Dissociation by steroids of eosinophilic inflammation from airway hyperresponsiveness in murine airways
© The Author(s) 2003
Received: 25 January 2002
Accepted: 21 November 2002
Published: 21 March 2003
The link between eosinophils and the development of airway hyperresponsiveness (AHR) in asthma is still controversial. This question was assessed in a murine model of asthma in which we performed a dose ranging study to establish whether the dose of steroid needed to inhibit the eosinophil infiltration correlated with that needed to block AHR.
The sensitised BALB/c mice were dosed with vehicle or dexamethasone (0.01–3 mg/kg) 2 hours before and 6 hours after each challenge (once daily for 6 days) and 2 hours before AHR determination by whole-body plethysmography. At 30 minutes after the AHR to aerosolised methacholine the mice were lavaged and differential white cell counts were determined. Challenging with antigen caused a significant increase in eosinophils in the bronchoalveolar lavage (BAL) fluid and lung tissue, and increased AHR.
Dexamethasone reduced BAL and lung tissue eosinophilia (ED50 values of 0.06 and 0.08 mg/kg, respectively), whereas a higher dose was needed to block AHR (ED50 of 0.32 mg/kg at 3 mg/ml methacholine. Dissociation was observed between the dose of steroid needed to affect AHR in comparison with eosinophilia and suggests that AHR is not a direct consequence of eosinophilia.
This novel pharmacological approach has revealed a clear dissociation between eosinophilia and AHR by using steroids that are the mainstay of asthma therapy. These data suggest that eosinophilia is not associated with AHR and questions the rationale that many pharmaceutical companies are adopting in developing low-molecular-mass compounds that target eosinophil activation/recruitment for the treatment of asthma.
Keywordsairway hyperresponsiveness eosinophilia steroids
Airway inflammation and hyperresponsiveness (AHR) are recognised as major characteristics of bronchial asthma; however, their relationship is still poorly understood. Exposure to allergen causes an increase in airway responsiveness that is associated with an influx of inflammatory cells, particularly eosinophils, into the airways in allergic humans  and sensitised mice , which suggests a causal relationship between airway inflammation and AHR [3, 4]. However, there is also much published literature suggesting that there is no relationship between allergic airway inflammation and AHR.
In this study we wished to determine whether there was a dissociation between the effective dose of a steroid, dexamethasone, needed to affect antigen-induced AHR in comparison with that needed to affect airway inflammation in the mouse. We have previously described a murine model of asthma that includes non-specific AHR and associated eosinophilia in the airways . In the present study we followed the same sensitising and challenging protocol but decided to determine AHR in conscious, spontaneously breathing, unrestrained mice by whole-body plethysmography [6–9]. Airway responsiveness was expressed as enhanced pause (P enh), a calculated value, which is an indirect measurement that is correlated with measurement of airway resistance, impedance and intrapleural pressure in the same animal . This method was chosen instead of our previously used invasive method because it might offer several potential advantages: it is technically less demanding, it allows repeated measurements over a long period and it avoids the use of anaesthetic and mechanical ventilation. However, one possible disadvantage is that one cannot rule out a contribution by the nose and upper respiratory tract to the parameters measured. This method of antigen-induced airway inflammation and AHR is very similar to that of Dohi et al.  in which they report a strong correlation between P enh and eosinophil number in bronchoalveolar lavage (BAL) fluid.
Materials and methods
Male Balb/C mice (14–16 g, 5 weeks old), were obtained from Harlan (Bicester, Oxon., UK), and housed for 1 week before experiments were initiated. Food and water were supplied ad libitum. Experiments were performed in accordance with the UK Home Office guidelines for animal welfare based on the Animals (Scientific Procedures) Act 1986.
The aim of this study was to determine whether there was dissociation between the effective dose of a steroid needed to affect antigen-induced airway inflammation and AHR.
