Expression and Purification of Secreted Forms of HSV Glycoproteins from Baculovirus-Infected Insect Cells

Herpes simplex virus (HSV) remains a major human pathogen worldwide (25 causing cold sores, eye and genital infections, blindness, encephalitis, and neonatal infections. Most adults have antibodies against the oral form of the virus HSV-1 (9), and a significant number are infected with the genital form, HSV-2. Both serotypes establish lifelong latent infections and reactivate periodically to produce recurrent disease (25). After infection, virus-encoded glycoproteins are expressed on all cellular membranes and are major targets of the host's immune response. The virion envelope contains 10 glycoproteins that are important for infection and pathogenesis of HSV-1 and HSV-2. Because HSV contains so many glycoproteins, sorting out their functions in virus entry remains a difficult task. Our approach has focused on establishing structure-function relationships of the individual glycoproteins with particular emphasis on gC and gD. After many years of studying the properties of these proteins in HSV-infected and plasmid-transfected mammalian cells, we have now begun to overexpress the proteins using a baculovirus expression system.

Immunogenicity of biliary epithelium: study of the adhesive interaction with lymphocytes

BACKGROUND & AIMS

Intrahepatic bile ducts express a range of lymphocyte adhesion molecules during episodes of inflammation. This may contribute to the susceptibility of biliary epithelium to immunologic damage during liver allograft rejection, graft-versus-host disease, and primary biliary cirrhosis. However, no previous study has shown that these adhesion molecules are functional. The aim of this study was to define the molecular basis of lymphoepithelial interactions within the intrahepatic bile ducts.

METHODS

Human intrahepatic biliary epithelial cells (HIBECs) were cultured, and their interaction with resting and activated lymphocytes was studied using a flow-cytometric assay that allowed characterization of the adherent cells and functional investigation of individual adhesive interactions. The capacity of adherent cytotoxic lymphoid cells to damage HIBEC was studied using a standard 51Cr release assay.

RESULTS

Allogeneic lymphocytes were bound by HIBECs; this adherence was increased by activation of either participating cell type. Cells with cytotoxic capacity were bound preferentially. At least 50% of the overall adhesion was dependent on lymphocyte function-associated antigen 1. Cytotoxicity assays showed that HIBECs were susceptible to lysis by lymphokine-activated natural killer cells.

CONCLUSIONS

This study shows that the adhesion molecules expressed by HIBECs are functional and necessary for the activity of cytotoxic effector lymphocytes.

T cell responses to tuberculin purified protein derivative in primary biliary cirrhosis: evidence for defective T cell function

BACKGROUND

Primary biliary cirrhosis (PBC) has an autoimmune aetiology, although little is known regarding the mechanisms of breakdown of self tolerance. One postulated mechanism of control of self tolerance is through interacting T cell subsets, a phenomenon explored in this study.

AIMS

To characterise and compare T cell subset responses to an antigen (tuberculin purified protein derivative derived from mycobacteria) in PBC patients and controls. Cross reactive responses to mycobacteria have recently been implicated in the aetiology of PBC.

SUBJECTS

58 PBC patients, 25 normal controls, and 34 chronic liver disease controls.

METHODS

Responses to antigen were measured in terms of primary T cell proliferation and cytokine secretion (by ELISA). Responding cells were phenotyped by FACS analysis.

RESULTS

Similar CD4+ T cell proliferative responses were seen in PBC patients (mean (SD) stimulation index (SI) 22.6 (27.2), 42 of 58 (72.4%) positive response), normal controls (46.5 (88.0), 17 of 25 (68%) positive), and chronic liver disease controls (24.8 (49.8), 27 of 34 (79.4%) positive)). Secretion of both interferon gamma and IL10 was significantly lower in PBC patients than controls (IFN gamma: PBC 822.7 (1100) pg/ml, controls 2929 (3402) pg/ml, p < 0.05: IL10: PBC 11.1 (15.6) pg/ml, controls 34.7 (63.4) pg/ml, p < 0.05).

