The human cathepsin H gene encodes two novel minor histocompatibility antigen epitopes restricted by HLA-A*3101 and -A*3303

Minor histocompatibility antigens (mHags) play crucial roles in the induction of graft versus host disease (GVHD) and/or graft versus leukaemia (GVL) effects following human leucocyte antigen (HLA)-identical haematopoietic stem cell transplantation (HSCT). Using HLA-A*3101- and -A*3303-restricted cytotoxic T lymphocyte (CTL) clones generated from different post-HSCT recipients, we identified two novel mHag epitopes encoded by the leader sequence of cathepsin H (CTSH) isoform a. The nonameric sequence ATLPLLCAR was defined as an HLA-A*3101-restricted epitope (CTSH(R)/A31), while a decameric peptide featuring a one N-terminal amino acid extension, WATLPLLCAR, was presented by HLA-A*3303 (CTSH(R)/A33). The immunogenicity of both epitopes was totally dependent on the polymorphic C-terminal arginine residue and substitution with glycine completely abolished binding to the corresponding HLA molecules. Thus, the immunogenicity of this mHag is exerted by differential HLA binding capacity. CTSH is relatively ubiquitously expressed at protein levels, thus it may be involved in GVHD and anti-leukaemic/tumour responses. Interestingly, however, CTL clones predominantly lysed targets of haematopoietic cell origin, which could not be explained in terms of the immunoproteasome system. Although the mechanisms involved in the differential susceptibility remain to be determined, these data suggest that CTSH-encoded mHags could be targets for GVL effects.

Identification of HLA class II-restricted H-Y-specific T-helper epitope evoking CD4+ T-helper cells in H-Y-mismatched transplantation

BACKGROUND

Stem-cell grafts between HLA-identical siblings are less likely to succeed when there is a sex mismatch. This lack of success can be interpreted as enhanced activity directed against minor histocompatibility antigens encoded by the Y chromosome (H-Y). So far, in man, only cytotoxic T lymphocytes (CTLs) specific for several minor histocompatibility antigens have been reported. We aimed to identify and clarify the role of MHC class II-restricted H-Y-specific T-helper cells in these transplant settings.

METHODS

H-Y-specific MHC class II-restricted CD4+ T cells were isolated from blood of a female patient who rejected an HLA-identical male stem-cell transplant. By molecular cloning of H-Y genes and functional T-helper experiments, we elucidated antigen specificity and the functional properties of these H-Y-specific T-helper cells.

FINDINGS

CD4+ T-helper cells recognise the Y gene-encoded peptide VIKVNDTVQI presented by HLA-DRbeta3*0301. These T-helper cells mature dendritic cells and enhance expansion of minor histocompatibility antigen-specific MHC class I-restricted CD8+ CTLs.

INTERPRETATION

Characterisation of an MHC class II-restricted H-Y epitope that evoked CD4+ T-helper responses adds a novel cellular component to the alloimmune response against Y chromosome-encoded minor histocompatibility antigens. This component completes the H-Y-directed alloimmune response and aids understanding of the poorer outcome of sex-mismatched transplants.

Immunodominance of H60 is caused by an abnormally high precursor T cell pool directed against its unique minor histocompatibility antigen peptide

The H60 minor histocompatibility (H) antigen peptide is derived from a glycoprotein that serves as a ligand for the stimulatory NKG2D receptor. We show that this peptide is remarkably immunodominant in that it competes effectively with MHC alloantigens, is efficiently crosspresented by host antigen-presenting cells (APCs), and readily elicits naive CD8 T cell responses in vitro. H60 immunodominance is neither a consequence of NKG2D engagement nor competition among minor H antigens on APCs. Instead, H60 immunodominance is a consequence of an abnormally high naive precursor frequency of H60 peptide reactive CD8 T cells. Understanding why the H60 peptide is so immunogenic has important implications in tissue transplantation and vaccine design.