Sensitisation and antigen challenge protocol
Mice were immunised on days 0 and 14 by intraperitoneal (i.p.) injection of 10 μg of ovalbumin (Grade V; Sigma-Aldrich, Poole, Dorset, UK), in 0.2 ml of saline (Fresenius Kabi, Warrington, Cheshire, UK) with 20 mg of aluminium hydroxide (Merck, Lutterworth, Leicester, UK). From day 21 the animals were challenged with aerosolised ovalbumin (5% in saline) or vehicle (saline) for 20 minutes per day on six consecutive days. Aerosol generation was achieved by use of an air-driven nebuliser (System 22; Medic-aid, Pagham, West Sussex, UK).
Administration of dexamethasone
Vehicle (1% carboxymethylcellulose [Merck, Lutterworth, Leics., UK] in distilled water) or dexamethasone (Sigma-Aldrich) was administered twice daily by the oral route in a dose volume of 10 ml/kg (0.01–3 mg/kg), the day before the first ovalbumin challenge, 2 hours before and 6 hours after subsequent challenges and on the morning of the AHR determination.
Airways mechanics measurements in nonrestrained, conscious mice
Twenty-four hours after the last ovalbumin challenge, mice were placed in a whole-body plethysmograph to facilitate the measurement of lung function as described by Tsuyuki et al. . Bronchoconstriction to aerosolised methacholine (MCh) (3 or 10 mg/ml for 60 seconds with 5 minute intervals) (Sigma-Aldrich) was determined.
Inflammatory cells in the lung
One hour after the last MCh challenge the mice were killed by anaesthetic overdose (pentobarbitone sodium, 200 mg/kg; Rhone Merieux, Harlow, Essex, UK). BAL was performed with three 0.3 ml aliquots of Roswell Park Memorial Institute medium (RPMI 1640; Life Technologies, Paisley, Renfrewshire, UK). The lungs were removed, and were then cleaned and finely chopped after blood had been perfused out. The chopped tissue was then digested enzymatically to obtain inflammatory cells, as described by Underwood et al. . Total counts of cells recovered in the BAL fluid and tissue digest were made with an automated cell counter (Sysmex F-820; Sysmex UK, Linford Wood, Bucks., UK). Differential counts of cells (eosinophils, neutrophils, macrophages, monocytes and lymphocytes) recovered in the samples were made by light microscopy, of cytocentrifuge preparations (100 μl aliquots spun at 700 rpm for 5 minutes at low acceleration) (Cytospin; Shandon Scientific, Runcorn, Cheshire, UK), which had been stained with Wright-Giemsa stain (Sigma-Aldrich), with a Hematek 2000 (Ames Co., Elkhart, Indiana, USA).
All values are presented as means ± SEM per group with n = 10. ED50 values stated are defined as the amount of drug required to elicit 50% of the maximum inhibition. Statistical analysis was made by analysis of variance with a correction for multiple comparisons. P < 0.05 was considered to be statistically significant.
Inflammatory cells in the lung
Effect of dexamethasone treatment on inflammatory cell numbers in bronchoalveolar lavage (BAL) fluid and lung tissue after the last antigen challenge in sensitised mice
MCh challenge (3 mg/ml)
AHR peak changes, ED50
AHR AUC changes, ED50
Effect of dexamethasone treatment on inflammatory cell numbers in bronchoalveolar lavage (BAL) fluid and lung tissue after the last antigen challenge in sensitised mice
Dex 0.01 OA
Dex 0.03 OA
Dex 0.1 OA
Dex 0.3 OA
Dex 1 OA
Dex 3 OA
0.6 ± 0.2
180.3 ± 34.6*
239.8 ± 76.5
129.9 ± 45.3
66.9 ± 20.6
43.6 ± 11.5*
4.6 ± 1.7*
3.6 ± 2.1*
0.7 ± 0.3
449.4 ± 76.7*
335.2 ± 93.9
218.8 ± 59.5
173.6 ± 46.8
38.5 ± 11.2*
29.8 ± 10.2*
104.4 ± 16.5
68.6 ± 12.7
79.9 ± 14.2
91.5 ± 14.2
57.0 ± 11.3
65.5 ± 5.5
71.7 ± 10.5
70.9 ± 4.7
10.2 ± 2.0
62.4 ± 8.5*
68.6 ± 19.5
52.2 ± 14.0
37.7 ± 9.2
25.8 ± 6.5
6.1 ± 1.0*
6.6 ± 1.6*
6.2 ± 1.8
80.4 ± 12.9*
111.5 ± 39.1
