Unique sensitivities to cytokine regulated expression of adhesion molecules in human heart-derived endothelial cells

The expression of adhesion molecules by endothelial cells is crucial in many inflammatory processes and plays an active role in the development of reperfusion injury, acute and chronic rejection. The expression of adhesion molecules in different parts of the coronary tree to cytokine stimulation is not known. We describe here a detailed study of the effects of the inflammatory cytokines TNFalpha and IL-1beta on the expression of adhesion molecules vascular cell adhesion molecule-1 (VCAM-1), E-selectin and intracellular cell adhesion molecule-1 (ICAM-1) on human aortic root (HAEC), coronary artery (HCAEC) and heart microvascular (HHMEC)) endothelial cells in culture, using flow cytometry. We found constitutive levels of both VCAM-1 and E-Selectin on HCAEC and HHMEC (approximately 20%) which were significantly higher compared to HAEC (approximately 3%). There was an extreme sensitivity of HCAEC and HHMEC to 0.002 ng/ml TNFalpha: (VCAM-1 approximately 40%, E-Selectin approximately 25%) respectively, compared to HAEC (VCAM-1 approximately 5%, E-selectin approximately 5%). IL-1beta showed a similar pattern of expression at low doses (5 U/ml), but was less potent. We also observed prolonged expression of these adhesion molecules, especially on the HHMEC (>48 hours) compared to HAEC. There was also increased binding of peripheral blood mononuclear cells (PBMC) to both non-stimulated and TNFalpha stimulated HCAEC and HHMEC compared to HAEC. This data suggest that endothelial cells in different regions of the coronary tree express different patterns of basal and cytokine-stimulated adhesion molecule expression.

MHC class II expression on human heart microvascular endothelial cells: exquisite sensitivity to interferon-gamma and natural killer cells

BACKGROUND

Immunocytochemical analysis of human organs in situ reveals differential expression of MHC class II antigens by microvascular endothelial cells (MVEC) and endothelial cells (EC) from large vessels. In view of the role of EC as initiators of allograft rejection, it is of interest to understand the regulation of MHC class II regulation by human MVEC. We have previously isolated, cultured, and characterized MVEC from the human heart, showing that although these cells were initially MHC class II positive, the antigens were lost after about 14 days in culture. These results suggest that basal expression in vivo is maintained by circulating factors.

METHODS

Here we have compared the sensitivity of human heart MVEC, human umbilical vein endothelial cells (HUVEC), and adult large vessel EC (aorta, coronary artery, and pulmonary artery) to interferon (IFN)-gamma and natural killer (NK) cell-mediated induction of MHC class II antigens. MVEC and HUVEC were cultured with 1, 5, 10, 50, 100, and 500 U/ml of IFN-gamma for 4 days, the cells were washed, and flow cytometry was used to examine HLA-DR expression at days 1, 2, 4, 7, 10, 14, and 21. EC were also cultured with purified NK cells in the presence and absence of neutralizing antibodies to IFN-gamma, and MHC class II expression was analyzed.

RESULTS

As little as 5 U/ml of IFN-gamma produced 98% positive cells in heart MVEC compared with 100-500 U/ml needed for the same effect in HUVEC or other large vessel EC (coronary, aorta, pulmonary). Class II expression was maintained longer by MVEC (for 17 days) compared with HUVEC (for 10 days). NK cells and supernatant from MVEC/NK cultures induced MHC class II antigens on MVEC and HUVEC in a dose-dependent fashion; the MVEC showed an enhanced sensitivity compared with the HUVEC. The NK effects were inhibited by neutralizing antibodies to IFN-gamma. The allostimulatory ability of MHC class II-positive EC was shown to be proportional to the amount of MHC class II on the cell surface.

CONCLUSIONS

The results suggest that basal expression of MHC class II on human MVEC is maintained by circulating IFN-gamma and NK cells. This conclusion has implications for therapeutic interventions.

Alloproliferation of purified CD4+ T cells to adult human heart endothelial cells, and study of second-signal requirements

Human endothelial cells have been shown to be capable of causing direct allostimulation of T cells. However, the majority of immunological studies of human endothelial cells have been performed on cells of fetal origin. Here we use endothelial cells isolated from the adult human heart, both large vessel (coronary artery, pulmonary artery and aorta) and also microvascular. We have examined the ability of all these endothelial cells to cause direct allostimulation of T cells, and show that purified CD4+ T cells can proliferate in response to adult human heart endothelial cells, the response being dependent on pretreatment of the endothelial cells with interferon-gamma (IFN-gamma) and inhibited by anti-HLA-DR monoclonal antibody. The proliferative responses of CD8+ T cells to adult but not fetal endothelial cells was inconsistent and weak. Proliferative responses were not blocked by CTLA4-Ig, which inhibits T-cell responses to "classical' antigen-presenting cells (APC), but > 50% inhibition was achieved with monoclonal antibody to lymphocyte function-associated antigen-3 (LFA-3). These results show that adult human cardiovascular endothelial cells are capable of causing allostimulation of resting CD4+ T cells, using a different second signal to classical APC. In view of these findings endothelial cells should be considered as APC following solid organ transplantation.

