Eotaxin is a chemokine with high potency and selectivity as a chemoattractant for eosinophils, and signals exclusively through the CCR3 receptor (Palframan et al., 1998). E otaxin is upregulated in the lungs, within three hours of antigen challenge (Jose et al, 1994), and eotaxin levels peak 6h post-allergen challenge in lung tissue and bronchoalveolar lavage fluid (Humbles et al, 1997). Eosinophils can promote inflammation, and their accumulation within the bronchial wall is a characteristic feature of asthma (Gleich et al, 2000). The effects of inhaled eotaxin have never been ascertained in asthmatic patients or animal models. This study therefore examined the effect(s) of eotaxin inhalation on airway function, in a guinea pig model of asthma, in order to establish if a bronchoconstrictor response, cell infiltration or airway hyperreactivity (AHR) can be produced.

Male Dunkin-Hartley guinea-pigs (300-350g) were sensitised with an i.p. injection of 100µg OA and 100mg Al₂OH₃ in 1ml of normal saline, on day 1 and day 5. All procedures commenced 12 – 16 days later. Guinea-pigs were exposed to aerosolised eotaxin (10µg/ml or 20µg/ml) in a sealed exposure chamber. Whole body plethysmography was used to monitor airway function before, and at intervals up to 24h post-challenge, recorded as specific airways conductance (sG_aw). Airway reactivity to 1mM histamine (20s, nose-only) was measured 24h before and after eotaxin challenge. BAL was carried out 24h after challenge so that total and differential cell counts could be recorded .

Sensitised animals exposed to 10 µg/ml eotaxin did not reveal a bronchoconstrictor response at any of the time points monitored. A late asthmatic response (LAR) was evident 6h after challenge with 20 µg/ml eotaxin, in both sensitised and non-sensitised guinea pigs, with mean (n=6) falls in sG_aw of –27.0 ± 5.3% and –32.3 ± 3.8%, respectively. Inhaled histamine did not induce bronchoconstriction 24h before any of the challenges. Exposure to 10 µg/ml eotaxin was not able to reveal a response to inhaled histamine 24h post-challenge, indicating no AHR. AHR was evident 24h after exposure to 20 µg/ml eotaxin, in both sensitised and non-sensitised animals, with falls in sG_aw of –32.5 ± 6.0% and –34.8 ± 10.6%, respectively. A significant increase in both total (4 fold) and differential (eosinophils 10 fold and macrophages 3 fold) cell counts was evident 24h after exposure to 20 µg/ml eotaxin when compared to saline challenges. Exposure to the lower dose of eotaxin (10 µg/ml) failed to increase cellular infiltration to the lung significantly.

It can therefore be concluded that exposure to eotaxin can reveal a LAR, AHR and cellular infiltration to the lung, possibly via the mobilisation of eosinophils from the bone marrow, and their recruitment to the airways. The release of their cytotoxic granules may therefore have initiated a cascade of events that led to the LAR and subsequent AHR, and the recruitment of more cells.

Gleich, G.J. et al (2000) The eosinophil and asthma. In Asthma and Rhinitis, edn 2
Humbles, A.A. et al (1997) J. Exp. Med.., 601-612
Jose, P.J. et al (1994) Biochem.Biophys.Res.Commun., 205, 788-794
Palframan, R.T. et al (1998) Blood, 91, 2240-2248

Supported by a BBSRC studentship to NS in collaboration with GlaxoSmithKline