Copyright ©ERS Journals Ltd 2003 Upregulated response to chemokines in oxidative metabolism of eosinophils in asthma and allergic rhinitisDepts of 1 Clinical and Laboratory Medicine and 2 Oto-Rhino-Laryngology, Akita University School of Medicine, Akita, Japan CORRESPONDENCE: J. Chihara, Dept of Clinical and Laboratory Medicine, Akita University School of Medicine, Hondo, Akita 010-8543, Japan. Fax: 81 188362624. E-mail: chihara@hos.akita-u.ac.jp Keywords: CC chemokine receptor 3, eosinophils, eotaxin, interleukin-5, reactive oxygen species, regulated on activation, normal T-cell expressed and secreted
Received: April 4, 2002
This study was supported by grants-in-aid for Scientific Research from the Ministry of Education and Science, and the Ministry of Health and Welfare (both Tokyo, Japan).
Reactive oxygen species (ROS) from eosinophils are known to cause tissue damage in allergic inflammation. CC chemokines, especially eotaxin and regulated on activation, normal T-cell expressed and secreted (RANTES), are involved not only in chemotaxis but also in eosinophil activation, such as ROS production. It has been shown that eosinophils from allergic patients are not functionally equivalent to those from normal subjects. In the present study, the characteristics of chemokine-primed ROS production in eosinophils from allergic patients and normal controls were compared. After pretreatment with chemokines, eosinophils were stimulated with calcium ionophore A23187 [GenBank] . ROS production by eosinophils was measured using luminol-dependent chemiluminescence. Both RANTES and eotaxin exhibited a priming effect on calcium ionophore-induced ROS production from eosinophils. Despite there being no difference in expression of CC chemokine receptor 3, the priming effect of RANTES and eotaxin was significantly enhanced in eosinophils from the patients. Interleukin-5 further enhanced the priming effect of chemokines in eosinophils from normal subjects, but not those from allergic subjects. The present results suggest an upregulated response to chemokines in eosinophils from allergic patients, and that interleukin-5 can induce a similar phenotype to that found in vivo in allergic patients. One characteristic feature of allergic disease is tissue inflammation, involving the activation of T-lymphocytesand eosinophils 1. The severity of allergic disease is influenced bythe degree of eosinophil activation. During the process ofallergic inflammation, eosinophils migrate into tissues andrelease toxic granule proteins and reactive oxygen species (ROS), leading to tissue damage 2. ROS production is elicited by several stimuli, such as immunoglobulins (Igs) and cytokines 3. It has been previously reported that the signal from adhesion molecules plays a critical role in ROS production by eosinophils 4. TheCC chemokines, especially eotaxin and regulated on activation, normal T-cell expressed and secreted (RANTES), possess a selective chemotactic activity for eosinophils. Besides chemotaxis, these chemokines are involved in eosinophil activation. Indeed, it has been shown recently that chemokines prime ROS production by eosinophils 5, 6. It has been shown that eosinophils from allergic patients are not equivalent in effector function to those from normalsubjects 79. However, the different response of eosinophils to chemokines has not been fully elucidated. Therefore, in thepresent paper, comparative studies were performed inallergic patients and normal subjects regarding the primingeffects of chemokines on ROS production from eosinophils.
Subjects Venous blood was drawn from 12 healthy nonallergic adults (age 1840 yrs, mean 27.3 yrs; four females) and from 15 patients with allergic diseases of the respiratory tract (2332 yrs, mean 25.1 yrs; five females). Age and sex distribution were not significantly different between normal subject and patient groups. All subjects gave informed consent, and the study was carried out according to the principles of the Declaration of Helsinki. None of the subjects had received either any medication for 24 h or steroids for 2 weeks before blood collection. Normal subjects were defined on thebasis of a lack of a clinical history of allergy or other similar diseases. All patients had allergic asthma and/or allergic rhinitis, IgE concentrations of >400 International Units (IU)·mL1 and an IgE radioallergosorbent test result of higher than class 3 against at least one of the common airborne allergens, such as house dust mite, pollens or fungi. The numbers of patients with asthma and allergic rhinitis were seven and 11, respectively (three had both asthma and allergic rhinitis). Asthmatic patients participating in the present study met the American Thoracic Society's definition of asthma. Allpatients with allergic rhinitis showed symptoms at the time of blood collection (nasal congestion, sneezing, rhinorrhoea, itchy eyes, etc.). The eosinophil counts in the peripheral blood of patients were significantly higher than those of normal subjects (683.3±374.0 versus 126.0±80.4 cells·mm3; p<0.01).