62.3 ± 18.0
37.4 ± 13.0
28.2 ± 6.7
5.6 ± 1.2*
6.9 ± 1.7*
823 ± 108
4944 ± 715*
5480 ± 1323
4033 ± 734
3479 ± 713
2703 ± 328*
2557 ± 519*
2739 ± 476*
4948 ± 622
21869 ± 2756*
22884 ± 4686
22261 ± 5450
16166 ± 2473
14520 ± 1767
15188 ± 1750
18619 ± 1805
571 ± 95
4721 ± 1277*
4590 ± 1266
3602 ± 754
2887 ± 841
2267 ± 714
689 ± 239*
311 ± 125*
367 ± 78
6889 ± 1316*
7946 ± 2196
5524 ± 1524
3923 ± 993
2737 ± 1168
304 ± 69*
196 ± 75*
1069 ± 98
8277 ± 1327*
8292 ± 2638
5912 ± 1696
3990 ± 959
3440 ± 959
707 ± 156*
691 ± 116.5*
In this study we have shown for the first time that there is dissociation between the dose of steroid needed to affect antigen-induced BAL and lung tissue eosinophilia and that needed to affect AHR. The ED50 dose of dexamethasone required to inhibit AHR is higher than that needed to inhibit eosinophilia. It is possible that eosinophilia has to be completely inhibited to have an effect on AHR; indeed, at 1 mg/kg dexamethasone, eosinophil infiltration into the BAL fluid following challenge is almost completely blocked and at the same dose AHR is also completely reversed. Lung tissue eosinophilia, however, is only inhibited by about 50% at 1 mg/kg dexamethasone, which further indicates the dissociation between eosinophilia and AHR. De Bie et al.  showed that dexamethasone (0.5 mg/kg) inhibited both antigen-induced AHR and airway eosinophilia in the mouse; however, using similar doses we found only an effect on eosinophilia. In the study by De Bie et al.  they administered the steroid intraperitoneally and employed a different way of measuring AHR, which might account for the difference.
Throughout the literature there are reports of various interventions that affect both allergic AHR and eosinophilia. Antibodies against interleukin-5 (IL-5) have been shown to inhibit both AHR and eosinophilia in the mouse [12–14]. Both allergic AHR and eosinophilia have been shown to be reduced in the following cases: in mice deficient in ICAM-1 (intercellular cell-adhesion molecule-1)  by treatment with an anti-B7-2 (CD86) monoclonal antibody [7, 16] and with an anti-CTLA4-IgG ; in Vβ8+-deficient mice and BALB/c mice treated with antibodies against Vβ8 ; in mice lacking a functioning 5-lipoxygenase enzyme ; in interferon-β-treated mice ; in IL-12 treated mice [21, 22]; and in mice treated with an immunosuppressive agent, FK-506 .
There are reports of interventions inhibiting allergic eosinophilia but not AHR: in humans, an IL-5-blocking monoclonal antibody ; in mice, antibodies against IL-5 [24–26] and IL-5 knockout animals . Other interventions have been shown to have the reverse effect, inhibiting allergic AHR without affecting eosinophilia: antibodies against interferon-γ in mice , antibodies against IL-16 in mice , IL-10-deficient mice  and mast-cell-deficient mice [24, 25]; Tournoy et al.  showed that by lowering the allergic challenge eosinophilia was lost but AHR remained.
Treatment with dexamethasone inhibited other leukocytes measured in the lung with ED50 values comparable to those determined for eosinophilia (Table 1). This would suggest that these inflammatory cells are also not associated with AHR; indeed, neutrophil numbers in the BAL fluid and tissue were not reduced to unchallenged levels by any dose of steroid used here (Table 2), whereas AHR was completely reversed. The involvement in AHR of other leukocytes measured here cannot be completely ruled out because it might be necessary to completely inhibit their infiltration into the lung before any impact on AHR is observed. Increased levels of macrophages, monocytes and lymphocytes in the lung were only completely inhibited at 1 mg/kg of dexamethasone, which is the corresponding dose needed to block AHR.