CD40 ligand blockade induces CD4+ T cell tolerance and linked suppression

The CD40-CD40 ligand (CD40L) interaction is a key event in the initiation of an adaptive immune response, and as such the therapeutic value of CD40L blockade has been studied in many experimental models of tissue transplantation and autoimmune disease. In rodents, transplantation of allogeneic tissues under the cover of anti-CD40L Abs has resulted in prolonged graft survival but not tolerance. In this report, we show that failure to induce tolerance probably results from the inability of anti-CD40L Abs to prevent graft rejection elicited by the CD8+ T cell subset. When the CD8+ T cell population is controlled independently, using anti-CD8 Abs, then tolerance is possible. Transplantation tolerance induced by anti-CD4 mAbs can often be associated with dominant regulation, manifested as infectious tolerance and linked suppression, both of which are mediated by CD4+ T cells. We show here that CD4+ T cells rendered tolerant using anti-CD40L therapy exhibit the same regulatory property of linked suppression, as demonstrated by their ability to accept grafts expressing third party Ags only if they are expressed in conjunction with the tolerated Ags. This observation of linked suppression reveals a hitherto undocumented consequence of CD40L blockade that suggests the tolerant state is maintained by a dominant regulatory mechanism. Our results suggest that, although anti-CD40L Abs are attractive clinical immunotherapeutic agents, additional therapies to control aggressive CD8+ T cell responses may be required.

Polyriboinosinic polyribocytidylic acid (poly(I:C)) induces stable maturation of functionally active human dendritic cells

For vaccination strategies and adoptive immunotherapy purposes, immature dendritic cells (DC) can be generated from adherent monocytes using GM-CSF and IL-4. Presently, the only clinically applicable method to induce stable maturation of DC is the use of supernatants of activated monocytes (monocyte-conditioned medium (MCM)). MCM contains an undefined mixture of cytokines and is difficult to standardize. Here we report that stable maturation of DC can be simply induced by the addition of polyriboinosinic polyribocytidylic acid (poly(I:C)), a synthetic dsRNA clinically applied as an immunomodulator. Poly(I:C)-treated DC show a mature phenotype with high expression levels of HLA-DR, CD86, and the DC maturation marker CD83. This mature phenotype is retained for 48 h after cytokine withdrawal. In contrast to untreated DC, poly(I:C)-treated DC down-regulate pinocytosis, produce high levels of IL-12 and low levels of IL-10, induce strong T cell proliferation in a primary allo MLR, and effectively present peptide Ags to HLA class I-restricted CTL. In conclusion, we present a simple methodology for the preparation of clinically applicable mature DC.

Biochemical and immunogenetic analysis of an immunodominant peptide (B6dom1) encoded by the classical H7 minor histocompatibility locus

Of the many minor histocompatibility (H) Ags that have been detected in mice, the ability to induce graft vs host disease (GVHD) after bone marrow transplantation is restricted to a limited number of immunodominant Ags. One such murine Ag, B6dom1, is presented by the H2-Db MHC class I molecule. We present biochemical evidence that the natural B6dom1 peptide is indistinguishable from AAPDNRETF, and we show that this peptide can be isolated from a wide array of tissues, with highest levels from the lymphoid organs and lung. Moreover, we employ a novel, somatic cell selection technique involving CTL-mediated immunoselection coupled with classical genetics, to show that B6dom1 is encoded by the H7 minor H locus originally discovered approximately 40 years ago. These studies provide a molecular genetic framework for understanding B6dom1, and exemplify the fact that mouse minor H loci that encode immunodominant CTL epitopes can correspond to classical H loci originally identified by their ability to confer strong resistance to tumor transplantation. Additionally, these studies demonstrate the utility of somatic cell selection approaches toward resolving H Ag immunogenetics.

