Mechanisms of interference with the MHC class I-restricted pathway of antigen presentation by herpesviruses

Florid CD4+, CD56+ T-cell infiltrate associated with Herpes simplex infection simulating nasal NK-/T-cell lymphoma

We report a case of Herpes simplex virus (HSV) infection of the nasopharynx associated with a dense CD4+, CD56+ T-cell infiltrate that simulated lymphoma on clinical, histologic, and immunophenotypic grounds. Histologic examination showed a tumorlike lymphoid infiltrate with extensive necrosis. Multinucleated giant cells with "ground-glass" nuclei characteristic of HSV were observed in necrotic areas but were not prominent. Immunohistochemical studies of the lymphoid infiltrate revealed a predominance of T cells, positive for CD3, CD4, CD5, and CD56. Immunohistochemical staining with HSV antibody was focally positive in the multinucleated giant cells. Molecular studies using PCR and Southern blot were positive for HSV Type II. PCR studies for T-cell receptor gamma and immunoglobulin heavy chain gene rearrangements showed no evidence of a clonal population. In situ hybridization studies for Epstein-Barr virus (EBV) were negative. The clinical presentation of a large fungating mass, the extent of the lymphoid infiltrate, and the expression of CD56 all raised the possibility of a nasal NK/T cell lymphoma. However, the presence of HSV, lack of angioinvasion and angiodestruction, absence of EBV, and polyclonal T-cell nature of the infiltrate argued against this diagnosis. Although prior studies have not fully characterized the immunophenotypic features of the lymphocyte response to HSV in infected tissues, we postulate that the CD56+, CD4+ T-cell reaction represents a florid antiviral immune response.

Heat shock protein-peptide complexes elicit cytotoxic T-lymphocyte and antibody responses specific for bovine herpesvirus 1

Epitope-based vaccines offer a promising alternative to modified live vaccines against viruses such as herpesviruses which give rise to latent infections, and induce immunosuppression. The success of this approach depends on the ability to direct the CTL epitopes to the MHC class I antigen presentation pathway. The objective of this study was to evaluate the potential of the heat shock protein gp96 in this regard. A group of BALB/c mice was injected with three murine CTL epitope peptides of bovine herpesvirus 1 (BHV-1) complexed in vitro with bovine gp96 (gp96-peptides). Three other groups were injected with either the peptides alone, gp96 alone, or the peptides complexed with BSA. CTLs from mice immunized with gp96-peptides specifically lysed the peptide-pulsed syngeneic targets, as well as BHV-1-infected targets. CTLs from the other three groups did not lyse these targets. To further evaluate the utility of this approach, groups of BALB/c mice were immunized with gp96 isolated from a syngeneic cell-line transduced with BHV-1 glycoprotein D (BC-gD). Mice immunized with gp96 from BC-gD developed CTLs, as well as Abs specific for BHV-1 gD. Furthermore, in vitro stimulation of naive bovine PBMCs with gp96 from BC-gD resulted in CTLs specific for BHV-1. These results demonstrate the feasibility of using gp96-peptide complexes isolated from cells expressing BHV-1 proteins to induce CTL and Ab responses against BHV-1, without the prior knowledge of the CTL and Ab epitope sequences.

Monophosphoryl lipid A and QS21 increase CD8 T lymphocyte cytotoxicity to herpes simplex virus-2 infected cell proteins 4 and 27 through IFN-gamma and IL-12 production

We have shown previously that IFN-gamma pretreatment of human epidermal cells (ECs) cultured in vitro partially reverses down-regulation of surface MHC class I by HSV infection, allowing recognition by CD8 CTLs, and that HSV immediate early (IE)/early (E) proteins are the predominant targets for CD8 CTLs. In this study of 25 subjects, CD8 CTLs recognized the HSV-2 IE infected cell protein 27 (ICP27) (expressed in autologous IFN-gamma-pretreated, Vaccinia virus recombinant-infected ECs) in all subjects studied, ICP4 in 89%, and ICP0 in 11%. The main hierarchy of recognition was ICP27 > ICP4. ICP27 was the dominant target in 89% of subjects but showed great individual variability in the degree of cytotoxicity. CD8 cytotoxicity specific for HSV-2 IE proteins was enhanced by 48-67% when CD8 CTLs were coincubated with the combination of monophosphoryl lipid A and QS21 adjuvants at the time of Ag presentation. These adjuvants also significantly enhanced IL-12 and IFN-gamma production from nonadherent mononuclear cells stimulated by HSV-2-infected ECs. Addition of IL-12 and IFN-gamma at the time of initial Ag presentation enhanced CD8 cytotoxicity to levels comparable with those stimulated by the adjuvants. Addition of neutralizing Abs to IL-12 or IFN-gamma inhibited CD8 T cell cytotoxicity up to 95% when a combination of the Abs were added at the time of initial Ag presentation. Therefore, the mechanism for the enhancement of CD8 T cell cytotoxicity by adjuvants in this system appears to be via increased levels of IL-12 and IFN-gamma.