There is therefore a wealth of literature on the association between allergic eosinophilia and AHR that is sometimes confusing and contradictory. This is the first study that has addressed this question with a range of doses of corticosteroid, compounds known to block AHR and eosinophilia in all animal models of asthma and to affect inflammation and AHR in asthmatics in a clinical setting. We feel that this novel pharmacological approach has revealed a clear dissociation between eosinophilia and AHR in the same animal and this concurs with a study in humans showing no correlation between AHR and the number of inflammatory cells in sputum or bronchoalveolar lavage . These data question the rationale that many pharmaceutical and biotechnology companies have adopted in embarking on drug discovery programmes that target the eosinophil activation/infiltration signalling pathways (e.g. IL-5, VLA-4 and CCR-3).
These data suggest that other factors, such as airway wall remodelling, activation state of the eosinophils, T-cell activation or autonomic dysfunction, might be more important in the development of AHR.
Dissociation was observed between the dose of steroid needed to affect AHR compared with that required to affect inflammation, suggesting that AHR is not a direct consequence of eosinophilia. This novel pharmacological approach has revealed a clear dissociation between eosinophilia and AHR by using steroids that are the mainstay of asthma therapy. If the eosinophil is not associated with AHR, as this result suggests, the information described here is vitally important given that many pharmaceutical companies are engaged in developing low-molecular-mass compounds that target eosinophil activation/recruitment for the treatment of asthma.
- P enh :
We thank David Hele for his advice on the manuscript, and the Harefield Research Foundation and the British Heart Foundation for financial support.
- Brusasco V, Crimi E, Gianiorio P, Lantero S, Rossi GA: Allergen-induced increase in airway responsiveness and inflammation in mild asthma. J Appl Physiol 1990, 69:2209–2214.PubMedGoogle Scholar
- Wanner A, Abraham WM, Douglas JS, Drazen JM, Richerson HB, Ram JS: NHLBI Workshop Summary. Models of airway hyperresponsiveness. Am Rev Respir Dis 1990, 141:253–257.View ArticlePubMedGoogle Scholar
- Kirby JG, Hargreave FE, Gleich GJ, O'Byrne PM: Bronchoalveolar cell profiles of asthmatic and nonasthmatic subjects. Am Rev Respir Dis 1987, 136:379–383.View ArticlePubMedGoogle Scholar
- Bradley BL, Azzawi M, Jacobson M, Assoufi B, Collins JV, Irani AM, Schwartz LB, Durham SR, Jeffery PK, Kay AB: Eosinophils, T-lymphocytes, mast cells, neutrophils, and macrophages in bronchial biopsy specimens from atopic subjects with asthma: comparison with biopsy specimens from atopic subjects without asthma and normal control subjects and relationship to bronchial hyperresponsiveness. J Allergy Clin Immunol 1991, 88:661–674.View ArticlePubMedGoogle Scholar
- Battram C, Birrell M, Foster M, Webber SE, Belvisi MG: Comparison of inhaled spasmogen as determinants of airway hyperresponsiveness in a murine model of asthma. Br J Pharmacol 1999, 128:271P.Google Scholar
- Hamelmann E, Schwarze J, Takeda K, Oshiba A, Larsen GL, Irvin CG, Gelfand EW: Noninvasive measurement of airway responsiveness in allergic mice using barometric plethysmography. Am J Respir Crit Care Med 1997, 156:766–775.View ArticlePubMedGoogle Scholar
