MHC-restricted cytotoxic T cells: studies on the biological role of polymorphic major transplantation antigens determining T-cell restriction-specificity, function, and responsiveness

Persistent HIV-1-Specific CTL Clonal Expansion Despite High Viral Burden Post In Utero HIV-1 Infection

To address the issue of clonal exhaustion in humans, we monitored HLA class I-restricted, epitope-specific CTL responses in an in utero HIV-1-infected infant from 3 mo through 5 years of age. Serial functional CTL precursor assays demonstrated persistent, vigorous, and broadly directed HIV-1 specific CTL activity with a dominant response against an epitope in HIV-1 Gag-p17 (SLYNTVATL, aa 77–85). A clonal CTL response directed against the immunodominant, HLA-A*0201-restricted epitope was found to persist over the entire observation period, as shown by TCR analysis of cDNA libraries generated from PBMC. The analysis of autologous viral sequences did not reveal any escape mutations within the targeted epitope, and viral load measurement indicated ongoing viral replication. Furthermore, inhibition of viral replication assays indicated that the epitope was properly processed from autologous viral protein. These data demonstrate that persistent exposure to high levels of viral Ag does not necessarily lead to clonal exhaustion and that epitope-specific clonal CTL responses induced within the first weeks of life can persist for years without inducing detectable viral escape variants.

Use of a high-affinity peptide that aborts MHC-restricted cytotoxic T lymphocyte activity against multiple viruses in vitro and virus-induced immunopathologic disease in vivo

Binding of a specific peptide(s) from a viral protein to major histocompatibility complex (MHC) class I molecules is a critical step in the activation of CD8(+) cytotoxic T lymphocytes (CTLs). Once activated, CTLs can cause lethal disease in an infected host, for example, by killing virus-containing ependymal and ventricular cells in the central nervous system or viral protein-expressing beta cells in the pancreatic islets of Langerhans. Here we describe the usage of a designed (not natural) high-affinity peptide to compete with viral peptide(s)-MHC binding. This peptide blocks virus-induced CTL-mediated disease both in the CNS and in the pancreatic islets in vivo. Further, the blocking peptide aborts MHC-restricted killing of target cells by CTLs generated to three separate viruses: lymphocytic choriomeningitis virus, influenza virus, and simian virus 40.

Dose Dependence of CTL Precursor Frequency Induced by a DNA Vaccine and Correlation with Protective Immunity Against Influenza Virus Challenge

Intramuscular injection of BALB/c mice with a DNA plasmid encoding nucleoprotein (NP) from influenza virus A/PR/8/34 (H1N1) provides cross-strain protection against lethal challenge with influenza virus A/HK/68 (H3N2). CTL specific for the H-2Kd-restricted epitope NP147–155 are present in these mice and are thought to play a role in the protection. To assess the effectiveness of NP DNA immunization in comparison with influenza virus infection in the induction of CTL responses, we monitored the frequency of CTL precursors (CTLp) in mice following i.m. injection with NP DNA or intranasal infection with influenza virus and showed that the CTLp frequency in NP DNA-immunized mice can reach levels found in mice that had been infected with influenza virus. We also measured the CTLp frequency, anti-NP Ab titers, and T cell proliferative responses in mice that were injected with titrated dosages of NP DNA and documented a correlation of the CTLp frequency and the Ab titers, but not proliferative responses, with the injection dose. Furthermore, we observed a positive correlation between the frequency of NP147–155 epitope-specific CTLp and the extent of protective immunity against cross-strain influenza challenge induced by NP DNA injection. Collectively, these results and our early observations from adoptive transfer experiments of in vitro activated lymphocytes from NP DNA-immunized mice suggest a protective function of NP-specific CTLp in mice against cross-strain influenza virus challenge.

The negative effect of repeated equine chorionic gonadotropin treatment on subsequent fertility in Alpine goats is due to a humoral immune response involving the major histocompatibility complex

In dairy goats, the use of eCG as a convenient hormone for the induction of ovulation is necessary for out-of-season breeding and artificial insemination. However, repeated eCG treatments are followed by decreased fertility in goats inseminated at a fixed time after treatment. In this report, we show the presence of anti-eCG antibodies in plasma of treated goats. A 500 IU eCG injection induces a humoral response, with variable concentrations of anti-eCG antibody being produced in individual goats. The analysis of successive anti-eCG immune responses over several years has demonstrated the existence of different populations of goats, defined as low, medium, and high responders. By the use of two caprine microsatellites located inside (OLADRB) and outside (BM1258) the major histocompatibility complex (MHC), a significant association (p < 0.05) between the anti-eCG antibody response and some MHC-DRB alleles was found. Goats with high antibody concentrations at the time of eCG injection (> 2.5 microg/ml) exhibited a much lower kidding rate than did other females (41.3% vs. 66.7%). Lower fertility of these goats, inseminated at a fixed time after eCG treatment, might be due to the observed delay in estrus occurrence and the preovulatory LH surge.

The discovery of T cell help for B cell antibody formation: a perspective from the 30th anniversary of this discovery

Thirty years ago, Miller and Mitchell described the bone-marrow origin of antibody-forming cells and the thymic origin of the help needed to activate the bone-marrow-derived antibody formation. Since then, there has been a continuous stream of discovery in Australia, from Zinkernagel and Doherty's description of MHC-restricted antigen recognition to Goodnow's dissection of the maturation and tolerization of antigen-specific B cells. All of these discoveries, and many more described in the text, contribute to the modern synthesis in immunology.

Anti-viral strategies of cytotoxic T lymphocytes are manifested through a variety of granule-bound pathways of apoptosis induction

Cytotoxic T cells and natural killer cells together constitute a major defence against virus infection, through their ability to induce apoptotic death in infected cells. These cytolytic lymphocytes kill their targets through two principal mechanisms, and one of these, granule exocytosis, is essential for an effective in vivo immune response against many viruses. In recent years, the authors and other investigators have identified several distinct mechanisms that can induce death in a targeted cell. In the present article, it is postulated that the reason for this redundancy of lethal mechanisms is to deal with the array of anti-apoptotic molecules elaborated by viruses to extend the life of infected cells. The fate of such a cell therefore reflects the balance of pro-apoptotic (immune) and anti-apoptotic (viral) strategies that have developed over eons of evolutionary time.

An inhibitor of HIV-1 protease modulates proteasome activity, antigen presentation, and T cell responses

Inhibitors of the protease of HIV-1 have been used successfully for the treatment of HIV-1-infected patients and AIDS disease. We tested whether these protease inhibitory drugs exerted effects in addition to their antiviral activity. Here, we show in mice infected with lymphocytic choriomeningitis virus and treated with the HIV-1 protease inhibitor ritonavir a marked inhibition of antiviral cytotoxic T lymphocyte (CTL) activity and impaired major histocompatibility complex class I-restricted epitope presentation in the absence of direct effects on lymphocytic choriomeningitis virus replication. A potential molecular target was found: ritonavir selectively inhibited the chymotrypsin-like activity of the 20S proteasome. In view of the possible role of T cell-mediated immunopathology in AIDS pathogenesis, the two mechanisms of action (i.e., reduction of HIV replication and impairment of CTL responses) may complement each other beneficially. Thus, the surprising ability of ritonavir to block the presentation of antigen to CTLs may possibly contribute to therapy of HIV infections but potentially also to the therapy of virally induced immunopathology, autoimmune diseases, and transplantation reactions.

