ADHESION PROPERTIES OF MONO-MAC-6, A MONOCYTIC CELL-LINE WITH CHARACTERISTICS OF MATURE HUMAN MONOCYTES

Progress in the understanding of blood cell - endothelial cell interactions has been achieved by the development of in-vitro model systems. We describe adhesion properties of the recently established human monocytic cell line Mono Mac 6. These cells showed increased adherence to unstimulated and tumour necrosis factor (TNF)-alpha (50 U/ml) stimulated human umbilical vein endothelial cells (HUVEC) (9.4% +/- 0.4% and 56.5% +/- 3.3%), as compared to U937 cells (2.6% +/- 0.8% and 40.0% +/- 8.4%). The values were similar to freshly isolated human blood monocytes (18.8% +/- 7.5% and 55.7% +/- 9.3%, respectively). Maximal binding was 6.2 +/- 0.6 Mono Mac 6 cells per HUVEC, which was 34% less than U937 cells (8.9 +/- 0.3). The lower number of adherent Mono Mac 6 cells per HUVEC could be due to their larger size, as assessed by flow cytometry. Blocking experiments with monoclonal antibody (mAb) directed against E-selectin, VCAM-1 and ICAM-1 on HUVEC and CD 11b or CD14 on Mono Mac 6 cells demonstrated the contribution of these molecules to Mono Mac 6 adherence. Reduced binding after 24 h parallels the decline of E-selectin expression in HUVEC. Linearity of cell binding was confirmed from 0.2 x 10(6) to 1.0 x 10(6) Mono Mac 6 cells, Expression of CD11b and CD14 in Mono Mac 6 cells and in isolated human monocytes but not in U937 cells leading to interaction with ICAM-1 on HUVEC appears to be responsible for the increased adhesion of Mono Mac 6, as compared to U937 cells. In conclusion, Mono Mac 6 cells exhibit adhesion characteristics similar to human monocytes and therefore seem to be a cell line well suited for studying monocyte-endothelial cell interactions.