- Tsuyuki S, Tsuyuki J, Einsle K, Kopf M, Coyle AJ: Costimulation through B7–2 (CD86) is required for the induction of a lung mucosal T helper cell 2 (TH2) immune response and altered airway responsiveness. J Exp Med 1997, 185:1671–1679.View ArticlePubMedPubMed CentralGoogle Scholar
- Eum SY, Zuany-Amorim C, Lefort J, Pretolani M, Vargaftig BB: Inhibition by the immunosuppressive agent FK-506 of antigen-induced airways eosinophilia and bronchial hyperreactivity in mice. Br J Pharmacol 1997, 120:130–136.View ArticlePubMedGoogle Scholar
- Dohi M, Tsukamoto S, Nagahori T, Shinagawa K, Saitoh K, Tanaka Y, Kobayashi S, Tanaka R, To Y, Yamamoto K: Noninvasive system for evaluating the allergen-specific airway response in a murine model of asthma. Lab Invest 1999, 79:1559–1571.PubMedGoogle Scholar
- Underwood SL, Raeburn D, Lawrence C, Foster M, Webber S, Karlsson JA: RPR 10 a novel, airways-selective glucocorticoid: effects against antigen-induced CD4+ T lymphocyte accumulation and cytokine gene expression in the Brown Norway rat lung. Br J Pharmacol 6541, 122:439–446.View ArticleGoogle Scholar
- De Bie JJ, Hessel EM, Van AI, Van Esch B, Hofman G, Nijkamp FP, Van Oosterhout AJ: Effect of dexamethasone and endogenous corticosterone on airway hyperresponsiveness and eosinophilia in the mouse. Br J Pharmacol 1996, 119:1484–1490.View ArticlePubMedPubMed CentralGoogle Scholar
- Hamelmann E, Oshiba A, Loader J, Larsen GL, Gleich G, Lee J, Gelfand EW: Antiinterleukin-5 antibody prevents airway hyperresponsiveness in a murine model of airway sensitization. Am J Respir Crit Care Med 1997, 155:819–825.View ArticlePubMedGoogle Scholar
- Hogan SP, Koskinen A, Foster PS: Interleukin-5 and eosinophils induce airway damage and bronchial hyperreactivity during allergic airway inflammation in BALB/c mice. Immunol Cell Biol 1997, 75:284–288.View ArticlePubMedGoogle Scholar
- Cieslewicz G, Tomkinson A, Adler A, Duez C, Schwarze J, Takeda K, Larson KA, Lee JJ, Irvin C, Gelfand EW: The late, but not early, asthmatic response is dependent on IL-5 and correlates with eosinophil infiltration. J Clin Invest 1999, 104:301–308.View ArticlePubMedPubMed CentralGoogle Scholar
- Wolyniec WW, De Sanctis GT, Nabozny G, Torcellini C, Haynes N, Joetham A, Gelfand EW, Drazen JM, Noonan TC: Reduction of antigen-induced airway hyperreactivity and eosinophilia in ICAM-1-deficient mice. Am J Respir Cell Mol Biol 1998, 18:777–785.View ArticlePubMedGoogle Scholar
- Haczku A, Takeda K, Redai I, Hamelmann E, Cieslewicz G, Joetham A, Loader J, Lee JJ, Irvin C, Gelfand EW: Anti-CD86 (B7.2) treatment abolishes allergic airway hyperresponsiveness in mice. Am J Respir Crit Care Med 1999, 159:1638–1643.View ArticlePubMedGoogle Scholar
- Van Oosterhout AJ, Hofstra CL, Shields R, Chan B, Van Ark I, Jardieu PM, Nijkamp FP: Murine CTLA4-IgG treatment inhibits airway eosinophilia and hyperresponsiveness and attenuates IgE upregulation in a murine model of allergic asthma. Am J Respir Cell Mol Biol 1997, 17:386–392.View ArticlePubMedGoogle Scholar
- Hofstra CL, Van Ark I, Savelkoul HF, Cruikshank WW, Nijkamp FP, Van Oosterhout AJ: Vβ8+ T lymphocytes are essential in the regulation of airway hyperresponsiveness and bronchoalveolar eosinophilia but not in allergen-specific IgE in a murine model of allergic asthma. Clin Exp Allergy 1998, 28:1571–1580.View ArticlePubMedGoogle Scholar
- Irvin CG, Tu YP, Sheller JR, Funk CD: 5-Lipoxygenase products are necessary for ovalbumin-induced airway responsiveness in mice. Am J Physiol 1997, 272:L1053-L1058.PubMedGoogle Scholar
