Activation and transforming growth factor-β production in eosinophils by hyaluronan

To investigate whether extracellular matrix glycosaminoglycan hyaluronan (HA) modulates eosinophil activation and transforming growth factor (TGF)-beta production by eosinophils, human peripheral blood eosinophils (purity > 99%) from 12 patients with mild to moderate asthma or six healthy subjects were isolated and incubated with increasing concentrations of low molecular weight (mol wt) HA (approximate to 0.2 x 10(6) D) or high mol wt HA (3.0 to approximate to 5.8 x 10(6) D). We found that the low mol wt HA has a pronounced effect on eosinophil survival in both patients with asthma and healthy subjects in a dose-dependent fashion on Days 2 and 4. Whereas the high mol wt HA had a smaller effect on eosinophil survival than did the low mol wt HA. The HA-mediated eosinophil survival was partially but significantly inhibited ( approximate to 50% inhibition) by a blocking monoclonal antibody for CD44, a specific receptor of HA, and largely inhibited by an anti-granulocyte macrophage colony-stimulating factor (CM-CSF) neutralizing antibody but not by an anti-interleukin (IL)-3 or anti-IL-5 neutralizing antibody. In addition, the low mol wt HA increased CM-CSF messenger RNA (mRNA) expression and protein secretion by eosinophils in a dose-dependent fashion, suggesting that the HA-mediated eosinophil survival is due mainly to induction of CM-CSF release through partial CD44 signaling. Furthermore, we demonstrated that the low mol wt HA results in morphologic changes in eosinophils such as transforming from a round to a spindle shape and in homotypic aggregation, upregulates intercellular adhesion molecule-1 expression, and increases TGF-beta mRNA expression and protein secretion by eosinophils. These observations suggest previously unforeseen interactions between eosinophils and low mot wt extracellular matrix and, thus, novel pathways by which eosinophils may contribute to the regulation of airway inflammation and airway re-modeling.