Contributions of direct and indirect T cell alloreactivity during allograft rejection in mice

The immune response to transplanted allogeneic tissues is mediated by T cells that recognize donor histocompatibility Ags either via direct (donor MHC and peptides) or indirect (recipient MHC and donor-derived peptides) allorecognition pathways. The relative contribution of each of these pathways to allograft rejection remains largely unknown. To address this, we used an enzyme-linked immunospot assay to define the frequency and cytokine phenotype of T cells responding via direct and indirect pathways to alloantigens at various time points following placement of allogeneic B10.A skin grafts on BALB/c recipient mice. During acute graft rejection >90% of the anti-B10.A T cell repertoire was directed toward intact donor MHC molecules, while T cells recognizing indirectly presented, donor-derived peptides accounted for <10%. This indirect response was comprised of reactivity toward both MHC-derived and, to a lesser extent, minor Ag-derived determinants. The direct and indirect alloresponses were predominantly detected in recipient lymph nodes and were mediated by T cells displaying a mixed type 1/type 2 cytokine phenotype. Six weeks following rejection, however, the memory allospecific T cell response became predominant in the recipient spleen, with only minimal activity detectable in the draining lymph nodes. This work provides a new approach for analysis of the immunophysiology of allograft rejection and should be useful for monitoring immune responses to graft Ags in human transplant recipients.

Linked suppression of skin graft rejection can operate through indirect recognition

Adult mice can be rendered immunologically tolerant of allogeneic tissues if transplanted under cover of mAbs to CD4 and CD8. Tolerance generated in this manner is characterized by the presence of regulatory CD4+ T cells that can recruit naive T cells to become tolerant also through "infectious tolerance." Regulatory CD4+ T cells can also suppress rejection of third party transplant Ags provided they are expressed on the same graft as the tolerated Ags. This process of linked suppression can act across whole MHC barriers and represents a powerful mechanism with therapeutic potential. Tolerance can also be induced to reprocessed minor transplantation Ags presented through host APCs (indirect recognition). We here demonstrate that linked suppression can also be induced through the indirect pathway. This finding may be important in the development of transplantation tolerance in the clinic.

Expression screening of a yeast artificial chromosome contig refines the location of the mouse H3a minor histocompatibility antigen gene

The H3 complex, on mouse Chromosome 2, is an important model locus for understanding mechanisms underlying non-self Ag recognition during tissue transplantation rejection between MHC-matched mouse strains. H3a is a minor histocompatibility Ag gene, located within H3, that encodes a polymorphic peptide alloantigen recognized by cytolytic T cells. Other genes within the complex include beta2-microglobulin and H3b. A yeast artificial chromosome (YAC) contig is described that spans the interval between D2Mit444 and D2Mit17, a region known to contain H3a. This contig refines the position of many genes and anonymous loci. In addition, 23 new sequence-tagged sites are described that further increase the genetic resolution surrounding H3a. A novel assay was developed to determine the location of H3a within the contig. Representative YACs were modified by retrofitting with a mammalian selectable marker, and then introduced by spheroplast fusion into mouse L cells. YAC-containing L cells were screened for the expression of the YAC-encoded H3a(a) Ag by using them as targets in a cell-mediated lympholysis assay with H3a(a)-specific CTLs. A single YAC carrying H3a was identified. Based on the location of this YAC within the contig, many candidate genes can be eliminated. The data position H3a between Tyro3 and Epb4.2, in close proximity to Capn3. These studies illustrate how genetic and genomic information can be exploited toward identifying genes encoding not only histocompatibility Ags, but also any autoantigen recognized by T cells.