CONCLUSIONS

In PBC unimpaired T cell proliferation is seen with reduced secretion of both Th-1 (interferon gamma) and Th-2 type (IL10) cytokines. These findings may result from differential subset responses and may help explain the defects of functional immunity seen in PBC.

Immunogenicity of biliary epithelium: investigation of antigen presentation to CD4+ T cells

The intrahepatic biliary epithelium is susceptible to extensive T-cell-mediated damage during primary biliary cirrhosis, primary sclerosing cholangitis, and hepatic allograft rejection. During these processes, human intrahepatic biliary epithelial cells (HIBEC) become activated and express high levels of the lymphocyte adhesion molecules, intercellular adhesion molecule-1 (ICAM-1) and lymphocyte-associated antigen (LFA)-3, and of class II MHC antigens. It follows that activated HIBEC may also play a direct role in the activation of antigen-specific CD4+ T lymphocytes. The capacity of class II MHC antigen-expressing HIBEC to present antigen and induce specific proliferation of CD4+ T cells was examined in this study. Lines of purified HIBEC were activated by culture with the proinflammatory cytokines interferon gamma (IFN-gamma) and tumor necrosis factor a and were mixed in coculture with allogeneic CD4+ T cells. The result of interaction between these cells was assessed by measurement of lymphoproliferation and IL-2 production. Class II MHC antigen-expressing HIBEC failed to induce either lymphoproliferation or IL-2 production. However, both of these parameters of T-cell activation were positive in cocultures when a costimulation signal was delivered to T cells by adding bivalent anti-CD28 antibodies. The antigen-specific activation of these T cells was further enhanced by the addition of a cross-linking secondary antibody that caused CD28 receptor aggregation. The failure of cytokine-stimulated HIBEC to induce T-cell activation is consistent with the observation that HIBEC do not express the costimulatory CD28 ligands B7-1 or B7-2 at either mRNA or protein levels. It may be concluded that HIBEC are unlikely to play a direct role in activation of antigen-specific CD4+ T lymphocytes within the inflamed liver.

Development of a flow cytometric assay to quantify lymphocyte adhesion to cytokine-stimulated human endothelial and biliary epithelial cells

The adhesive interaction between T lymphocytes and parenchymal cells is of importance for many processes of the cellular immune response. This adhesion is regulated by the activation status of the T cell and by cytokines in the microenvironment which can alter adhesion molecule expression by endothelial and epithelial cells. In this study results from an isotopic adhesion assay were compared with those from a flow cytometric assay in order to determine which was most appropriate for the investigation of lymphocyte adhesion to human umbilical vein endothelial cells (HUVEC) and intrahepatic biliary epithelial cells (HIBEC). Treatment of both these cell types with the proinflammatory cytokines interferon-gamma (IFN-gamma) or tumour necrosis factor-alpha (TNF-alpha) significantly upregulated expression of intercellular adhesion molecule-1 (ICAM-1). Treatment with TNF-alpha also induced endothelial cells to express vascular cell adhesion molecule-1 (VCAM-1). The isotopic assay demonstrated increased adhesion of lymphoblasts to HUVEC which had been stimulated with cytokines for 15 h but failed to detect major changes in adhesion following 72 h of cytokine treatment of HUVEC or HIBEC. However, the flow cytometric assay reproducibly demonstrated increased adhesion following cytokine treatment for both these time periods; these increases corresponded with the changes in adhesion molecule expression by cytokine-stimulated HUVEC and HIBEC targets. The differences in apparent adhesion measured by the two assays after cytokine stimulation for 72 h may be explained by cytokine-induced changes in the morphology and confluency of cultured cells. Results of the isotopic assay are proportional to the total number of lymphoid cells bound by the cultured target cells and will be distorted by changes in effective target cell area. The flow cytometric assay measures the mean number of lymphoid cells bound by each target cell and is independent of the total binding area. It is concluded that the flow cytometric assay is more suitable than the isotopic technique for following time-dependent changes in the adhesion of leukocytes to cytokine-stimulated target cells.

