Ectopic expression of IL-5 identifies an additional CD4+ T cell mechanism of airway eosinophil recruitment

CD4+ T cells have a critical role in the development of allergic pulmonary inflammation, including the recruitment of eosinophils to the airway lumen and interstitium. The expression of interleukin (IL)-5 by CD4+ cells has, in particular, often been lionized as the central link between allergic inflammation and the concomitant expansion or recruitment of eosinophils. The mechanism(s) by which CD4+ T cells mediates eosinophil recruitment was assessed with gene knockout mice deficient for T cells or T cell subtypes and a unique IL-5 transgenic mouse (line NJ.1726) that constitutively overexpresses this cytokine in the lung epithelium. Pulmonary IL-5 expression is significantly attenuated in T cell- and CD4+ but not CD8+ cell-deficient animals, suggesting an obvious explanation for the lack of eosinophils in the lungs of T cell-deficient and CD4(−/−) mice. However, although the constitutive expression of IL-5 in the lung epithelium of NJ.1726 mice elicited an eosinophilia in the airway lumen of both naive an...