Apoptotic cells overexpress vinculin and induce vinculin-specific cytotoxic T-cell cross-priming.

Here we show that apoptotic cells overexpress vinculin and are ingested by dendritic cells, which subsequently cross-prime vinculin-specific cytotoxic T lymphocytes (CTLs). Successful cross-priming requires that the apoptotic cells provide maturation signals to dendritic cells through CD40-CD40 ligand (CD40L) interactions. If apoptotic cells are CD40L-, the help of a third T cell is needed for priming, indicating a regulatory role for apoptotic cells in determining priming or tolerance. Vinculin-specific CTL priming is also related to apoptosis in vivo, given that in HIV-seropositive individuals, the frequency of specific CTLs depends on the proportion of peripheral CD40L+ apoptotic cells.

HIVgp120 activates autoreactive CD4-specific T cell responses by unveiling of hidden CD4 peptides during processing.

T cells are made tolerant only to those self-peptides that are presented in sufficient amounts by antigen-presenting cells. They ignore cryptic self-determinants, such as either those not generated by processing machinery or generated in insufficient amounts. It is anticipated that mechanisms that either change antigen processing or increase the yield of previously "invisible" peptides may be capable of inducing T cell priming and, if they are self-maintained, may sustain autoimmune diseases. Herein, we demonstrate for the first time a mechanism by which the gp120 human immunodeficiency virus-I, by downregulating plasma membrane CD4 and increasing its processing, unveils hidden CD4 epitopes, inducing an autoimmune-specific T cell response.

Transferrin receptor mediates uptake and presentation of hepatitis B envelope antigen by T lymphocytes.

Human activated T lymphocytes expressing class II molecules are able to present only complex antigens that bind to their own surface receptors, and thus can be captured, internalized, and processed through the class II major histocompatibility complex processing pathway. We have used the antigen-presenting T cell system to identify the viral receptor used by hepatitis B virus (HBV) to enter cells, as well as the sequence of HB envelope antigen (HBenvAg) involved in this interaction. Results show that both CD4+ and CD8+ T clones can process and present HBenvAg to class II-restricted cytotoxic T lymphocytes and that the CD71 transferrin receptor (TfR) is involved in efficient HBenvAg uptake by T cells. Moreover, we provide evidence that the HBenvAg sequence interacting with the T cell surface is contained within the pre-S2 region. Since TfR is also expressed on hepatocytes, it might represent a portal of cellular entry for HBV infection. This system of antigen presentation by T cells may serve as a model to study both lymphocyte receptors used by lymphocytotropic viruses and viral proteins critical to bind them.

Autoreactive cytotoxic T lymphocytes in human immunodeficiency virus type 1-infected subjects.

A subtractive analysis of peptides eluted from major histocompatibility complex (MHC) class I human histocompatibility leukocyte antigen (HLA)-A2.1 molecules purified from either human immunodeficiency virus type-1 (HIV-1)-infected or uninfected cells was performed using micro high-performance liquid chromatography and mass spectrometry. Three peptides unique to infected cells were identified and found to derive from a single protein, human vinculin, a structural protein not known to be involved in viral pathogenesis. Molecular and cytofluorometric analyses revealed vinculin mRNA and vinculin protein overexpression in B and T lymphocytes from HIV-1-infected individuals. Vinculin peptide-specific CTL activity was readily elicited from peripheral blood lymphocytes of the majority of HLA-A2.1+, HIV+ patients tested. Our observations suggest that atypical vinculin expression and MHC class I-mediated presentation of vinculin-derived peptides accompany HIV infection of lymphoid cells in vivo, with a resultant induction of antivinculin CTL in a significant portion of HIV+ (HLA-A2.1+) individuals.

Two brc-abl junction peptides bind HLA-A3 molecules and allow specific induction of human cytotoxic T lymphocytes.

Intracellular processing of the products of the bcr-abl junction region in CML Philadelphia chromosomes would generate novel peptides which, if they are capable of binding to HLA-class I molecules, would be potential targets of a cytotoxic T cell response. The 18 nonamers corresponding to the b2-a2 and b3-a2 fusions and differing from the parental bcr and abl sequences for at least one amino acid have been synthesized and tested for binding with HLA class I alpha chain preparations from HLA-homozygous B lymphoblastoid cell lines. Two peptides derived from the b3-a2 junction bound to HLA-A3 and elicited detectable specific CTL responses in vitro. The binding affinity of one of the two peptides could be increased by appropriate substitutions of the anchor residues with those of the known HLA-A3 anchor motifs. More important, the modified peptide had increased capacity to prime a specific CTL response in vitro. The interaction with HLA-A3 of these two peptides and their substitution derivatives seems to be promising for target trials aimed at eliciting a specific CD8 T cell response against CML.