Point mutation of a rubella virus E1 protein T-cell epitope by substitution of single amino acid reversed the restrictive HLA-DR polymorphism: a possible mechanism maintaining HLA polymorphism

The influence of single amino acid substitutions within a rubella E1 protein T-cell epitope, E1(273-284) on T-cell recognition was studied. Substitutions of an uncharged amino acid A for an E or for a T and substitution of a T for S were found to not significantly reduce the T-cell responses. However, substitution of a charged residue such as E for hydrophobic residues (I, V, or W); D for Q; or a relatively larger size amino acid for polar residues completely abolished the cytotoxicities mediated by E1(273-284)-specific T-cell clone. A set of single amino acid-substituted peptide analogs of E1(273-284) not eliciting cytotoxicity of the T-cell clone was used to test the influence of point mutation of the epitope on HLA DR restrictions. A panel of B-cell lines with different DR4 subtypes was used as targets in cytotoxicity assays to determine the restrictive HLA molecules. Results showed that modification of the T-cell epitope by point mutation could reverse the HLA DR restriction from one allele to other alleles. A model based on these results has been proposed to explain the mechanism balancing major histocompatibility complex (MHC) polymorphism in outbred populations.

Efficient class II major histocompatibility complex presentation of endogenously synthesized hepatitis C virus core protein by Epstein-Barr virus-transformed B-lymphoblastoid cell lines to CD4(+) T cells

The induction of an efficient CD4(+) T-cell response against hepatitis C virus (HCV) is critical for control of the chronicity of HCV infection. The ability of HCV structural protein endogenously expressed in an antigen-presenting cell (APC) to be presented by class II major histocompatibility complex molecules to CD4(+) T cells was investigated by in vitro culture analyses using HCV core-specific T-cell lines and autologous Epstein-Barr virus-transformed B-lymphoblastoid cell lines (B-LCLs) expressing structural HCV antigens. The T- and B-cell lines were generated from peripheral blood mononuclear cells derived from HCV-infected patients. Expression and intracellular localization of core protein in transfected cells were determined by immunoblotting and immunofluorescence. By stimulation with autologous B-LCLs expressing viral antigens, strong T-cell proliferative responses were induced in two of three patients, while no substantial stimulatory effects were produced by B-LCLs expressing a control protein (chloramphenicol acetyltransferase) or by B-LCLs alone. The results showed that transfected B cells presented mainly endogenously synthesized core peptides. Presentation of secreted antigens from adjacent antigen-expressing cells was not enough to stimulate a core-specific T-cell response. Only weak T-cell proliferative responses were generated by stimulation with B-LCLs that had been pulsed beforehand with at least a 10-fold-higher amount of transfected COS cells in the form of cell lysate, suggesting that presentation of antigens released from dead cells in the B-LCL cultures had a minimal role. Titrating numbers of APCs, we showed that as few as 10(4) transfected B-LCL APCs were sufficient to stimulate T cells. This presentation pathway was found to be leupeptin sensitive, and it can be blocked by antibody to HLA class II (DR). In addition, expression of a costimulatory signal by B7/BB1 on B cells was essential for T-cell activation.

Structural principles that govern the peptide-binding motifs of class I MHC molecules

The peptides that bind class I MHC molecules are restricted in length and often contain key amino acids, anchor residues, at particular positions. The side-chains of peptide anchor residues interact with the polymorphic complementary pockets in MHC peptide-binding grooves and provide the molecular basis for allele-specific recognition of antigenic peptides. We establish correlations between class I MHC specificities for anchor residues and class I MHC sequence markers that occur at the polymorphic positions lining the structural pockets. By analyzing the pocket structures of nine crystallized class I MHC molecules and the modeled structures of another 39 class I MHC molecules, we show that class I pockets can be classified into families that are distinguishable by their common physico-chemical properties and peptide side-chain selectivities. The identification of recurrent structural principles among class I pockets makes it possible to greatly expand the repertoire of known peptide-binding motifs of class I MHC molecules. The evolutionary strategies underlying the emergence of pocket families is briefly discussed.

In-vitro methods to decrease MHC class II-positive cells in retinal pigment epithelium cell grafts

Rejection of RPE transplants may be caused by expression of MHC class II molecules on the graft. We wanted to determine if passage level, hyperoxia, low temperature, or magnetic separation had an influence on this expression or on several other physiological parameters of bovine RPE cells. For this, bovine RPE cells were cultured under normal conditions for several passages (1-5) or were incubated with a high level of oxygen (75%) for 24 h or at low temperature (24 degrees C) for seven days. Magnetic beads coated with monoclonal antibody against MHC class II antigens were used to separate the positive cells from the total cell population. The number of MHC class II-positive RPE cells was not affected by increased passage, oxygen concentration, or low temperature. Using magnetic beads, approximately 7.5% of the cells were separated from the total RPE population as MHC class II-positive cells. Hyperoxia initially increased the number of RPE cells to 178% that of the untreated controls, but the subsequent MTT test showed a decrease in proliferation to 95% of control levels. Similarly, low temperature increased cell number of 110% that of controls, but prolonged proliferation decreased to 76% of the controls. None of the experimental conditions had a significant influence on the viability of the cells. Culture conditions can be modified to increase the yield of RPE cells, and MHC class II-positive RPE cells can be detected and selectively separated from the total cell population, both of which may prove to be useful for RPE cell transplantation.

Comparative expression of major histocompatibility complex (MHC) antigens on CD5+ and CD5- B cells in patients with chronic lymphocytic leukaemia (CLL)

The aim of this study was to investigate the expression of major histocompatibility complex (MHC) antigens on CD5+ and CD5- B cells of 13 patients with chronic lymphocytic leukaemia (CLL). This was carried out using a series of monoclonal antibodies (MAbs) against polymorphic and monomorphic class I and class II antigens, as well as to the transferrin receptor and assessed by flow cytometry and direct and indirect immunofluorescence. The expression of these molecules was assessed as mean fluorescent intensity (MFI). The results showed that cells from all 13 individuals expressed monomorphic class I antigens. The number of cases expressing polymorphic HLA-Bw6, -Bw4, -B7, -B27 and -A2 class I antigens on CD5- B cells was 11 (85%), 6(46%), 2(15%), 1(8%), 3 (23%), respectively, which was consistent with the expected population frequency distributions of these antigens. For each of the class I antigens on CD5+ and CD5- B cells, the ratio of the MFI was greater than 1 in 12 of 13 cases. For the transferrin receptor (CD71), this ratio was also almost always greater than 1. These results indicate that, unlike solid tumours where the loss or abnormal expression of class I and II antigens is a frequent event, the expression of class I antigens in CLL patients seems to be normal. This indicates that the loss of these antigens cannot provide the leukaemic cells with a selective advantage to escape immunological detection.

