Increased mature and immature CCR3 messenger RNA+ eosinophils in bone marrow from patients with atopic asthma compared with atopic and nonatopic control subjects.

Abstract

Eosinophil infiltration of the bronchial mucosa is characteristic of asthma. Eosinophils differentiate from CD34(+) progenitors. Animal models suggest cooperation between IL-5 and eotaxin to allow rapid mobilization of a pool of bone marrow eosinophils followed by recruitment to the airway mucosa. The purpose of this study was to enumerate CD34(+) cell numbers in blood and bone marrow from atopic asthmatics and control subjects and to test the hypothesis that there is an increased bone marrow pool of CCR3(+) eosinophils in patients with atopic asthma, as compared with control subjects. Bone marrow aspirates and peripheral blood were obtained from volunteers with asthma and control volunteers. CD34(+) cell numbers were evaluated by flow cytometry, and eosinophil colony-forming activity was evaluated by methylcellulose cultures. Mature eosinophils, eosinophil myelocytes, metamyelocytes, and band forms (immature eosinophils) were enumerated by morphologic findings and immunocytochemistry for eosinophil cationic protein. CCR3 and eotaxin mRNA expression was examined by in situ hybridization, and protein expression was examined by immunocytochemistry. CCR3(+) cells were further identified with Chromotrope 2R staining. CD34(+) cell numbers in bone marrow were increased in atopic subjects. Numbers of eosinophil colony-forming units in blood and bone marrow did not differ between groups. Percentages of both mature and immature eosinophils were increased in bone marrow from patients with atopic asthma, but not atopic patients with no asthma or normal control subjects. CCR3 was expressed by immature and mature bone marrow eosinophils. Eotaxin was expressed by bone marrow cells from all 3 groups, but there was no increase in subjects with asthma. These findings suggest that in humans there is an increased bone marrow pool of CCR3(+) mature and immature eosinophils available for rapid mobilization in subjects with asthma but not in atopic subjects with no asthma.