Chronic hepatitis B virus and hepatitis C virus infections and cancer: synergy between viral and host factors.

Hepatitis B virus (HBV) or hepatitis C virus (HCV) infections represent major causes of chronic liver disease and hepatocellular carcinoma. Despite inducing shared pathological events leading to oncogenic transformation, these two viruses present profound differences in their molecular features, life cycle and interplay with host factors, which significantly differentiate the prognostic and therapeutic approach to the related diseases. In the present review, we report the main mechanisms involved in the multistep process leading from HCV/HBV infection and cancer development, discussing side-by-side the analogies and differences between the two viruses. Such events can be broadly categorized into (a) direct oncogenic effects, involving integration in the host genome (in the case of HBV) and chromosomal instability, interference with oncosuppressor pathways, induction of oxidative stress, promotion of angiogenesis, epithelial-mesenchymal transition, alterations in the epigenetic asset and interaction with non-coding RNAs; and (b) indirect activities mostly mediated by host events, including chronic inflammation sustained by peculiar cytokine networks (such as interleukin-6 and lymphotoxins), metabolic dysfunctions promoted by steatohepatitis, interplay with gut microbiota and fibrotic events (mainly in HCV infection). This scenario suggests that the integrated study of viral and host factors may lead to the successful development of novel biomarkers and targets for therapy.

Persisting viruses and autoimmunity.

Viral infections can be responsible for the onset and sustaining of autoimmune processes. We discuss how chronic inflammation associated with viral persistence is the prerequisite for initiation of a multi-step process leading to autoimmunity. Firstly, chronic inflammation may favor the priming of autoreactive T cells that have escaped thymic selection and are specific for self-mimicking viral peptides in the periphery. In addition, viral persistence and inflammation can act synergistically to induce and sustain autoimmunity either unveiling cryptic self-epitopes, or favoring determinant spreading, or activating dendritic cells, or promoting constant priming of new autoreactive T cells, or contributing to the efficient generation of effector cells, or, finally, restimulating memory T lymphocytes.

Enhanced production of interferon-gamma by T lymphocytes cloned from rejected kidney grafts.

Seventy-seven T cell clones were generated from cell blasts infiltrating rejected kidney allografts. All clones, either CD4 or CD8, displayed cytolytic activity evaluated by lectin-dependent cell-mediated cytotoxicity (LDCC) and natural killer activities. Furthermore, both types of clones were able to produce IFN-gamma following PHA stimulation. These data suggest that the graft infiltrate is characterized by T cell clones with cytolytic potential responsible for the killing of graft cells. The production of IFN-gamma, enhancing the class II MHC expression, may amplify the recipient immune response.

The immunology of HIV-infected long-term non-progressors--a current view.

Long-term non-progressors (LTNP) are human immunodeficiency virus (HIV)-infected individuals characterized by the absence of disease, low viral loads and stable or even increasing CD4(+) T cell counts for prolonged periods of time. In these subjects, an HIV-specific immune response which is either stronger or directed against a wider array of viral epitopes than that seen in progressors, can be often detected. Here, we summarize the characteristics of HIV-specific CD4(+) and CD8(+) T cell responses in LTNP, and discuss how a highly effective T cell-mediated immune response against HIV might contribute to the establishment of this particular condition.

Spreading of HIV-specific CD8+ T-cell repertoire in long-term nonprogressors and its role in the control of viral load and disease activity.

Long-term non-progressors (LTNP) represent a minority of human immunodeficiency virus (HIV) infected individuals characterized by stable or even increasing CD4+ T-cell count and by stronger immune responses against HIV than progressors. In this study, HIV-specific effector CD8+ T cells, as detected by both a sensitive ex vivo enzyme-linked immunospot (ELISPOT) assay and specific major histocompatibility complex (MHC) peptide tetramers, were at a low frequency in the peripheral blood of LTNP, and recognized a lower number of HIV peptides than their memory resting cell counterparts. Both factors may account for the lack of complete HIV clearance by LTNP, who could control the viral spread, and displayed a higher magnitude of cytotoxic T lymphocyte (CTL) responses than progressors. By combining cell purification and ELISPOT assays this study demonstrates that both effector and memory resting cells were confined to a CD8+ population with memory CD45RO+ phenotype, with the former being CD28- and the latter CD28+. Longitudinal studies highlighted a relatively stable HIV-specific effector repertoire, viremia, and CD4+ T-cell counts, which were all correlated with maintenance of nonprogressor status. In conclusion, the analysis of HIV-specific cellular responses in these individuals may help define clear correlates of protective immunity in HIV infection.