- Maeda Y, Musoh K, Shichijo M, Tanaka H, Nagai H: Interferon-β prevents antigen-induced bronchial inflammation and airway hyperreactivity in mice. Pharmacology 1997, 55:32–43.View ArticlePubMedGoogle Scholar
- Kips JC, Brusselle GJ, Joos GF, Peleman RA, Tavernier JH, Devos RR, Pauwels RA: Interleukin-12 inhibits antigen-induced airway hyperresponsiveness in mice. Am J Respir Crit Care Med 1996, 153:535–539.View ArticlePubMedGoogle Scholar
- Schwarze J, Hamelmann E, Cieslewicz G, Tomkinson A, Joetham A, Bradley K, Gelfand EW: Local treatment with IL-12 is an effective inhibitor of airway hyperresponsiveness and lung eosinophilia after airway challenge in sensitized mice. J Allergy Clin Immunol 1998, 102:86–93.View ArticlePubMedGoogle Scholar
- Leckie MJ, ten Brinke A, Khan J, Diamant Z, O'Connor BJ, Walls CM, Mathur AK, Cowley HC, Chung KF, Djukanovic R, Hansel TT, Holgate ST, Sterk PJ, Barnes PJ: Effects of an interleukin-5 blocking monoclonal antibody on eosinophils, airway hyper-responsiveness, and the late asthmatic response. Lancet 2000, 356:2144–2148.View ArticlePubMedGoogle Scholar
- Nagai H, Yamaguchi S, Maeda Y, Tanaka H: Role of mast cells, eosinophils and IL-5 in the development of airway hyperresponsiveness in sensitized mice. Clin Exp Allergy 1996, 26:642–647.View ArticlePubMedGoogle Scholar
- Kobayashi T, Miura T, Haba T, Sato M, Serizawa I, Nagai H, Ishizaka K: An essential role of mast cells in the development of airway hyperresponsiveness in a murine asthma model. J Immunol 2000, 164:3855–3861.View ArticlePubMedGoogle Scholar
- Hessel EM, Van Oosterhout AJ, Van Ark I, Van Esch B, Hofman G, Van Loveren H, Savelkoul HF, Nijkamp FP: Development of airway hyperresponsiveness is dependent on interferon-gamma and independent of eosinophil infiltration. Am J Respir Cell Mol Biol 1997, 16:325–334.View ArticlePubMedGoogle Scholar
- Coyle AJ, Kohler G, Tsuyuki S, Brombacher F, Kopf M: Eosinophils are not required to induce airway hyperresponsiveness after nematode infection. Eur J Immunol 1998, 28:2640–2647.View ArticlePubMedGoogle Scholar
- Hessel EM, Cruikshank WW, Van Ark I, De Bie JJ, Van Esch B, Hofman G, Nijkamp FP, Center DM, Van Oosterhout AJ: Involvement of IL-16 in the induction of airway hyper-responsiveness and up-regulation of IgE in a murine model of allergic asthma. J Immunol 1998, 160:2998–3005.PubMedGoogle Scholar
- Makela MJ, Kanehiro A, Borish L, Dakhama A, Loader J, Joetham A, Xing Z, Jordana M, Larsen GL, Gelfand EW: IL-10 is necessary for the expression of airway hyperresponsiveness but not pulmonary inflammation after allergic sensitization. Proc Natl Acad Sci USA 2000, 97:6007–6012.View ArticlePubMedPubMed CentralGoogle Scholar
- Tournoy KG, Kips JC, Schou C, Pauwels RA: Airway eosinophilia is not a requirement for allergen-induced airway hyperresponsiveness. Clin Exp Allergy 2000, 30:79–85.View ArticlePubMedGoogle Scholar
- Crimi E, Spanevello A, Neri M, Ind PW, Rossi GA, Brusasco V: Dissociation between airway inflammation and airway hyperresponsiveness in allergic asthma. Am J Respir Crit Care Med 1998, 157:4–9.View ArticlePubMedGoogle Scholar
This article is published under license to BioMed Central Ltd. This article is published in Open Access: verbatim copying and redistribution of this article are permitted in all media for any non-commercial purpose, provided this notice is preserved along with the article's original URL