Eosinophil isolation
Luminol-dependent chemiluminescence
Flow cytometric analysis of eosinophil surface CC chemokine receptor 3
Measurement of intracellular calcium concentration
Statistical analysis
Luminol-dependent chemiluminescence in eosinophils from normal and allergic subjects ROS production by eosinophils was examined in terms of luminol-dependent chemiluminescence evoked by calcium ionophore A23187 [GenBank] , and compared between normal subjects and allergic patients. ROS production from eosinophils as measured via integral intensity was significantly greater in allergic patients than normal subjects (fig. 1
Effect of eotaxin and regulated on activation, normal T-cell expressed and secreted on reactive oxygen species production by eosinophils from normal and allergic subjects The priming effect of eotaxin and RANTES on ROS production was compared in normal subjects and allergic patients. Figures 2a and b
Effect of CC chemokine receptor 3 antagonist on chemokine-primed reactive oxygen species production by eosinophils In order to confirm the involvement of CCR3 in chemokine-primed ROS production, the effect of a CCR3 antagonist thatinhibits the binding of eotaxin to human eosinophils 11 wasinvestigated. The CCR3 antagonist completely inhibited eotaxin- and RANTES-primed ROS production (fig. 4
CC chemokine receptor 3 expression on eosinophils from normal and allergic subjects In order to investigate the different response of eosinophils from allergic patients, expression of CCR3, a common receptor for RANTES and eotaxin, was determined. The percentage of CCR3-positive cells and mean fluorescent intensity compared to controls were used as parameters of receptor expression. No significant differences in either were observed between eosinophils from allergic and normal subjects (fig. 5
Effect of interleukin-5 on chemokine-primed reactive oxygen species production by eosinophils IL-5 has been shown to enhance the effector function of eosinophils 12, 13. IL-5 augments eosinophil responses to platelet-activating factor, formyl-methionyl-leucyl-phenylalanine, platelet factor-4 and complement factor 5a 13, 14. Therefore, the possible involvement of IL-5 in the different eosinophil responses to chemokines between normal subjectsand patients was examined. In a preliminary study, a 1-ng·mL1 dose of IL-5, as indicated in previous reports of serum concentrations in allergic patients 15, had no effect onROS production by eosinophils in the absence of chemokines (fig. 6a
In addition, GM-CSF (1 ng·mL1) did not affect the priming effect of eotaxin or RANTES (125.5±17.6 versus 119.7±9.4% control integral chemiluminescent intensity, eotaxin alone versus eotaxin plus GM-CSF). Moreover, the CCR3 expression of eosinophils did not change after treatment with IL-5 (fig. 7
In order to investigate whether blockade of IL-5R on allergic eosinophils is able to reverse this augmentative effect on chemokine priming, allergic eosinophils were preincubated with the anti-IL-5R antibody prior to eotaxin stimulation. Blockade of the IL-5 receptor did not affect the priming effect of eotaxin in allergic eosinophils (156.6±10.2 versus 159.6±18.8% control integral chemiluminescent intensity, eotaxin alone versus eotaxin plus anti-IL-5R ; n=4).
Effect of interleukin-5 on chemokine-induced calcium influx in eosinophils
Several studies have reported that eosinophil function is highly dependent on the pathophysiological conditions of allergic disease 7, 1619. The present study shows upregulated oxidative metabolism in eosinophils obtained from allergic patients compared to those from normal subjects. Asimilar increase in ROS production by eosinophils was observed in allergic patients 16, 17. It has also been demonstrated that eosinophils from subjects undergoing allergen challenge or patients with such symptoms exhibit enhanced ROS production 18, 19. Taking the results of these studies together with the present observations, eosinophils from allergic patients may have already been activated in the peripheral blood stream before they infiltrate the tissues. Moreover, in the present study, functional upregulation of the response to chemokines in ROS production by eosinophils obtained from allergic patients was observed. The priming effect of both RANTES and eotaxin on ROS production was significantly greater than that on eosinophils from normal subjects. Even at the suboptimal dose for eosinophils from normal subjects, eosinophils from allergic patients showed enhanced ROS production after treatment with chemokines. These results suggest that eosinophils from allergic patients are more sensitive and responsive to chemokines.
