++)-dependent cellular responses, such as degranulation.

Eosinophilic granuloma of the bone in Hand-Schüller-Christian disease: extensive in vivo eosinophil degranulation and subsequent binding of released eosinophil peroxidase (EPO) to other inflammatory cells

The eosinophils from bone granuloma, bone marrow, and peripheral blood of a patient with Hand-Schüller-Christian disease (HSCD) were studied by electron microscopy and cytochemistry. Impressive eosinophil degranulation was observed. Extracellular release of eosinophil peroxidase (EPO) and EPO binding to surrounding cells were seen in the granuloma and bone marrow. Cells with peroxidase-positive plasma membrane were also observed in peripheral blood. The pattern of eosinophil degranulation showed quite different features from those described so far. In the granuloma, the process begins with intracytoplasmic release of the granule matrix content, as revealed by both extensive extragranular accumulation of EPO and progressive decrease of the matrix electron density. Core dissolution follows thereafter, leading to complete disappearance of the granules. At the end of the process, the cells show rupture of the plasma membrane and release of their content into the surrounding environment. This pattern of secretion was also observed in blood and marrow eosinophils of the patient. In view of the previously reported findings that EPO binding to inflammatory cells influences their functions, EPO release and binding to surrounding cells in HSCD may play a role in the evolution of the inflammatory lesion in the disease.