Overexpression of CD44 on alveolar eosinophils with high concentrations of soluble CD44 in bronchoalveolar lavage fluid in patients with eosinophilic pneumonia

Background: High levels of interleukin-5 (IL-5) are found in the alveolar space of patients with eosinophilic pneumonia (EP). IL-5 promotes the growth and differentiation of eosinophils, as well as activating these cells. IL-5 also induces the expression of CD44 on eosinophils in vitro. To evaluate the contribution of CD44 to the pathogenesis of EP, we examined the expression of CD44 on eosinophils in bronchoalveolar ravage fluid (BALF) and measured the concentration of soluble CD44 (sCD44) in BALF from patients with EP. Methods: The concentrations of IL-5, sCD44, and hyaluronic acid (HA) were measured in BALF, The expression levels of CD44 on eosinophils in BALF and peripheral blood in patients with EP were compared, Results: The expression of CD44 on alveolar eosinophils and the concentration of sCD44 were increased in BALF of patients with EP, There was a significant correlation between IL-5 and sCD44 in BALF. A high concentration of HA was observed in BALF of EP patients. Conclusions: Our results suggest that the high expression of CD44 on eosinophils probably results from upregulation by IL-5 and could be important in the pathogenesis of EP.