EFFECT OF INTERLEUKIN-5 EXPOSURE DURING IN-VITRO EOSINOPHILOPOIESIS ON MAC-1 ADHESION MOLECULE EXPRESSION AND FUNCTION ON CULTURED HUMAN EOSINOPHILS

We examined the selective effects of interleukin (IL-5) in regulating the maturational expression of surface adhesion molecules on human eos inophils and adhesion to endothelial cells during eosinophilopoiesis i n vitro. Expression of the beta(2) integrins (CD11/CD18) and the beta( 1) integrin, VLA-4 (CD49d/CD29), was assessed during development in cu lture with IL-3, IL-5, and granulocyte-macrophage colony stimulating f actor in cultures of human umbilical cord blood-derived eosinophil (CD E) precursor cells. Expression of both CD11b and CD18 subunits of Mac- 1 was lower on CDE which were continuously (=chronically) exposed to I L-5 than on CDE which were cultured without IL-5 for the final week of culture. CD11b expression on cells grown without IL-5 was 71.3 +/- 5. 92 (mean specific fluorescence value [MSF] as measured by flow cytomet ry) versus 52.5 +/- 4.48 MSF for Mac-1 alpha (CD11b) on CDE grown in t he continued presence of 2 x 10(-11) mol/L IL-5 (P < .01). Although ex pression of VLA-4 decreased as CDE matured, expression of CD29 and CD4 9d were similar regardless of cytokine exposure for the final week of culture. For eosinophils cultured without IL-5, acute stimulation with 10(-9) mol/L IL-5 increased CD11b surface expression and increased th e number of cells adhering to unstimulated human umbilical vein endoth elial cells (HU-VEC) from 4,570 +/- 780 cells (9.14 +/- 1.56% adhesion ) to 8,385 +/- 515 cells (16.8 +/- 1.03% adhesion) (P < .01). Basal ad hesion to unstimulated HUVEC of CDE cultured continuously with IL-5 wa s comparable (8.62 +/- 1.12% adhesion; P = NS), but neither CD11b expr ession (50.3 +/- 11.8 MSF; P = NS v control) nor adhesion to HUVEC (6. 77 +/- 1.35%; P = NS) was enhanced in these eosinophils after acute st imulation with IL-5. Blockade of adhesion to IL-1-stimulated HUVEC cau sed by the anti-CD49d monoclonal antibody (ROoAb), HP2/1, was comparab le for cells cultured with IL-5 and without IL-5. However, the anti-CD 18 MoAb, R15.7, caused 47.6 +/- 5.08% inhibition of adhesion of eosino phils cultured without IL-5 and only 25.8 +/- 5.20% for cells cultured continuously with IL-5 (P < .01), and failed to block significantly t he adhesion of only the latter cells to IL-4-stimulated HUVEC. Our dat a show that continuous, chronic exposure to low concentrations of IL-5 causes decreased expression of Mac-1 and refractoriness to acute stim ulation with IL-5 of adhesion to HUVEC. These data further demonstrate that CDE maturing in the continued presence of IL-5 adhere to HUVEC p redominantly through VLA-4 ligation. (C) 1996 by The American Society of Hematology.