SUMMARYUsing a quantitative monolayer adhesion assay, the current report shows that treatment of human umbilical vein endothelial cells (HUVEC) with IL-6 increases their adhesiveness for blood lymphocytes, particularly CD4 cells, but not for polymorphonuclear cells and monocytes. This effect, which was most pronounced when using low concentrations of the cytokine (0 . 1-1 . 0 U/ml) and a short incubation period (4 h), was also apparent with microvascular endothelial cells and a hybrid endothelial cell line. Skin lesions from patients with mycosis fungoides contain high levels of IL-6, and blood lymphocytes from patients with this disorder also exhibited an enhanced adhesion to IL-6-treated HUVEC. The cytokine enhanced intercellular adhesion molecule-1 (ICAM-1) expression and induced the expression of vascular cell adhesion molecule-1 (VCAM-1) and E-selectin on endothelial cells. Antibody blocking studies demonstrated that the vascular adhesion molecules ICAM-1, VCAM-1 and E-selectin and the leucocyte integrin LFA-1 all contributed to lymphocyte binding to endothelium activated by IL-6. It is proposed that IL-6 may be involved in the recruitment of lymphocytes into non-lymphoid tissue.

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SUMMARYTo investigate the binding properties of dendritic cells (DC) to vascular endothelium, a comparative analysis was undertaken of DC, monocytes and lymphocytes isolated from the blood of 25 healthy subjects using monolayers of human umbilical vein endothelial cells as the adherence substrate. More blood DC (mean 24% adherence) were adherent to endothelial monolayers than monocytes (mean 18%; P < 0 . 001) and lymphocytes (mean 12%; P < 0 . 001). When the monolayers were pretreated with tumour necrosis factor-alpha (TNF-a) all leucocyte populations exhibited an increased attachment, but there was still greater binding of DC (mean 37% adherence) in comparison with monocytes (mean 23%; P < 0 . 001) and lymphocytes (mean 18%; P < 0 . 001). Flow cytometric analysis revealed that in relation to monocytes and lymphocytes the DC had a higher surface expression of the adhesion molecules CD11a (P < 0 . 05), CD11c (P < 0 . 005) and CD54 (P < 0 . 005) but a lower prevalence of cells bearing CD49d (mean 38%; P < 0 . 05) and the homing receptor CD62L (mean 14%; P < 0 . 001). CD1a was present on 22% of DC and virtually absent from the surface of monocytes and lymphocytes. The intensity of expression of the b 1 -integrins, CD49c, CD49d and CD49e was greater on DC than lymphocytes and monocytes (P < 0 . 05). Antibody blocking studies demonstrated that DC binding to untreated and TNF-a-treated endothelium was dependent upon the expression of CD11a, CD18 and CD49d, and the simultaneous application of anti-CD18 and anti-CD49d antibodies produced an approximate 70% inhibition of adhesion (P < 0 . 001). Thus, the expression of both b 1 -and b 2 -integrins contributes to the adhesive interaction between DC and endothelium.

This study addressed two questions; first, whether the supranormal adherence of blood lymphocytes from patients with multiple sclerosis (MS) to endothelial cell monolayers treated with tumour necrosis factor-alpha (TNF alpha) was a feature common to other inflammatory disorders; and second, whether the adherence properties of blood lymphocytes from MS patients were related to changes in disease activity and to levels of circulating TNF alpha and soluble adhesion molecules. In the first part of the investigation, lymphocytes from 14 patients with MS were more adherent to TNF alpha-treated endothelial cells (P < 0.01) than those from healthy controls, whereas the adherence properties of lymphocytes from 12 patients with rheumatoid arthritis, eight patients with psoriasis and ten patients with neurological diseases other than MS were normal. In the second phase of the work, measurement of the adhesive properties of lymphocytes isolated at monthly intervals from a further six MS patients over a 5-8 month period, found that changes in binding to TNF alpha-treated endothelial cells, directly paralleled changes in circulating levels of TNF alpha (r = 0.77; P < 0.001) and soluble vascular cell adhesion molecule-I (sVCAM-1) r = 0.67; P = 0.001). An increase in disease activity, measured by T2-weighted and gadolinium-enhanced magnetic resonance imaging of the central nervous system (CNS), occurred in two patients and was associated with heightened lymphocyte adhesiveness and a rise in serum TNF alpha levels. Further analysis of the 34 serum samples from the six MS patients revealed a direct relationship between the concentration of sL-selectin and soluble intercellular adhesion molecule-I (sICAM-I) (r = 0.65; P < 0.001) and between sL-selectin and sTNF alpha (r = 0.42; P < 0.02). These findings support the view that disease activity in MS is associated with an increased adhesive interaction of blood lymphocytes with vascular endothelium at inflammatory sites within the CNS.