Expression of human interleukin-3 (multi-CSF) is restricted to human lymphocytes and T-cell tumor lines

While the cellular sources for granulocyte-macrophage colony- stimulating factor (GM-CSF) are known to be widely distributed among several cell types, interleukin-3 (IL-3) gene expression has been demonstrated in only certain T-cell clones and in blood mononuclear cells stimulated with phytohemagglutinin (PHA) and phorbol-myristate- acetate (PMA). To determine which blood cells were responsible for this expression, we fractionated PHA/PMA-stimulated mononuclear cells and identified T lymphocytes as the source of IL-3 mRNA. Low-level IL-3 expression was detected as well in several stimulated human T-cell lines. Hematopoietic stromal cells such as fibroblasts and endothelial cells could not be induced to express IL-3 mRNA. The kinetics of IL-3 mRNA induction in mononuclear cells and lymphocytes stimulated with PHA/PMA or anti-CD3 monoclonal antibody (MoAb) and interleukin-1 (IL-1) were similar to those observed for GM-CSF expression.     

Sickle reticulocytes adhere to VCAM-1

Adherence of sickle (SS) erythrocytes to endothelial cells represents interactions between red blood cell (RBC) and endothelial cell surface molecules. To enhance our understanding of the ligands involved, we transfected COS cells with the cDNAs of two endothelial cell adhesion molecules, VCAM-1 and E-selectin, and measured the binding of normal and sickle RBCs after static incubation. The percentage of COS cells with rosettes (five or more adherent RBCs) was determined. Normal RBCs did not adhere to VCAM-1-transfected COS cells. Unfractionated SS RBCs formed rosettes on the VCAM-1-transfected COS cells (mean +/- SD, 5.85% +/- 4.98%). Low-density SS RBCs were more adherent than high-density SS RBCs (P < .005). The adherent SS RBCs were a young reticulocyte population, staining positively for transferrin receptor. Another measure of reticulocyte age, RNA content, also correlated with adherence. SS RBC binding was specific--inhibitable by antibodies to either VCAM-1 or the alpha 4 integrin chain of VLA-4. In contrast, there was no significant adherence of normal or SS RBCs to E-selectin- transfected COS cells. These results suggest that young reticulocytes bind to endothelial cell VCAM-1 via VLA-4 integrin.