Distinct spatial requirement for eosinophil-induced airways hyperreactivity

T helper (Th)-2-derived cytokines and their involvement in the recruitment and activation of inflammatory cells crucially orchestrate asthma pathogene sis. A notable cellular component of this allergy-induced inflammation is t he eosinophil. However, whether the eosinophil is an obligatory mediator fo r enhancing airways hyperreactivity (AHR) to cholinergic stimuli, a watersh ed of the asthmatic lung, is somewhat controversial. In this investigation we have endeavoured to define the spatial requirements for IL-4 and IL-13, and the downstream effector molecules, IL-5 and the CC chemokine eotaxin, f or the recruitment of eosinophils and the development of AHR in a murine mo del of allergic pulmonary disease. These studies are of particular importan ce considering clinical trials, with either the soluble IL-4R alpha subunit or a humanized anti-IL-5 antibody, are being conducted. Interestingly, our studies show that depletion of both IL-4 and IL-13 is necessary to ablate pulmonary eosinophilia and AHR, and that this may be attributed to the role these cytokines play in regulating the expression of the eosinophil-activa ting molecules, IL-5 and eotaxin. While it is clear that depletion of IL-5 diminishes pulmonary eosinophilia, we demonstrate in BALB/c mice that a def iciency in both IL-5 and eotaxin is necessary to abolish both the trafficki ng of eosinophils to the lung and AHR. However, in contrast to the neutroph il-rich inflammation observed in mice deficient in both IL-4 and IL-13, inf lammation per se in mice deficient in both IL-5 and eotaxin is significantl y attenuated. This suggests that asthma immunotherapy may be better directe d towards the eosinophil-activating molecules IL-5 and eotaxin, rather than towards pleiotrophic molecules such IL-4 and IL-13, which are additionally important in modulating alternative inflammatory responses.