Assembly of MHC Class I Molecules with Biosynthesized Endoplasmic Reticulum-Targeted Peptides Is Inefficient in Insect Cells and Can Be Enhanced by Protease Inhibitors

To study the requirements for assembly of MHC class I molecules with antigenic peptides in the endoplasmic reticulum (ER), we studied Ag processing in insect cells. Insects lack a class I recognition system, and their cells therefore provide a “blank slate” for identifying the proteins that have evolved to facilitate assembly of class I molecules in vertebrate cells. H-2Kb heavy chain, mouse β2-microglobulin, and an ER-targeted version of a peptide corresponding to Ova257–264 were expressed in insect cells using recombinant vaccinia viruses. Cell surface expression of Kb-OVA257–264 complexes was quantitated using a recently described complex-specific mAb (25-D1.16). Relative to TAP-deficient human cells, insect cells expressed comparable levels of native, peptide-receptive cell surface Kb molecules, but generated cell surface Kb-OVA257–264 complexes at least 20-fold less efficiently from ER-targeted peptides. The inefficient assembly of Kb-OVA257–264 complexes in the ER of insect cells cannot be attributed solely to a requirement for human tapasin, since first, human cells lacking tapasin expressed endogenously synthesized Kb-OVA257–264 complexes at levels comparable to tapasin-expressing cells, and second, vaccinia virus-mediated expression of human tapasin in insect cells did not detectably enhance the expression of Kb-OVA257–264 complexes. The assembly of Kb-OVA257–264 complexes could be greatly enhanced in insect but not human cells by a nonproteasomal protease inhibitor. These findings indicate that insect cells lack one or more factors required for the efficient assembly of class I-peptide complexes in vertebrate cells and are consistent with the idea that the missing component acts to protect antigenic peptides or their immediate precursors from degradation.

Apoptotic cell death in response to dengue virus infection: the pathogenesis of dengue haemorrhagic fever revisited

BACKGROUND

Dengue virus infection may be asymptomatic or lead to undifferentiated febrile illness or dengue haemorrhagic fever and dengue shock syndrome (DHF/DSS). The major clinical manifestations of DHF/DSS are high fever, haemorrhage, hepatomegaly and circulatory failure.

OBJECTIVES

The relatively high level of viraemia only a few days after infection may reflect a large number of replication sites. However, the degree of cell injury in fatal cases of DHF/DSS is not sufficient to explain death and suggests metabolic disturbance rather than tissue destruction. This theory was investigated in this study.

RESULTS

We demonstrated that replication of dengue virus in infected cells induces stress leading to apoptotic cell death in vitro and in vivo.

CONCLUSIONS

The elimination of apoptotic bodies by phagocytic cells is a previously unsuspected pathway of dengue virus clearance from infected tissues. However, the mechanisms of host defence involving apoptosis and phagocytic cell activation may cause local tissue injury or transient homeostasis imbalance and may trigger further deleterious events.

Characterization of the cytolytic T-lymphocyte response to a candidate vaccine strain of equine herpesvirus 1 in CBA mice

The cytolytic T-lymphocyte (CTL) response to respiratory infection with equine herpesvirus 1 (EHV-1) in CBA (H-2(k)) mice was investigated. Intranasal (i.n.) inoculation of mice with the attenuated EHV-1 strain KyA resulted in the generation of a primary virus-specific CTL response in the draining mediastinal lymph nodes 5 days following infection. EHV-1-specific CTL could be restimulated from the spleen up to 26 weeks after the resolution of infection, indicating that a long-lived memory CTL population was generated. Depletion of CD8+ T cells by treatment with antibody and complement prior to assay eliminated CTL activity from both primary and memory populations, indicating that cytolytic activity in this model was mediated by class I major histocompatibility complex-restricted, CD8+ T cells. A single i.n. inoculation with KyA induced protective immunity against infection with the pathogenic EHV-1 strain, RacL11. The adoptive transfer of splenocytes from KyA-immune donors into sublethally irradiated recipients resulted in a greater than 250-fold reduction in RacL11 in the lung. The elimination of both CD4+ and CD8+ T cells from the transferred cells abrogated clearance of RacL11, while the selective depletion of either subpopulation alone had little effect. These results suggested that both lymphocyte subpopulations contribute to viral clearance, with either subpopulation alone being sufficient.

Expression and Characterization of Recombinant Soluble Peptide: I-A Complexes Associated with Murine Experimental Autoimmune Diseases

Structural and functional studies of murine MHC class II I-A molecules have been limited by the low yield and instability of soluble, recombinant heterodimers. In the murine autoimmune diseases experimental autoimmune encephalomyelitis and collagen-induced arthritis, MHC class II molecules I-Au and I-Aq present peptides derived from myelin basic protein and type II collagen, respectively, to autoreactive T cells. To date, systems for the expression of these two I-A molecules in soluble form for use in structure-function relationship studies have not been reported. In the present study, we have expressed functional I-Au and I-Aq molecules using a baculovirus insect cell system. The chain pairing and stability of the molecules were increased by covalently linking the antigenic peptides to β-chains and adding carboxyl-terminal leucine zippers. Peptide:I-Aq complex quantitatively formed an SDS-stable dimer, whereas peptide:I-Au formed undetectable amounts. However, the two complexes did not show any significant difference in their response to thermal denaturation as assessed by circular dichroism analyses. The autoantigen peptide:I-A complexes were highly active in stimulating cognate T cells to secrete IL-2 and inducing Ag-specific apoptosis of the T cells. Interestingly, the T cells were stimulated by these soluble molecules in the apparent absence of experimentally induced cross-linking of TCRs, indicating that they may have therapeutic potential in autoimmune disease models.

MHC class I heavy chain mRNA must exceed a threshold level for the reconstitution of cell surface expression of class I MHC complexes in cells transformed by the highly oncogenic adenovirus 12

In primary embryonal fibroblasts from transgenic mice expressing H-2(b) genes and a miniature swine class I transgene (PD1), transformation with adenovirus 12 results in suppression of assembly and cell surface expression of all class I complexes. Cell surface expression of PD1 can be recovered by transfecting the cells with peptide transporter genes. However, reconstitution of the H-2Kb gene expression requires, in addition, a 2-fold increase in the steady state level of the H-2Kb mRNA that can be attained by treatment of the cells with interferons or by transfecting them with the H-2Kb gene. A detailed analyses of the biogenesis of class I molecules has revealed the steady state expression of free class I heavy chains that are not converted into conformed complexes even when peptide transporter genes are overexpressed. The fact that class I complex assembly seems to be highly inefficient in certain cell lines might be a major in vivo obstacle for the elimination of transformed or virus-infected cells by cytotoxic T lymphocytes, especially in view of the fact that the level of class I gene transcription is often down-regulated in cancer cells and/or that assembly of class I major histocompatibility complexes can be subverted by virus-encoded proteins.

