The IL-5 receptor on human bronchus selectively primes for hyperresponsiveness

Area of Science:

• Immunology
• Respiratory Medicine
• Pharmacology

Background:

• The role of IL-5-induced eosinophilia in airway hyperresponsiveness is debated.
• Eosinophil-independent IL-5 effects on airway hyperresponsiveness have been observed in animal models.

Purpose of the Study:

• To investigate the direct effects of IL-5 on human bronchial responsiveness.
• To determine if IL-5 influences airway contractility independent of eosinophils.

Main Methods:

• Human bronchus, jejunum, and saphenous vein tissues were incubated with recombinant human IL-5 (rhIL-5).
• Contractility to acetylcholine and phenylephrine was measured.
• RT-PCR assessed IL-5 receptor alpha (IL-5Rα) and CCR3 expression in various tissues.

Main Results:

• rhIL-5 significantly enhanced bronchial contractility to acetylcholine in a dose-dependent manner.
• This effect was blocked by antibodies against IL-5 and IL-5Rα.
• rhIL-5 did not affect contractility in saphenous vein or jejunum.
• IL-5Rα expression was highest in bronchial muscle, with lower expression in other tissues.

Conclusions:

• IL-5 receptor expression is tissue-selective in airways.
• IL-5 can directly induce bronchial hyperresponsiveness, independent of eosinophils.
• Elevated IL-5 in asthma may directly contribute to bronchial hyperresponsiveness.