Infection of circulating and liver infiltrating T cells by hepatitis C virus of different subtypes.

Hepatitis C virus (HCV) infection display a very high rate of progression to chronicity and, like many other viruses causing persistent infections, it displays a tropism for the cells of the immune system. Peripheral blood mononuclear cells (PBMCs) from 21 HCV chronic carriers and long-term T cell clones derived from circulating or liver infiltrating T lymphocytes were tested by cDNA "nested" PCR for positive and negative strand HCV-RNA. The presence of HCV genomes in PBMCs is a frequent, although not constant, finding and can be accompanied by active viral replication, as suggested by the coexistence of negative strand HCV-RNA. Infected T cells are more represented in livers than in periphery, as indicated by comparing HCV-RNA detection in T cell clones isolated from both the compartments. Sequencing of viral genomes present in PBMCs and liver infiltrating lymphocytes showed that all the three major HCV genotypes present in our population of chronic carriers can infect lymphoid cells. Although each clonal population of T cells is infected by a single strain of HCV, in the same patient lymphoid cells can harbor different viral populations, different from those circulating at that moment in the serum.

Autoimmune T-cell response to the CD4 molecule in HIV-infected patients.

In a previous study, we demonstrated that by downregulating plasma membrane CD4 and increasing its processing, human immunodeficiency (HIV)-1-gp120 unveils hidden CD4 epitopes, inducing an in vitro anti-CD4-specific T-cell response. We report herein that this mechanism may potentially have important implications in HIV immunopathogenesis, because it could take part in the severe depletion of CD4+ cells that characterizes acquired immune deficiency syndrome (AIDS) and be related to disease progression. Freshly isolated peripheral blood lymphocytes (PBMC) from about 1/4 of a conspicuous cohort of HIV-infected patients responded to CD4 and this response was correlated with beta2-microglobulin levels, widely recognized as marker for progression of HIV infection. Moreover, we provide evidence that a CD4-specific T cell priming can occur in vivo, following a gp120 or anti-CD4 monoclonal antibody (mAb)-mediated CD4 molecule downregulation on antigen-presenting cells (APC). To our knowledge, this is the first study indicating that an autoimmune T-cell response is linked to HIV infection and that it could have an important impact on the immunopathogenesis of this disease.

Tumor necrosis factor-alpha and interferon-gamma synthesis by cerebrospinal fluid-derived T cell clones in multiple sclerosis.

T cell clones derived from cerebrospinal fluid (CSF) of patients with multiple sclerosis (MS) were analysed for their capacity to produce interleukin 2 (IL-2), interleukin 4 (IL-4), interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha). They were also compared with liver-infiltrating T cell clones from patients with chronic active hepatitis. All the CSF T clones (both CD4+ and CD8+) produced large amounts of IFN-gamma and particularly of TNF-alpha, that was synthesized in a significantly larger amount than compared clones. Moreover, they were capable of secreting IL-2, but not IL-4. From our results, we conclude that first, the CSF CD4+ T clones could constitute a subset with functional properties similar to the T helper 1 (Th1)/inflammatory cell subset of the mouse; and second, the large amounts of TNF produced by CSF T cell clones strongly suggests a significant role for this cytokine as well as of IFN-gamma in MS immunopathogenesis.

T cell recognition of hepatitis B envelope proteins.

We have studied the T-cell processing pathways of Hepatitis B antigens and the role of specific B lymphocytes. It could be shown that some form of processing by specific B cells is required for class I CTLs. This mechanism differs from class II endosomal processing. In addition, it could be shown that lysis of HBsAg-specific B cells may be partly responsible for chronic HBV carrier states.

Autoimmune chronic liver disease as a model of human autoimmunity.

Although clonal deletion and clonal energy have been demonstrated in transgenic mice, the findings that autoreactive B or T cells are present in healthy subjects suggest that they are not the sole mechanisms of tolerance. As regards helper T lymphocytes, tolerance to self-antigens can arise by preventing class II MHC expression on non-lymphoid cells and autoantigen presentation to helper T cells initiating the autoimmune response. Autoimmune chronic active hepatitis (CAH) seems to be a good model of self-tolerance bypass. Hepatocytes are able to express class II molecules and can perform accessory cell functions with respect to T cell clones generated from lymphocytes infiltrating the liver in autoimmune CAH patients. The class II antigen expression on hepatocytes may be modulated by IFN-gamma released by infiltrating T lymphocytes; thus, the activated liver cells can present autoantigens to autoreactive T cell clones. On the other hand, these findings may occur only when the upregulation of IFN-gamma or other lymphokines permits the expression of rare class II antigens on hepatocytes capable of binding particular residues of a liver-autoantigen which are recognized by specific autoreactive T cell clones binding different residues on the same epitope.