Induction and exhaustion of lymphocytic choriomeningitis virus-specific cytotoxic T lymphocytes visualized using soluble tetrameric major histocompatibility complex class I-peptide complexes

This study describes the construction of soluble major histocompatibility complexes consisting of the mouse class I molecule, H-2Db, chemically biotinylated beta2 microglobulin and a peptide epitope derived from the glycoprotein (GP; amino acids 33-41) of lymphocytic choriomeningitis virus (LCMV). Tetrameric class I complexes, which were produced by mixing the class I complexes with phycoerythrin-labeled neutravidin, permitted direct analysis of virus-specific cytotoxic T lymphocytes (CTLs) by flow cytometry. This technique was validated by (a) staining CD8+ cells in the spleens of transgenic mice that express a T cell receptor (TCR) specific for H-2Db in association with peptide GP33-41, and (b) by staining virus-specific CTLs in the cerebrospinal fluid of C57BL/6 (B6) mice that had been infected intracranially with LCMV-DOCILE. Staining of spleen cells isolated from B6 mice revealed that up to 40% of CD8(+) T cells were GP33 tetramer+ during the initial phase of LCMV infection. In contrast, GP33 tetramers did not stain CD8+ T cells isolated from the spleens of B6 mice that had been infected 2 mo previously with LCMV above the background levels found in naive mice. The fate of virus-specific CTLs was analyzed during the acute phase of infection in mice challenged both intracranially and intravenously with a high or low dose of LCMV-DOCILE. The results of the study show that the outcome of infection by LCMV is determined by antigen load alone. Furthermore, the data indicate that deletion of virus-specific CTLs in the presence of excessive antigen is preceded by TCR downregulation and is dependent upon perforin.

Cellular and molecular aspects of thymic T-cell education in neuroendocrine self principles. Implications for autoimmunity

Thymic epithelial and nurse cells from different species express a repertoire of neuroendocrine polypeptide precursors. This repertoire exerts a dual role in T-lymphocyte selection according to their status either as cryptocrine signals or as neuroendocrine self-antigens of the peptide sequences that are processed from those precursors then presented to pre-T cells. Thymic neuroendocrine self-antigens correspond to peptide sequences highly conserved throughout evolution of their family. Though thymic MHC class I molecules are involved in the processing of thymic neuroendocrine self-antigens, preliminary data show that their presentation to pre-T cells is not allelically restricted. Thymic T-cell education in neuroendocrine families also implies that the structure of a given family may be presented to pre-T cells. Our studies have evidenced the homology between thymic neuroendocrine-related self-antigens and dominant T-cell epitopes of peripheral neuroendocrine signals (neuroendocrine autoantigens). The biochemical difference between neuroendocrine autoantigens and homologous thymic self-antigens might explain the opposite immune responses evoked by those two types of antigens (activation and memory induction vs. tolerogenic effect). Altogether, these studies support the therapeutic use of thymic neuroendocrine self-antigens in reprogramming the immunological self-tolerance that is broken in autoimmune endocrine diseases like insulin-dependent diabetes type I. As recently stated by P. M. Allen in an important review, the fate of developing T lymphocytes in the thymus is influenced by the numerous types of peptidic interactions within the thymic cellular environment. To define the precise nature of thymic cells and naturally occurring biochemical peptide signals involved in positive and negative selection of immature T cells has become a prominent objective for the future research efforts in thymic physiology. This paper will try to show how thymic neuroendocrine-related peptides synthesized and processed within the thymic microenvironment indeed can play a role both in the development of the peripheral T-cell repertoire and in the death of randomly rearranged, self-reactive T cells.

Activation Requirements, Lytic Mechanism, and Development of a Novel Anti-CD8-Resistant CTL Population

Almost all conventional CD8+ CTL and their CD8+ precursors are inhibited by anti-CD8 mAb. This requirement for CD8 function reflects both an avidity-augmentation role and a signal-transduction role for CD8 on T cells. We have, however, previously identified and partially characterized a novel functional population of CD8+, but anti-CD8-resistant, MHC class I-allospecific CTL. These CTL have unusual activation requirements in that their efficient generation in vitro requires inhibition of the CD8 avidity contribution (but not the CD8 signaling contribution), by anti-CD8 mAb. In this study, we have investigated the relationship of anti-CD8-sensitive and anti-CD8-resistant CTL by several criteria. These CTL populations share the phenotypic markers we have tested to date, they have similar but not identical Ag-specific repertoires, and they both appear to be generated from naive unprimed T cells. However, anti-CD8-sensitive and anti-CD8-resistant CTL populations exhibit important functional differences. They differ in their kinetics of activation in vitro, their dependence on exogenous cytokines, their use of lytic effector mechanisms, and their tissue distribution during ontogeny. Based on these results, we favor the hypothesis that these CTL populations represent distinct T cell lineages or subsets, and not merely different TCR avidity ranges within a single T cell lineage or subset.

Fas- and perforin-independent mechanism of cytotoxic T lymphocyte

Cytotoxic T lymphocytes (CTLs) play an important role in elimination of virus-infected cells (1). Recent studies revealed at least two distinct mechanisms that CTLs utilize to destroy their target cells. Both mechanisms induce target cell apoptosis specifically and directionally, but these processes are totally different. One is pore formation on target cell membrane by perforin secreted from CTLs (perforin-granzyme pathway), and the other is ligation of Fas, which is expressed on the surface of target cells and Fas ligand, on the surface of CTLs (Fas-FasL pathway) (2). Here we review our work and describe CTL clones that have novel lytic mechanisms derived from CD4-CD8- lymph node cells of gld mice.

Activation of influenza-specific memory cytotoxic T lymphocytes by Concanavalin A stimulation

Traditionally, the in vitro activation of virus-specific memory cytotoxic T lymphocytes (CTLs) has been achieved by stimulating the CTLs with antigen-presenting cells (APCs) infected with an appropriate virus or pulsed with virus-specific antigenic peptides. Here, we describe the utilization of the polyclonal activator Concanavalin A (ConA) for in vitro restimulation of memory CTLs from virus-primed mice. Using this simple method, the activation of splenocytes with ConA for 3 days (i) eliminates the need to stimulate with virus-pulsed APCs and (ii) generates CD8+ CTLs that exhibit virus specificity and MHC-restricted lytic activity similar to CTLs obtained by conventional viral restimulation. In vitro ConA stimulation of splenocytes from BALB/c mice primed with the A/Texas/77 or A/Japanese/57 strain of influenza virus and from C57L/J mice infected with the A/Texas strain, generated CTLs with specific lytic activity. Hence reactivation of memory CTLs by this method is a general phenomenon rather than a mouse or viral strain-specific one. The ConA stimulation method used here had a recall of long-term (1 year) memory CTLs that effectively lysed virally infected targets. Further ConA-stimulated effector lymphocytes from virally primed animals have been shown to recognize and subsequently lyse target cells pulsed with virus or virus-derived peptides. The ConA reactivation of specific anti-viral CTLs may facilitate (i) studying anti-viral CTL responses and (ii) identifying of viral epitopes when unknown or when appropriate viral stimulation is impossible.