Hepatic allograft rejection: regulation of the immunogenicity of human intrahepatic biliary epithelial cells

Intrahepatic biliary epithelial cells were immunomagnetically purified from specimens of disaggregated human liver and were propagated in vitro. After three passes in culture, the cells were shown to be over 85% pure with contaminating leukocytes and endothelial cells constituting less than 2% of the population. Sensitive flow microfluorimetric analysis was performed after immunofluorescence labeling to quantify expression of both class 1 and class II major histocompatibility (MHC) antigens and the adhesion molecules intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and lymphocyte function-associated antigen-3 (LFA-3). It was shown that resting human intrahepatic biliary epithelial cells (HIBEC) expressed class 1 MHC antigens, ICAM-1, and relatively low levels of LFA-3. Stimulation with tumour necrosis factor-alpha (TNF-alpha) upregulated expression of ICAM-1, whereas Interferon-gamma (IFN-gamma) and a combination of IFN-gamma and TNF-alpha upregulated class I MHC antigens and ICAM-1 and induced class II MHC molecules. The level of expression of MHC antigens and of ICAM-1 and LFA-3 after stimulation of HIBEC with combined IFN-gamma and TNF-alpha was comparable with the expression of these antigens by an Epstein-Barr virus-transformed B-cell line. The phenotypic similarity between cytokine-stimulated HIBEC and a known antigen presenting cell is consistent with a potential role for biliary epithelial cells in antigen presentation.

Immunogenicity of biliary epithelial cells: study of the expression of B7 molecules

Efficient antigen presentation requires the provision of a co-stimulatory signal, the best characterized of which is provided by the B7 molecules. It is unclear whether biliary epithelial cells expressing Class II major histocompatibility complex molecules can function as antigen presenting cells, although this has been suggested as an important mechanism in the initiation and/or perpetuation of some immune-mediated liver diseases, including primary biliary cirrhosis and liver allograft rejection. We have found that human intrahepatic biliary epithelial cells do not express B7-1 (CD80) or B7-2 in vitro, even after activation with high doses of interferon-gamma, tumour necrosis factor-alpha or phorbol myristate acetate, or in vivo. However, they express similar levels of class II major histocompatibility complex antigens to those expressed by professional antigen presenting cells (Epstein-Barr virus transformed B cells). It is therefore unlikely that biliary epithelial cells stimulate efficient primary T cell activation. It may be possible that these non co-stimulatory class II major histocompatibility complex positive cells play a role in modulating immune responses in the liver.

CD4+ T cell subsets defined by isoforms of CD45 in primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is an autoimmune condition characterized by destruction of the intrahepatic bile ducts. Autoreactive CD4+ T cells have been reported both in the peripheral circulation and in the mononuclear cell infiltrate in the affected portal tracts. In this large study we have used two- and three-colour flow cytometry to determine the phenotypes of the CD4+ T cell subsets in the peripheral blood and liver-infiltrating lymphocytes of PBC patients (n = 43), normal controls (n = 19) and patients with alcoholic cirrhosis (n = 15), according to a novel classification based on the simultaneous expression of different isoforms of CD45. In PBC patients the proportion of peripheral blood CD4+ cells possessing the CD45ROhighRA- 'memory' phenotype was significantly increased, and the CD45RO-RAhigh 'naive' population was significantly decreased, compared with the two control groups. No significant differences in peripheral blood CD4+ T cell subsets were seen between patients with pre-cirrhotic and cirrhotic PBC. A similar, but more marked, shift towards the CD45ROhighRA- 'memory' phenotype was seen in the liver-infiltrating CD4+ T cells in PBC patients compared with alcoholic cirrhotics. Cells within the CD4+ memory subpopulation were further subgrouped according to expression of CD45RB, the level of expression of which has been associated with functional differences in the memory subset. In peripheral blood no differences were seen between PBC patients and controls with respect to the proportion of CD45ROhighRBhigh and CD45ROhighRBdim memory subsets. A statistically significant difference in the distribution of these memory subsets, with an increased memory-2/memory-1 ratio was observed in the liver-infiltrating CD4+ T cells of PBC patients compared with those from alcoholic cirrhotic patients. The potential implications of this observation are discussed.