Isolation, culture, and characterisation of MHC class II-positive microvascular endothelial cells from the human heart

Immunological studies of human endothelial cells have been performed almost entirely on endothelial cells (EC) derived from foetal (umbilical vein) or adult (aorta) large vessels. Immunologically these EC have in common the fact that they are negative for major histocompatibility complex (MHC) class II antigens (HLA-DR), in contrast to microvascular cells within the heart which are constitutively positive for HLA-DR antigens. Here we describe a simple method for isolating microvascular EC from chunks of adult human ventricle using antibody (anti-HLA-DR) or Ulex lectin-coated magnetic beads. Cytospins of primary isolates reveal the majority of cells binding the beads are CD31+ve, CD36+ve, and HLA-DR+ve. After 14 weeks in culture, 19% of cells remained HLA-DR+ve but CD36 expression had disappeared. Cultures after 4-7 passages were analysed by flow cytometry and immunocytochemical staining of cytospins with mAbs against conventional endothelial antigens (EN4, PECAM-1, vWF, uptake of acetylated LDL) and nonendothelial antigens (CD45, cytokeratin, alpha-actin, desmin, MHC class I and class II). The observation that all the cells remained positive for CD31 and did stain strongly for cytokeratin confirmed their endothelial origin. There was some persistent, albeit low level, expression of HLA-DR which was upregulated by interferon-gamma, showing kinetics of induction similar to that found on large vessel EC. These microvascular cells should be very useful for those wishing to compare microvascular with macrovascular EC and for immunological studies of heart endothelial cells.

Increased cyclosporine sensitivity of T cells from cord blood compared with those from the adult

Despite the increasing numbers of paediatric transplants performed, little is known about the immune responses of T lymphocytes in human neonates. Here we have compared the effects of cyclosporine on the phytohaemagglutinin (PHA) response of immature (cord) and mature (adult) lymphocytes using the following parameters of activation: (i) proliferation, measured by 3H-thymidine uptake; (ii) expression of cell surface IL-2 receptor; (iii) release of IL-2 into the supernatant. Cyclosporine was added to cultures of PHA-stimulated lymphocytes at doses ranging from 5 to 5000 ng/ml. The proliferative response of cord lymphocytes was considerably more sensitive to cyclosporine at each dose, so that 50% inhibition was achieved by 6 ng/ml and 21.5 ng/ml doses of cyclosporine on cord and adult lymphocytes, respectively. Expression of the IL-2 receptor by PHA-activated T cells and their subsets was assessed by flow cytometry. Cyclosporine inhibited IL-2 receptor expression to a significantly greater degree in cord CD4 and CD8 cells (49.7% and 70.1%) than in adults (17.9% and 30.0%). Biologically active IL-2 release was measured using the IL-2-dependent cell line CTLL-2. Cyclosporine at doses 50-5000 ng/ml produced 80-99% inhibition of both cord and adult responses. However, at very low doses (5 ng/ml) cyclosporine produced 69.3% inhibition of cord lymphocytes, compared with 42.0% of adult lymphocytes. These results suggest that the T cells of neonates are considerably more sensitive to cyclosporine than are adult T cells.

Nature of the mononuclear infiltrate and the mechanism of muscle damage in juvenile dermatomyositis and Duchenne muscular dystrophy

Normal skeletal muscle does not express class I MHC antigens. In contrast, these antigens are strongly expressed at the periphery of muscle fibres in patients with juvenile dermatomyositis (JDM) and Duchenne muscular dystrophy (DMD). Interferons can induce the expression of class I antigens, but in this study interferon-gamma could not be detected in JDM muscle biopsy specimens using four different immunocytochemical techniques. However, an infiltrate of mononuclear cells capable of synthesising interferons was present in biopsies from JDM and DMD patients. The predominant cell types detected in both diseases were macrophages and T lymphocytes, these two cell types comprising more than 80% of the infiltrating mononuclear cells. A striking predominance of CD4+ helper/inducer T cells was observed. The majority of these cells expressed class II MHC antigens and were, therefore, considered to be activated. Additional evidence for the functional activity of CD4+ T cells was derived from the finding that it was this population of cells from JDM biopsies which proliferated in response to interleukin-2 in vitro. T cell subsets in peripheral blood were also investigated in JDM and DMD patients. Only in the case of JDM were any significant differences from normal observed, where a significant reduction in the number of peripheral blood CD8+ T cells resulted in an elevation of CD4+/CD/8+ ratios. The role of CD4+ T cells and aberrant class I MHC antigen expression in mediating muscle damage in JDM and DMD is discussed.

Expression of class I and class II MHC antigens in neuromuscular diseases

The distribution of HLA class I and class II antigens has been investigated in cryostat sections of a series of 200 skeletal muscle biopsy specimens from patients with various neuromuscular disorders. Normal muscle fibres expressed no detectable class I antigens, whereas muscle fibres of patients with inflammatory myopathies and Duchenne (DMD) and Becker (BMD) muscular dystrophy showed consistently strong expression. In other neuromuscular diseases expression of class I antigens was more variable. No expression of class I antigens was observed on muscle fibres in samples from fetuses "at risk" for DMD and BMD or from female carriers of these disorders. The immunocytochemical assessment of HLA class I antigen expression was confirmed by a quantitative radioimmunoassay which demonstrated a 3-fold increase in the level of expression in muscle samples from patients with DMD and juvenile dermatomyositis. Class II antigen expression was never observed on muscle fibres in biopsies from normal individuals or any of the neuromuscular disorders. However, these antigens were expressed by endothelial cells present in these samples. Muscle specimens from fetuses and early in postnatal life showed very limited expression of class II antigens. They were expressed at a reduced level by about 3 months of age, but strong expression of class II antigens was not observed until about 1 year of age. The mechanism of induction of class I antigen expression in diseased muscle is not known. The appearance of class I antigens on diseased muscle may make the affected tissue a target for cytotoxic T cells and may thus have a role in muscle fibre damage in inflammatory myopathies and the X-linked muscular dystrophies.