Clearance of an influenza A virus by CD4+ T cells is inefficient in the absence of B cells

The primary CD8+ T-cell response protected most B-cell-deficient muMT mice against intranasal infection with the HKx31 influenza A virus. Prior exposure did not prevent reinfection upon homologous challenge, and the recall CD8+ T-cell response cleared the virus from the lung within 7 days. Depleting the CD8+ T cells substantially reduced the capacity of these primed mice to deal with the infection, in spite of evidence for established CD4+ T-cell memory. Thus, the control of this relatively mild influenza virus by both primary and secondary CD4+ T-cell responses is relatively inefficient in the absence of B cells and CD8+ T cells.

Relationship between HLA antigens and infectious agents in contributing towards the development of Graves' disease

Graves' disease (GD) is an autoimmune thyroid disorder which is associated with the human leucocyte antigens HLA-DR3 and DQA1* O501 in Caucasians. We have explored the possibility that some patients with certain HLA specificities develop anti-HLA antibodies which are correlated with environmental factors that may contribute to the development of GD. We studied 40 GD patients and 157 healthy individuals (controls). Serology was used to type HLA-A, -B, -Cw, and -DR antigens. The frequencies of these antigens in relation to lymphocytotoxic anti-HLA-A-B-Cw-DR antibodies and two environmental factors (Yersinia enterocolitica and Coxsackie B virus) were determined. The frequencies of HLA-B15, -B21 and DR3 antigens were increased, whereas HLA-DR5 antigen was decreased in GD patients. A significant association between HLA-DR3 antigen and lymphocytotoxic antibodies was observed, i.e., IgGs from GD patients were cytotoxic to HLA-DR3+ normal B cells. Following absorption with Yersinia enterocolitica or Coxsackie-B-virus, only Coxsackie-B virus completely inhibited the lymphocytotoxic reactions against HLA-DR3+ B cells. Besides confirming the association of HLA-DR3 with GD, this study also suggests the role of Coxsackie-reactive HLA-DR3 antibodies as contributing factors to the pathogenesis of the disease.

MHC class I and II expression in prostate carcinoma and modulation by interferon-alpha and -gamma

BACKGROUND

Expression of Major Histocompatibility Complex (MHC) class I and II antigens are critical for the cellular immune response. Loss of MHC expression represents one mechanism by which cancer cells escape immune recognition.

PURPOSE

To define MHC class I and II expression by prostate cancer (PCa) in vivo and in vitro and the ability to modulate MHC expression in vitro with IFN-alpha and -gamma.

METHODS

Frozen tissue sections of 25 benign prostatic hyperplasia (BPH) and 18 PCa specimens were studied by immunohistochemistry. PCa cell lines LNCaP, PC-3, and DU-145 were studied by FACS, ELISA, and cytospin. Class I was detected by monoclonal antibody (mAb) W6/32, and class II by mAb 13.17. The effects of IFN-alpha and -gamma were assessed by testing the three cell lines in the presence or absence of varying concentrations of the cytokine for varying incubation times.

RESULTS

Class I was strongly expressed by 24/25 BPH specimens; 4/18 (22%) PCa were homogeneously class I-positive, while 5/18 (28%) were heterogeneously positive and 9/18 (50%) were class I-negative. PC-3 and DU-145 expressed normal levels of class I, while LNCaP expressed only low levels. All line except LNCaP demonstrated significant up-regulation of class I with either IFN-alpha or -gamma. Class II expression was not seen in BPH epithelium nor in 17/18 PCa. Class II could be only weakly induced in the three PCa lines.

CONCLUSIONS

These findings confirm prior studies demonstrating that class I expression is commonly lost or diminished in PCa. In addition, class II up-regulation by IFN-gamma appears very limited in relation to other normal or neoplastic epithelium.

IMPLICATIONS

The present findings, taken together with previous studies, are most consistent with the expression of neoantigens by PCa, which are recognized and appropriately eliminated by the cellular immune system. This selective pressure favors outgrowth of cells which down-regulate or lose class I and/or class II expression. Understanding PCa immunobiology will help in the development of effective immunotherapy for this disease.

What is required of an HIV vaccine?

Mounting evidence suggests that the early dissemination of HIV in human beings evokes an immune response that is responsible for containment of the infection during the long symptom-free period. Loss of this immune control coincides with a final escalation of the viraemia and the terminal failure of the immune system. Other studies imply that pre-emptive vaccination of monkeys with attenuated forms of simian immunodeficiency virus (SIV) produces a substantial degree of resistance to superinfection with fully virulent viruses. Here we consider how observations from natural and experimental systems might influence thought as to what is required to produce safe induced immunity against HIV. We concentrate on three questions: what is the nature of the immune response that contains the infection? How does this response fail? How could a vaccine enhance protective immunity so that it exceeds the efficacy of this natural response?

How many thymocytes audition for selection?

T cell maturation requires the rearrangement of clonotypic T cell receptors (TCR) capable of interacting with major histocompatibility complex (MHC) ligands to initiate positive and negative selection. Only 3-5% of thymocytes mature to join the peripheral T cell pool. To investigate the basis for this low success rate, we have measured the frequency of preselection thymocytes capable of responding to MHC. As many as one in five MHC-naive thymocytes show upregulation of activation markers on exposure to MHC-expressing thymic stroma in short-term reaggregate culture. The majority of these cells display physiological changes consistent with entry into the selection process within 24 h. By exposing TCR transgenic thymocytes to a range of MHC-peptide complexes, we show that CD69 induction is indicative of thymocyte selection, positive or negative. Our data provide evidence that the fraction of thymocytes that qualify to enter the thymic selection process far exceeds the fraction that successfully complete it, and suggest that most MHC-reactive thymocytes are actively eliminated in the course of selection.

Neonatal DNA immunization with a plasmid encoding an internal viral protein is effective in the presence of maternal antibodies and protects against subsequent viral challenge

Conventional vaccines are remarkably effective in adults but are much less successful in the very young, who are less able to initiate a mature immune response and who may carry maternal antibodies which inactivate standard vaccines. We set out to determine whether DNA immunization might circumvent these problems. We have previously shown that intramuscular injection of plasmid DNA encoding the nucleoprotein (NP) gene of lymphocytic choriomeningitis virus (LCMV) is capable of inducing immune responses and protecting 50% of adult mice against lethal and sublethal challenge with LCMV. Here we demonstrate that mouse pups injected with the same plasmid hours or days after birth produce major histocompatibility complex-restricted, NP-specific cytotoxic T lymphocytes (CTL) that persist into adulthood; 48% of vaccinated pups responded to subsequent sublethal viral challenge by the accelerated production of anti-NP LCMV-specific CTL, indicating that these animals had been successfully immunized by the plasmid DNA. In addition, these mice showed a >95% reduction in splenic viral titers 4 days postinfection compared to control mice, demonstrating a more rapid control of infection in vivo. Furthermore, pups born of and suckled on LCMV-immune dams (and therefore containing passively acquired anti-LCMV antibodies at the time of DNA inoculation) responded to the DNA vaccine in a similar manner, showing that maternally derived anti-LCMV antibodies do not significantly inhibit the generation of protective immune responses following DNA vaccination. These findings suggest that, at least in this model system, DNA immunization circumvents many of the problems associated with neonatal immunization.

