A NOVEL FLOW CYTOMETRIC ASSAY FOR THE QUANTIFICATION OF ADHESION OF SUBSETS WITHIN A HETEROGENEOUS CELL-POPULATION - ANALYSIS OF LYMPHOCYTEFUNCTION-ASSOCIATED ANTIGEN-1 (LFA-1)-MEDIATED BINDING OF BONE-MARROW-DERIVED PRIMARY TUMOR-CELLS OF PATIENTS WITH MULTIPLE-MYELOMA

In a previous study the expression of the adhesion molecule LFA-1 on t umour cells in patients suffering from multiple myeloma (MM) was corre lated with growth of the malignant plasma cells in vivo. Here we descr ibe a novel in vitro flow cytometric adhesion assay (FCAA) which, base d on scatter and fluorescence properties, was used to analyse the cont ribution of the LFA-1/intercellular adhesion molecule-1 (ICAM-1) adhes ion pathway in the binding of bone marrow (BM)-derived LFA-1-positive primary tumour cells of patients with MM to interferon-gamma (IFN-gamm a)-activated, ICAM-1-positive, human venous umbilical endothelial cell s (huVEC) in vitro. To validate the FCAA, cells from different myeloma cell lines were labelled with the fluorescent dye CFDA or stained for CD38 expression, and LFA-1-mediated adhesion to IFN-gamma-activated e ndothelial cells was quantified. Results obtained with the FCAA were c ompared with a conventional adhesion assay employing Cr-51-labelled ce lls. Statistical analysis revealed that both assays gave similar resul ts. This allowed analysis of the contribution of LFA-1 to the adhesive potential of malignant plasma cells in bone marrow mononuclear cells (BMMC) from MM patients to IFN-gamma-activated endothelial cells. The results prove that LFA-1 expressed on bone marrow-derived plasma cells from MM patients can be used for cellular adhesion to ICAM-1 expresse d on adherent growing cells, and are suggestive for a role of the LFA- 1/ICAM-1 adhesion pathway in the pathophysiology of MM. The FCAA descr ibed in this study is a generally applicable assay, allowing analysis of the interaction of distinct subpopulations with in vitro grown adhe rent cells of different origin.