Phagocytic antigen processing and effects of microbial products on antigen processing and T-cell responses

Processing of exogenous antigens and microbes involves contributions by multiple different endocytic and phagocytic compartments. During the processing of soluble antigens, different endocytic compartments have been demonstrated to use distinct antigen-processing mechanisms and to process distinct sets of antigenic epitopes. Processing of particulate and microbial antigens involves phagocytosis and functions contributed by phagocytic compartments. Recent data from our laboratory demonstrate that phagosomes containing antigen-conjugated latex beads are fully competent class II MHC (MHC-II) antigen-processing organelles, which generate peptide:MHC-II complexes. In addition, phagocytosed antigen enters an alternate class I MHC (MHC-I) processing pathway that results in loading of peptides derived from exogenous antigens onto MHC-I molecules, in contrast to the cytosolic antigen source utilized by the conventional MHC-I antigen-processing pathway. Antigen processing and other immune response mechanisms may be activated or inhibited by microbial components to the benefit of either the host or the pathogen. For example, antigen processing and T-cell responses (e.g. Th1 vs Th2 differentiation) are modulated by multiple distinct microbial components, including lipopolysaccharide, cholera toxin, heat labile enterotoxin of Escherichia coli, DNA containing CpG motifs (found in prokaryotic and invertebrate DNA but not mammalian DNA) and components of Mycobacterium tuberculosis.

The effect of viruses on the ability to present antigens via the major histocompatibility complex

We describe viral pathogens that cause significant human disease by their ability to interfere with the expression of major histocompatibility complex class I and II molecules. Herpesviruses and papillomaviruses encode gene products that interfere with the class I pathway of antigen processing and/or peptide translocation. Adenoviruses encode unique gene products that interfere with transport of class I molecules. Influenza virus, measles virus, and HIV interfere with the class II pathway by either suppressing the production of class II molecules or impeding antigen trafficking. Cytomegalovirus interferes with both class I and class II pathways. Better understanding of these mechanisms may lead to further insight into the pathogenesis of viral infections and allow for improved treatments.

Identification of murine cytotoxic T-lymphocyte epitopes of bovine herpesvirus 1

Major histocompatibility complex (MHC) class I molecules present endogenously derived viral peptides to CD8+ cytotoxic T-lymphocytes (CTLs). The objective of this study was to identify the H-2Dd- and H-2Kd-restricted CTL epitopes of bovine herpesvirus 1 (BHV-1), based on the allele-specific peptide motifs (ASPMs) of the above class I molecules. Nine sequences conforming to the H-2Dd and H-2Kd ASPMs were identified on BHV-1 proteins, and the respective peptides were synthesized. Five of these peptides exhibited moderate to strong binding to the Dd molecule. CTLs generated by BALB/c mice immunized with BHV-1 proteins emulsified in a suitable adjuvant effectively lysed peptide-pulsed syngeneic targets, indicating that these epitopes were generated in vivo. Mice immunized with these peptides emulsified in a suitable adjuvant also developed anti-BHV-1 CTLs. These CTLs identified three veritable CTL epitopes among the "potential epitopes" synthesized based on the ASPMs. The elucidation of the CTL epitopes of BHV-1 should aid in the development of efficacious vaccines against this virus.

Viral persistence: mechanisms and consequences

Recent research has brought additional information on how virus products interfere with host cell antigen processing in vitro, new information on the interaction of virus with dendritic cells as a mechanism for alteration of immune responses - especially immunosuppression, and a preliminary proposal that nonretroviral RNA viruses might persist by utilizing host-cell reverse transcriptase to enter a DNA phase of replication.