Induction of vigorous cytotoxic T-lymphocyte responses by live attenuated simian immunodeficiency virus

Although live attenuated vaccine strains of simian immunodeficiency virus (SIV) have proven highly effective in protecting macaques against challenge with pathogenic SIV strains, little is known about the mechanisms of protective immunity induced by these vaccines. We examined cytotoxic T-lymphocyte (CTL) responses against SIV in animals infected with SIVmac239delta nef (deficient in nef) or SIVmac239delta 3 (deficient in nef, vpr, and upstream sequences in U3). To enhance detection of SIV-specific CTL activity, we stimulated peripheral blood mononuclear cells with autologous B-lymphoblastoid cell lines which had been infected with recombinant vaccinia viruses expressing SIV proteins and subsequently inactivated with psoralen and UV light. Animals chronically infected with SIV239delta nef or SIV239delta 3 mounted vigorous CTL responses against the SIV Gag and Env proteins. This CTL activity was major histocompatibility class restricted and mediated by CD8+ T lymphocytes. CTL responses persisted at relatively high levels for more than 6 years after infection. Limiting dilution precursor frequency assays demonstrated that the frequency of SIV-specific CTLs was as high as 234 CTL precursors per 100,000 cells. Animals acutely infected with SIV239delta nef developed CTL activity by day 14 after infection, coincident with decreases in viral load. Animals acutely infected with SIV239delta 3 developed CTL responses within 4 weeks of infection. Thus, vaccination of juvenile or adult animals with SIV239delta nef or SIV239delta 3 results in the induction of a vigorous CTL response which arises early in the course of infection and persists for years after a single inoculation of virus.

On the mystique of the immunological self

Since the time of Paul Ehrlich 100 years ago, we have known that the immunological apparatus somehow inhibits most damaging autoimmune responses while permitting a response to exogenous immunogens. With the discovery of tolerance, the concept of immunological surveillance, and especially with the discovery of HLA restriction of T-cell recognition, the term "the immunological self" and the phrase "self-nonself discrimination" have gained wide currency. Immunology has been called "The Science of Self", and self-nonself discrimination has been assigned as the driving force for its complex evolution. The concept of self has thus been given such mystical trappings since the time of Macfarlane Burnet that recent workers have felt free to pronounce it the central paradigm of modern immunology, and to claim to overthrow it! In this article, we challenge some of the more egregious claims about the immunological self by recalling important historical findings, by reviewing the mechanisms of Darwinian evolution, and by remembering that the general pathology of immunogenic inflammation shows that the immune response cannot discriminate between the benign and the noxious.

Effector CD4+ and CD8+ T-cell mechanisms in the control of respiratory virus infections

The rules for T-cell-mediated control of viruses that infect via the respiratory mucosae show both common themes and differences, depending on the nature of the pathogen. Virus-specific CD8+ cytotoxic T lymphocytes (CTLs) are the key effectors of virus clearance in mice infected with both negative strand RNA viruses (influenza and Sendai) and a DNA virus, the murine gamma-herpesvirus-68 (MHV-68). Recently completed experiments establish that these activated CD8+ T cells indeed operate primarily via contact-dependent lysis. Perforin-mediated cytotoxicity seems to be the preferred mode, though a Fas-based mechanism can apparently serve as an alternative mechanism. Immune CD4+ T cells functioning in the absence of the CD8+ subset cannot eliminate MHV-68 from lung epithelial cells, are somewhat less efficient than the CD8+ CTLs at clearing the RNA viruses, and are generally ineffectual in mice that lack B lymphocytes. Though cytokine secretion by CD4+ and CD8+ T cells in the virus-infected lung may promote both T-cell extravasation and macrophage activation, such processes are not alone sufficient to deal consistently with any of these infections. However, CD4+ T help is mandatory for an effective B-cell response, and can operate to promote the clonal expansion of virus-specific CD8+ T cells in the lymph nodes and spleen. Furthermore, a concurrent CD4+ T-cell response seems to be essential for maintaining continued CD8+ T-cell surveillance and effector capacity through the persistent, latent phase of MHV-68 infection in B cells. Thus, the evidence to date supports a very traditional view; CD8+ T cells function mainly as killers and the CD4+ T cells as helpers in these respiratory virus infections.

Role of the B-cell response in recovery of mice from primary influenza virus infection

Recovery from influenza virus infection has long been known to require an intact T-cell compartment. More recent studies revealed that CD8 and CD4 T cells can promote recovery through independent mechanisms. The CD4 T-cell-dependent recovery process appears to operate primarily through promotion of the T-dependent antibody response as B-cell-deficient microMT mice cannot recover from infection if they have been depleted of CD8 T cells. The potential therapeutic activity of the B-cell response was further studied by transfer of antibodies into infected SCID mice. At the dose of 200 micrograms/mouse, most antibodies (of IgG2a isotype) to the viral transmembrane protein HA cured the infection, while those to the transmembrane proteins NA and M2 suppressed virus titers in the lung but failed to clear the infection. The ability of passive antibody to resolve the infection was closely related to its prophylactic activity, suggesting that neutralization of progeny virus (VN) played an important role in the process of virus clearance in vivo, while reaction of antibodies with infected host cells contributed to but was insufficient, on its own, for cure. HA-specific antibodies of IgM and IgA isotypes were therapeutically ineffective against pulmonary infection, presumably because of a preferential delivery into the upper respiratory tract, while IgG exhibited highest activity against pulmonary and minimal activity against nasal infection. B cells appear to be of similar importance for recovery from primary infection as CD8 T cells.

Bone Marrow Contains Virus-Specific Cytotoxic T Lymphocytes

Immunizing bone marrow donors prior to bone marrow transplant (BMT) has the potential for adoptively transferring specific immunity against opportunistic pathogens. Studies have shown that long-term antibody production occurs in the bone marrow and that specific humoral immunity may be transferred from donor to recipient following BMT. However, the magnitude and duration of T-cell memory in the bone marrow compartment has not been adequately investigated. In this study, virus-specific CD8+ T-cell responses in the bone marrow were compared with those observed in the spleen of mice acutely infected with lymphocytic choriomeningitis virus (LCMV). During the acute stages of infection, most CD8+ T cells in the spleen and bone marrow showed upregulated surface expression of the activation/memory marker, LFA-1 (LFA-1hi). After clearing LCMV infection, the antiviral immune response subsided to homeostatic levels and the ratio of CD8+/LFA-1hi to CD8+/LFA-1lo T cells in the spleen and bone marrow of LCMV immune mice returned to the value observed in naive mice. Virus-specific ex vivo effector cytotoxic T-lymphocyte (CTL) responses could be identified in both spleen and bone marrow compartments at 8 days postinfection. LCMV-specific CTL precursor (CTLp) frequencies peaked in the bone marrow at 8 days postinfection and averaged one in 200 to one in 650 CD8+ T cells, a frequency similar to that observed in the spleen. After clearing the acute infection, potent LCMV-specific CTL memory responses could be demonstrated in the bone marrow for at least 325 days postinfection, indicating long-term persistence of antiviral T cells at this site. Adoptive transfer of LCMV-immune bone marrow into severe combined immunodeficiency (SCID) mice provided protection against viral challenge, whereas SCID mice that received naive bone marrow became chronically infected upon challenge with LCMV. These results indicate that after acute viral infection, virus-specific memory T cells can be found in the bone marrow compartment and are maintained for an extended period, and when adoptively transferred into an immunodeficient host, they are capable of conferring protection against chronic viral infection.