It has been reported that eotaxin and IL-5 cooperate to regulate eosinophil trafficking during allergic inflammation 20, 21. Schweizer et al. 22 reported that chemokine-induced responses are very sensitive to priming by cytokines such as IL-5. Therefore, in order to extend understanding of these upregulated sensitivities and their responsiveness to chemokines, the possible involvement of cytokines, such as IL-5 and GM-CSF, in the priming effect of chemokines was examined. It was demonstrated that a low concentration (1 ng·mL1) of IL-5 enhanced chemokine-primed ROS production by eosinophils, suggesting that IL-5 may enhance the responsiveness to chemokines. Although a similar tendency has been observed in other eosinophil functions, such as degranulation and migration 14, 22, 23, this is the first report of a priming effect of IL-5 on chemokine-primed ROS production from eosinophils. Interestingly, no augmentative effect of GM-CSF was demonstrated despite the ß subunit (ßc) being common to both IL-5 and GM-CSF receptors. Although ßc plays a major role in IL-5 signalling 24, recent evidence indicates that the specific IL-5 receptor IL-5R It has been reported that IL-5 is produced by eosinophils themselves, especially in allergic conditions 27. One possibility is that allergic eosinophils can be primed by IL-5 produced by themselves. However, it was demonstrated thatblockade of the IL-5 receptor on allergic eosinophils could not reverse the priming effect of chemokines. This resultindicates that the upregulated response to chemokines observed in allergic eosinophils was not elicited by IL-5 produced after eosinophil isolation. Moreover, the augmentative effect of IL-5 was observed only in eosinophils from normal subjects and not in those from allergic patients. This distinct phenotype is in line with data demonstrating in vivo priming of adhesion-associated responses of peripheral blood eosinophils of patients with allergic diseases 13, 14. Therefore, eosinophils from allergic patients may undergo IL-5 exposure in the blood stream, resulting in great enhancement of responsiveness to chemokines, as demonstrated in the present study. The possibility of differences in expression of CCR3 as a means of explaining the different responses to chemokines was examined, but no significant difference was found in CCR3 expression between patients and normal subjects. Furthermore, CCR3 expression of eosinophils did not change after treatment with IL-5. These observations suggest that functional upregulation of response through CCR3 in allergic patients does not depend on an increase in CCR3 expression. As regards signalling of eosinophils, it was examined whether IL-5 modulates the calcium mobilisation induced by chemokines. However, IL-5 did not affect the intracellular calcium influx induced by eotaxin. It has recently been reported that the baseline activity of phosphatidylinositol 3-kinase is elevated in allergic patients compared to normal subjects, together with involvement of IL-5 in phosphatidylinositol 3-kinase activation 28, 29. Thus, it may be assumed that IL-5 modulates the downstream signalling of CCR3 to enhance the response to eotaxin. Beside the involvement of cytokines, such as IL-5, in the upregulated response of eosinophils from allergic patients to chemokines, it can be presumed that other mechanisms, such as CCR3 polymorphism 30 and change in affinity/avidity, are involved. Recently, CCR3 has become a target in the treatment of allergic diseases such as asthma, atopic dermatitis and allergic rhinitis. Indeed, an inhibitory effect of CCR3 antagonist on chemokine-mediated eosinophil function has been found (manuscript in preparation). In conclusion, the present study has demonstrated an enhanced response to chemokines in the reactive oxygen species production of eosinophils from allergic patients, with the possible involvement of interleukin-5 in that enhancement, and without changes in CC chemokine receptor 3 expression. Further studies are required to elucidate the mechanisms of the different responses of CC chemokine receptor 3.
The authors would like to thank Y. Kamada, T. Takahashi and H. Oyamada fortheir help and support.
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