Functional expression of transmembrane 4 superfamily molecules on human eosinophils

Background: Transmembrane 4 superfamily (TM4SF) molecules are exclusively f ound on hematopoietic cells. Several members of the TM4SF are reported to b e associated with other cell surface molecules, including integrins, and mi ght participate in signal transduction, but little is known about their rol e on eosinophils. In the present study, we determined the expression and fu nction of TM4SF molecules on human eosinophils. Methods: Surface expression of TM4SF molecules on purified peripheral blood eosinophils was examined u sing indirect immunofluorescence and flow cytometry. Purified eosinophils w ere incubated with anti-TM4SF monoclonal antibodies (mAbs) for up to 24 h. Eosinophil activation was evaluated by measuring eosinophil homotypic aggre gation as well as changes in surface expression of CD11b or CD62L by flow c ytometry. Results: Freshly isolated eosinophils expressed CD9, CD37, CD53, CD63 and CD81. Incubation with anti-CDS mAb but not with anti-CD37, CD53, C D63 or CD81: mAb induced significant eosinophil homotypic aggregation. Incu bation with any of the anti-TM4SF mAb for 30 min failed to alter the expres sion of either CD116 or CD62L on eosinophils. In contrast, the expression o f CD11b was significantly enhanced after 24 h of incubation with anti-CD53 mAb, while the expression of CD62L was significantly reduced with anti-CD81 mAb. Conclusions: Cross-linking of some surface TM4SF molecules induced si gnificant eosinophil homotypic aggregation, upregulation of CD11b expressio n, or CD62L shedding, consistent with activation of eosinophils. Our data s uggest that several TM4SF molecules are functionally expressed on human eos inophils, and therefore might participate in allergic inflammation.