Recombinant Listeria monocytogenes as a live vaccine vehicle and a probe for studying cell-mediated immunity

The ability of Listeria monocytogenes (L. monocytogenes) to enter the cytosol of host cells allows secreted proteins to efficiently enter the endogenous antigen-processing pathway leading to presentation by MHC class I molecules. L. monocytogenes has recently been exploited as a live vaccine vehicle for the induction of immunological memory against heterologous antigens. We have established a genetic system for site-specific integration of antigen expression cassettes into the Listeria genome which allows regulated expression and secretion of heterologous proteins. The ability of recombinant strains to stimulate long-term immunological memory and CD8+ T-cell-mediated protective immunity was investigated using the lymphocytic choriomeningitis virus (LCMV) murine infection model. Vaccination of mice with recombinant Listeria strains expressing LCMV antigens induced LCMV-specific CD8+ T cells which protected mice against LCMV challenge. We have also used a cottontail rabbit papillomavirus model to test the ability of recombinant Listeria strains to stimulate protective antitumor immunity in domestic rabbits. These studies have demonstrated the protective efficacy of recombinant L. monocytogenes vaccines and have established an experimental system for systematic analysis of cytotoxic T-cell induction by an intracellular bacterium.

Interferon-gamma rapidly increases peptide transporter (TAP) subunit expression and peptide transport capacity in endothelial cells

Human cytotoxic T lymphocytes (CTL) recognize specific complexes of HLA class I molecules and peptides, which assemble when nascent class I molecules bind peptides transported from the cytoplasm into the endoplasmic reticulum by the heterodimeric transporter associated with antigen processing (TAP). Increased class I molecule expression on the cell surface increases the efficiency of CTL lysis. The kinetics of interferon (IFN)-gamma induction of TAP, peptide transport capacity, and HLA class I molecule expression was determined in endothelial cells, which are targets of CTL following transplantation or viral infection. TAP mRNAs are induced rapidly, increasing 20-fold (TAP1) or 10-fold (TAP2) by 12 h, whereas HLA class I mRNA is induced more slowly, increasing 10-fold in 24 h. TAP1 and TAP2 proteins are also induced rapidly, increasing 10-fold in 24 h, whereas HLA class I heavy chain proteins and surface expression increase more slowly. Peptide transport capacity in endothelial and HeLa cells increases within 6 h of IFN-gamma treatment, suggesting that the IFN-gamma-induced TAP heterodimers are functional. Therefore, the IFN-gamma-induced increase in TAP proteins is accompanied by an increased peptide transport capacity, which may be important in supporting the subsequent rise in HLA class I protein expression.

Hypothesis: MHC class I, rather than just a flagpole for CD8+ T cells is also a protease in its own right

Ever since the discovery of MHC class I restriction and the onslaught of the dual receptor hypothesis, MHC class I has been perceived as a passive entity in TCR recognition and the appropriate antigen processing and presentation pathways. However, numerous experimental observations and theoretical considerations are difficult or unable to be explained by the accepted mechanism of class I antigen presentation. Proteases within and outside the endoplasmic reticulum (ER) are evoked to be solely responsible for the generation of the appropriate 8-10 amino acid-long peptides associated with MHC class I. A MHC class I with site-restricted ER protease activity would overcome most of the present difficulties in explaining MHC class I antigen presentation.

Assignment of the human gene for KBF2/RBP-Jk to chromosome 9p12-13 and 9q13 by fluorescence in situ hybridization

The transcription factor KBF2 has been characterized as a factor that binds to the NFkB site of mouse major histocompatibility complex (MHC) class I genes and its amino acid sequence has been shwn to be identical to those of members of the recombination signal-sequence binding protein (RBP-Jk) family. Previous studies by Amakawa et al. (Genomics 17, 306-315, 1993) demonstrated that the functional gene is localized at human chromosome 3q25. However, in the present study we showed by in situ hybridization with the functional KBF2/RBPJk cosmid clone that the gene is localized at 9p12-13 and 9q13, namely, at the same loci as pseudogenes that were reported previously (Zhang et al, Jpn J Human Genet 39, 391-401, 1994).

Analyzing cytotoxic T lymphocyte activity: a simple and reliable flow cytometry-based assay

A flow cytometry-based assay for analyzing cytotoxic T lymphocyte (CTL) activity is presented. This new approach is characterized by easy handling, the generation of highly reproducible data sets and is not dependent on the use of radioactivity. Before exposure to primed CTL effector cells the target cells were labeled with the green fluorescent dye DiO18(3) which is incorporated stably into the cell membrane. After a 4-h incubation period, samples were counterstained with the red fluorescent nuclear dye propidium iodide in order to permit discrimination between live and dead cells within both cell populations. The assay has been used to quantitate CTL effector activity against allogeneic lymphoblasts. Results derived from this novel flow cytometry assay show an excellent correlation (r = 0.988) with data obtained using the standard 51chromium release assay. An additional advantage of the assay is that freshly prepared splenocytes may be used as target cells because culturing and activation of target cells is no longer required. The results demonstrate that the fluorescent dyes DiO18(3) and propidium iodide in combination with flow cytometry permit accurate analysis of cytotoxic T cell activity.

Measurement of relative quantities of different HLA-A and -B mRNAs in cells by reverse transcription-polymerase chain reaction and denaturing gradient gel electrophoresis

In order to determine the relative quantities of different HLA-A and -B mRNAs in cells, we have developed a simple and reliable method by using reverse transcription-polymerase chain reaction (RT-PCR), denaturing gradient gel electrophoresis (DGGE) and phosphor imaging analysis. Cytoplasmic RNA from lymphoblastoid cell lines with well-characterized HLA phenotypes are reversely transcribed with a primer specific for all HLA-A and -B antigens. The first-strand cDNA is used as template for quantitative PCR. The primer pair used for quantitative PCR are specific for all class I HLA and one of the primers is labeled with [gamma-32P]ATP. The amplified sequences include parts of exon 2 and exon 3 which contain most polymorphic residues in class I HLA molecules. The RT-PCR products containing the amplified HLA-A and -B sequences are separated by DGGE. The radioactivities of different DNA bands separated in denaturing gradient polyacrylamide gels are measured by phosphor imaging and used to determine the relative amounts of HLA-A and -B mRNAs. This approach is validated by using samples containing known quantities of different HLA-A and -B mRNA transcripts and confirmed by S1 nuclease protection assay. The combined RT-PCR/DGGE approach therefore provides a simple and reliable method for quantitation of relative amounts of different HLA-A and -B mRNAs in cells. This method should also be useful for studying the expression of other highly conserved and duplicated genes.

