Different binding mechanisms of myeloid leukemic cells to adhesion molecules on bone marrow stromal fibroblasts induced by TNF-alpha and IL-4.

To study the mechanisms of adhesion of myeloid leukemic cells to bone marrow stroma, we analyzed the interaction of bone marrow stromal fibroblasts with myeloid leukemic cell lines and the modulation of adhesion molecule expression on stromal fibroblasts by TNF-alpha and IL-4. Like others, we found up-regulation of VCAM-1 and ICAM-1 on fibroblasts with TNF-alpha treatment, whereby IL-4 acted synergistically with TNF-alpha. VCAM-1 expression on the cell surface was maximal after 10 h, while ICAM-1 expression increased up to 48 h. All myeloid leukemic cell lines tested (HL-60, K562, TMM, U937, ML-2, PLB-985, THP-1, KG1a) revealed weak adhesion to untreated bone marrow fibroblasts (< or =10% bound cells). TNF-alpha and IL-4 significantly enhanced adhesiveness of fibroblasts to the cell lines PLB-985, THP-1, and ML-2, with a peak between 6 and 10 h of treatment. Adhesiveness to the cell line TMM was increased up to eightfold in a time-dependent manner for up to 48 h. The enhanced binding of ML-2-, THP-1-, and PLB-985 cells to stimulated fibroblasts was due at least partially to the interaction of VLA-4 with VCAM-1. Increased adhesion of TMM cells was impaired neither by antibodies to VLA-4, LFA-1, or Mac-1 nor by antibodies to their counter-receptors VCAM-1 or ICAM-1, suggesting that adhesion molecules distinct from VCAM-1 or ICAM-1 are involved in enhanced adhesiveness of the fibroblasts to myeloid leukemic cells.