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 perivascular space. In the present study we investigated the effects of interleukin 3 (IL-3), an activated T lymphocyte - derived cytokine, on cultured human umbilical vein endothelial cells (HUVEC). Proliferative activity, evaluated both by estimation of the fraction of cells in the S phase and by direct cell count demonstrated that IL-3, at the dose of 25 ng/ml, enhances more than threefold both DNA synthesis and cell proliferation above baseline control conditions. Binding studies with radioiodinated ligand demonstrated that HUVEC constitutively express a small number of IL-3 binding sites ( ∼ 99 binding sites per cell, with an apparent K_d f 149 pM). Accordingly, molecular analysis showed the presence of transcripts for both α and β subunits of the IL-3 receptor. Functional activation of endothelial cells was evaluated by the expression of the endothelial-leukocyte adhesion molecule 1 (ELAM-1) transcript and by leukocyte adhesion. The ELAM-1 gene transcript was clearly detectable 4 h after IL-3 addition and started to decrease after 12 h. Moreover, IL-3-induced ELAM-1 transcription was followed by enhanced adhesion of neutrophils and CD4⁺ T cells to HUVEC. The findings that IL-3 can stimulate both proliferation and functional activation of endothelial cells suggest that this cytokine can be involved in sustaining the process of chronic inflammation.