Protective cellular immunity: cytotoxic T-lymphocyte responses against dominant and recessive epitopes of influenza virus nucleoprotein induced by DNA immunization

DNA immunization offers a novel means to induce cellular immunity in a population with a heterogeneous genetic background. An immunorecessive cytotoxic T-lymphocyte (CTL) epitope in influenza virus nucleoprotein (NP), residues 218 to 226, was identified when mice were immunized with a plasmid DNA encoding a full-length mutant NP in which the anchor residues for the immunodominant NP147-155 epitope were altered. Mice immunized with wild-type or mutant NP DNA were protected from lethal cross-strain virus challenge, and the protection could be adoptively transferred by immune splenocytes, indicating the role of cell-mediated immunity in the protection. DNA immunization is capable of eliciting protective cellular immunity against both immunodominant and immunorecessive CTL epitopes in the hierarchy seen with virus infection.

Various functions of PBMC from colon cancer patients are not decreased compared to healthy blood donors

The immune surveillance hypothesis suggests impaired immune responses to participate in development of cancer. This may partly be due to increased amounts of PGE2 and histamine, which inhibit cellular immunity. These effects are mediated by cAMP, which is increased and thereby may down-regulate IL-2 and its receptor proteins in T helper cells. The proliferative responses and IL-2 synthesis of PBMC have earlier been shown to be reduced in patients with colon cancer. Recently immune modulating agents have been demonstrated to increase the proliferative response of PBMC in vitro, probably by inhibition of adenylate cyclase activity and induction of IL-2 mRNA expression. We have therefore studied the proliferative responses of PBMC from colon cancer patients to PWM and tested the effect of immune modulating agents, such as Serotonin, Sumatriptan, and Buspirone on these PBMC. We found no difference in levels of intracellular cAMP, IL-2 mRNA expression, IL-2R mRNA expression, or proliferative responses of PBMC from colon cancer patients compared to healthy blood donors. There was no effect of the immune modulating agents on PBMC from colon cancer patients.

Traffic control of completely assembled MHC class I molecules beyond the endoplasmic reticulum

It is generally assumed that MHC class I molecules arrive at the plasma membrane following biosynthesis, assembly and architectural editing in the endoplasmic reticulum by constitutive forward movement without requirement for specific signals (bulk flow). If this is true then all overexpressed completely assembled class I molecules should arrive at the cell surface. To study the itinerary of class I traffic beyond the endoplasmic reticulum, mammalian cells that overexpress 20 to 50-fold higher amounts of the constituent heavy and light chains were established. Thorough biochemical analyses revealed that such overexpressed molecules assemble with authentic peptides that contain the canonical class I binding anchor motif in almost 1:1 stoichiometry and impart thermal stability to the heterotrimeric complex. Despite complete assembly, however, only a fraction of the overexpressed molecules reaches the cell surface. Almost all of the overexpressed class I molecules are sialylated, thus traffic as far as the trans-Golgi or the trans-Golgi network. Overexpression of class I molecules do not seem to cause a "traffic jam" in the exocytic pathway because the kinetics of traffic of Sindbis virus structural proteins to the plasma membrane are almost identical when comparing the non-engineered and engineered cells. Thus the steady state expression of class I molecules at the cell surface is further controlled either in the Golgi apparatus or at the plasma membrane.

Interferon-gamma enhances resolution of herpes simplex virus type 2 infection of the murine genital tract

The requirement for interferon-gamma (IFN gamma) in resolution of an HSV-2 vaginal infection and the cellular sources of this cytokine in the vaginal mucosa were assessed. IFN gamma levels in vaginal secretions peaked on Days 2 and 5 following HSV-2 inoculation. Natural killer (NK) cell depletion greatly diminished the early production of IFN gamma but had no significant effect on the rate of virus clearance. CD4+ T cells were primarily responsible for the second peak of IFN gamma levels and neutralization of this IFN gamma beginning 3 days after virus inoculation delayed, but did not prevent, virus clearance from the vagina. HSV-2 persisted in mice depleted of both CD4+ and CD8+ T cells while clearance was delayed in CD4+, but not CD8+ T cell-depleted mice, demonstrating the T cell dependence and predominant role of CD4+ T cells in resolution of the infection. Together, these data suggest that IFN gamma is not essential for virus clearance but plays an important role in enhancing T cell-mediated clearance mechanisms. The implication of these results is that IFN gamma produced locally in the genital tract enhances virus clearance and may ultimately be important for reducing the amount of virus available to infect sensory ganglia.

Viruses use stealth technology to escape from the host immune system

In this review, we focus on recent investigations that reveal novel mechanisms by which viruses evade detection and elimination by the host immune system. In particular, we consider the evasion mechanisms of five persistent viruses: herpes simplex virus, human cytomegalovirus, mouse cytomegalovirus, Epstein-Barr virus and adenovirus. Unravelling the strategies used by viruses to survive within the host could identify new targets for antiviral drugs and for improved vaccines. Identification of the mechanisms that underlie these strategies might also reveal new, fundamental features of biology that occur in uninfected cells and are exploited by viruses.

Comparison of cytotoxic T lymphocyte responses induced by peptide or DNA immunization: implications on immunogenicity and immunodominance

To study the mechanisms that influence the immunogenicity and immunodominance of potential cytotoxic T lymphocyte (CTL) epitopes, we conducted a systematic analysis of the CTL response raised in HLA-A*0201/Kb (A2/Kb) transgenic mice against the viral antigen, hepatitis B virus polymerase (HBV pol). From a pool of 26 nonamer peptides containing the HLA-A*0201-binding motif, we selected A2-binding peptides, immunized A2/Kb animals, and tested the CTL raised against the peptide for recognition of HBV pol transfectants. Of nine immunogenic CTL epitopes, only four were recognized on HBV pol transfectants, whereas the other five were cryptic. Characterization of the peptide-specific CTL lines indicated that crypticity may result from either poor processing or low T cell receptor (TCR) avidity. To identify the immunodominant epitopes, we determined the CTL specificities induced in A2/Kb animals in response to priming with HBV pol cDNA. We obtained a response against three epitopes that were contained with the set of four epitopes recognized by peptide-specific CTL on HBV pol transfectants. Comparative analysis of cDNA priming and peptide priming revealed, therefore, the presence of a subdominant epitope. We conclude that for the HBV pol antigen, the repertoire of CTL specificities is shaped by major histocompatibility complex class I peptide binding capacity, antigen processing, and TCR availability.