INTERLEUKIN-3 STIMULATES PROLIFERATION AND TRIGGERS ENDOTHELIAL-LEUKOCYTE ADHESION MOLECULE-1 GENE ACTIVATION OF HUMAN ENDOTHELIAL-CELLS

Proliferation and functional activation of endothelial cells within a tissue site of inflammation are regulated by humoral factors released by cells, such as T lymphocytes and monocytes, infiltrating the periva scular space. In the present study we investigated the effects of inte rleukin 3 (IL-3), an activated T lymphocyte-derived cytokine, on cultu red human umbilical vein endothelial cells (HUVEC). Proliferative acti vity, evaluated both by estimation of the fraction of cells in the S p hase and by direct cell count demonstrated that IL-3, at the dose of 2 5 ng/ml, enhances more than threefold both DNA synthesis and cell prol iferation above baseline control conditions. Binding studies with radi oiodinated ligand demonstrated that HUVEC constitutively express a sma ll number of IL-3 binding sites (approximately 99 binding sites per ce ll, with an apparent K(d) of 149 pM). Accordingly, molecular analysis showed the presence of transcripts for both alpha and beta subunits of the IL-3 receptor. Functional activation of endothelial cells was eva luated by the expression of the endothelial-leukocyte adhesion molecul e 1 (ELAM-1) transcript and by leukocyte adhesion. The ELAM-1 gene tra nscript was clearly detectable 4 h after IL-3 addition and started to decrease after 12 h. Moreover, IL-3-induced ELAM-1 transcription was f ollowed by enhanced adhesion of neutrophils and CD4+ T cells to HUVEC. The findings that IL-3 can stimulate both proliferation and functiona l activation of endothelial cells suggest that this cytokine can be in volved in sustaining the process of chronic inflammation.