CD44 surface expression is increased on human eosinophils activated in vitro and in vivo

Activated eosinophils (EOS) are important effector cells in allergic and helminthic diseases. We hypothesized that changes in the levels of expression of cell surface antigens would accompany EOS activation. We therefore analyzed purified peripheral blood EOS by indirect immunofluorescence and flow cytometry for a panel of markers normally expressed on freshly isolated cells to determine if they become altered during culture for up to 72 hr with EOS survival-promoting cytokines (< 10 ng/ml of EL-3, IL-5, or GM-CSF, or up to 100 ng/ml IFN-y). Significant concentration- and time-dependent increases in CD44 expression were observed in EOS cultured with the hematopoietic growth factors IL 3, IL-5 or GM-CSF (= 2-3 fold increase in fluorescence intensity, p<0.05), while other constitutively expressed markers (e.g., CD49d, CDlla) remained unchanged. In contrast, IFN-Y had no effect on expression of CD44, even though similar levels of EOS viability were maintained. Simultaneous comparison of hypodense (specific gravity <1.085) and normodense EOS (specific gravity >1.085) from three donors by density gradient centrifugation revealed higher levels of CD44 expression (= 3-8 fold) on hypodense EOS. We conclude that hypodense EOS, and EOS activated in vitro with hematopoietic growth factors, have increased expression of CD44. The functional significance of these changes are being investigated.