Class II MHC antigen expression on epithelial cells of salivary glands from patients with Sjögren's syndrome.

Class II MHC molecules are two-chain glycoproteins normally expressed only on the membrane of cells involved in the immune response. These molecules are restriction elements for helper T cells. Using indirect immunofluorescence on cryostat sections of biopsied salivary glands we have demonstrated epithelial expression of class II antigens in patients with Sjögren's syndrome. The HLA DR+ epithelial cells were seen in close proximity to lymphocyte infiltrates. The finding that class II molecules are also expressed in salivary glands without focal lymphocytic infiltrates suggests a "modulation" as opposed to "induction" of HLA DR antigens on epithelial cells in Sjögren's syndrome, the distinction being related to the enhancement of low levels of expressions vs. de novo synthesis.

Circulating HBsAg/IgM complexes in acute and chronic hepatitis B.

Complexes between HBsAg and IgM have recently been described in the sera of HBsAg carriers. A solid phase RIA for HBsAg/IgM complexes has been described. Fifteen patients with acute viral hepatitis type B, and 52 HBsAg chronic carriers were studied. Testing of serial sera in acute hepatitis patients revealed that HBsAg/IgM complexes disappeared (preceding HBsAg negativization and usually at the same time as seroconversion from "e" to "anti-e") with 4 weeks in all but one patient who became a chronic HBsAg carrier. In addition, HBsAg/IgM complexes were found in 48% of HBsAg chronic carriers, in 69% of CPH patients, but in only 20% of healthy carriers (p less than 0.005). Although complexes were detectable in 93% HBeAg positive chronic carriers, they were also frequently found in anti-HBe positive patients, but never in e/anti-e negative patients (p less than 0.001). HBsAg/IgM complexes seem to be of important prognostic and diagnostic value in acute and chronic hepatitis B.

HBeAg/anti-HBe system and development of primary hepatocellular carcinoma in patients with HBsAg-positive liver cirrhosis.

The significance of the HBeAg/anti-HBe system and other HBV markers in the evolution of HBsAg-positive liver cirrhosis to primary hepato-cellular carcinoma (PHC) was studied by following up 70 cirrhotic patients from February 1978 to February 1981. Eight out of 19 (42.1%) patients with HBsAg positive liver cirrhosis developed PHC. On the other hand, only 7.8% of the patients with HBsAg-negative liver cirrhosis developed PHC. In the HBsAg-positive group only the patients who had already seroconverted to anti-HBe (7 out of 11) or were negative for both HBeAg and anti-HBe (1 out of 3) at the time of first observation and showed a histological picture of inactive cirrhosis, developed PHC during the follow-up period. No HBeAg-positive cirrhosis showed such an evolution. The absence of HBeAg in the sera of patients who developed PHC suggests that active HBV replication becomes increasingly defective during the course of malignant transformation.

Normalization of depressed natural killer activity after interferon-alpha therapy is associated with a low frequency of relapse in patients with chronic hepatitis C.

In the present study, we found that human recombinant interferon-alpha (rIFN-alpha) given at a dose of 3 x 10(6) units thrice weekly for three months, and 1.5 x 10(6) units thrice weekly for the next three months, was able to restore depressed natural-killer (NK) activity to normal values in 12 out of 21 chronic hepatitis C patients positive for anti-HCV antibodies. In all of these patients, NK normalization was still sustained after three months from suspension of therapy. Eighteen patients also showed a normalization of the alanine aminotransferase (ALT) level by the end of treatment (responder patients), independently of changes in NK activity. No significant improvement in either NK activity or aminotransferase levels was seen among 20 untreated patients. In 8 responder patients (1 with normalized and 7 with low NK activity), ALT levels returned to pre-therapy values within three months after suspension of rIFN-alpha administration (relapse). We found that patients who normalized NK activity had a lower frequency of relapse as compared to patients with low NK activity by the end of treatment (p > 0.01). Immunofluorescence analysis of biopsy-derived liver tissue revealed that rIFN-alpha was able to induce strong MHC class I antigen expression on hepatocytes of treated patients, but this was not related to the clinical course.