CD34(+)/interleukin-5R alpha messenger RNA(+) cells in the bronchial mucosa in asthma: Potential airway eosinophil progenitors

Eosinophil differentiation is thought to occur by the action of interleukin (IL)-5 on CD34(+) progenitor cells. The allergen-induced increase in eosin ophil numbers in isolated airway preparations in vitro, and detection of in creased numbers of circulating CD34(+) cells in atopic subjects, led us to the hypothesis that the eosinophil infiltration of the airway in asthma may result from local mucosal differentiation, in addition to recruitment from the bone marrow. We examined CD34(+) cell numbers by immunohistochemistry and IL-5 receptor alpha (IL-5R alpha) messenger RNA (mRNA) expression by in sial hybridization in bronchial biopsies from atopic asthmatic patients, a nd from atopic and nonatopic control subjects. CD34(+) cell numbers were in creased in the airway in atopic asthmatic and atopic nonasthmatic subjects. In contrast, CD34(+)/IL-5R alpha mRNA(+) cells were increased in asthmatic subjects when compared with both atopic and nonatopic control subjects. Ai rway numbers of CD34(+)/IL-5R alpha mRNA(+) cells were correlated to airway caliber in asthmatic subjects and to eosinophil numbers. These findings su pport the concept that eosinophils may differentiate locally in the airway in asthma.