Interleukin-5 (IL-5) is a
cytokine that preferentially effects the development and function of eosinophils, and is considered important in the pathophysiology of allergic
inflammation. In this study, we evaluated the ability of recombinant human
IL-5 (rHu IL-5) to promote tissue
eosinophilia and the importance of this
eosinophilia to pathological alterations in vascular function. Repetitive subcutaneous administration for 18 days of rHu
IL-5 resulted in a 7-fold increase in the number of eosinophils found in the ipsilateral hamster cheek pouch membrane. The contralateral cheek pouch membrane and peritoneum of these animals showed lesser but significant elevations in the number of eosinophils. In contrast, denatured rHu
IL-5 did not elevate eosinophils in these tissues. Through the use of intravital microscopy and fluorometric analysis, rHu
IL-5 treated hamster cheek pouch membranes were evaluated for alterations in microvascular permeability, using plasma clearance of
FITC-dextran 150 as an index. Despite promoting a prominent tissue
eosinophilia, the repetitive
subcutaneous injections of rHu
IL-5 did not alter the clearance of
FITC-dextran 150. Topical application of rHu
IL-5 to the cheek pouch, also, had no effect on the clearance of
FITC-dextran 150. Immunofluorescence observations using an antibody to the granule
protein,
eosinophil peroxidase, indicated that the recruited cells had not degranulated. Our results support the importance of
IL-5 in the recruitment of tissue eosinophils, but further stimulation is probably required to cause degranulation of these cells and the ensuing tissue damage.