Influences of transporter associated with antigen processing (TAP) on the repertoire of peptides associated with the endoplasmic reticulum-resident stress protein gp96

The endoplasmic reticulum (ER)-resident stress protein gp96 induces protective immunity and specific cytotoxic T lymphocyte (CTL) responses against antigens expressed in those cells it has been isolated from. This ability is based on peptides associated with gp96. Because gp96 is located inside the ER, our experiments address the question whether or not the repertoire of peptides associated with gp96 is influenced by the transporter associated with antigen processing (TAP). For this purpose, gp96 was isolated from cells with and without a TAP defect and used for immunization of mice. We found that for some antigens the association of peptides with gp96 required functional TAP molecules, whereas the association of peptides from other antigens was TAP independent. In the case of a TAP-dependent association of peptides with gp96, our results prove that peptide binding by gp96 in vivo occurs inside the ER and is not an artifact induced by cell lysis during the gp96 purification. The finding that some antigens can also associate with gp96 in the absence of functional TAP molecules indicates that the repertoire of peptides bound by gp96 truly reflects the entire repertoire of peptides present inside the ER and not only those peptides transported by TAP. These results, together with the earlier finding that the gp96 peptide repertoire is independent of the major histocompatibility complex molecules expressed by the cell gp96 is isolated from, give the theoretical foundation for the ability of gp96 to induce CTL responses against all kinds of intracellular antigens.

Lack of GVHD across classical, single minor histocompatibiliTy (miH) locus barriers in mice

To determine whether a disparity at a single miH genetic loci are sufficient to generate GVHD in mice, we focused on well-known genetic alleleic differences at the miH gene loci, H3 and H4. For H3 congenic GVHD studies, C57BL/10 (H2b) mice were used as recipients of miH-disparate B10.LP-H3b donor cells. For H4 congenic GVHD studies, C57BL/10 were used as recipients for miH-disparate B10.129 (21M)-H4b. To overcome the low frequency of miH-reactive CTLs in naive mice, multiple immunizations of the donor strains with host lymphohematopoietic cells were used. Peripheral blood cells from immunized mice were shown to have potent CTL activity against their respective host-type stimulator cells when analyzed 1 week prior to obtaining donor splenocytes for GVHD induction. Lethally irradiated C57BL/6 recipients of either 50 X 10(6) donor B10.LP-H3b or B10.129 (21M)-H4b splenocytes did not develop acute or chronic GVHD as assessed by monitoring the animals for survival, weight loss, splenic flow cytometry, and histological examination of skin, liver, colon, and lung in long-term survivors. Engraftment was documented in long-term chimeras in both strain combinations by using the post-BMT cells as alloantigen targets for cloned CTL lines specific for donor and not host-type miH antigens (H3b or H4b). On day 6 post-BMT, donor antihost CTL activity could not be detected in the spleen, although third-party responses were intact. These results suggest a rapid downregulation or disappearance of miH antigen-reactive CTL after BMT. These data have implications for the use of in vitro assays to predict GVHD risk in recipients of miH loci-disparate donor grafts.

Dissociation of mouse cardiac transplant rejection and donor alloantigen-specific T cell responsiveness

Mouse hearts transplanted into MHC disparate donors are usually rejected 1 week after placement. It is widely accepted that alloantigen-reactive helper T lymphocytes (HTL) and cytotoxic T lymphocytes (CTL) are the key mediators of acute allograft rejection. This report demonstrates that the presence or absence of 'traditional' graft-reactive HTL and CTL is not necessarily related to allograft survival. In these studies, donor/recipient combinations disparate only at MHC or only at minor histocompatibility (mH) loci were employed. Allograft survival was monitored, donor-reactive IL-2 (interleukin-2) producing HTL and CTL were quantified by modified limiting dilution analysis, and serum levels of cytolytic alloantibody were determined. C57BL/10 hearts (H-2b) transplanted into B10.BR (H-2k) recipients (full MHC disparity) enjoyed prolonged survival despite massive infiltration of the allograft by donor-reactive HTL and CTL. IgM, but not IgG, donor-reactive alloantibody was present in the sera of these mice. Hence, traditional IL-2 producing HTL and CTL were not capable of mediating acute graft rejection, nor of providing help for alloantibody isotype switching in this MHC disparate combination. In contrast, C3H/HeN (H-2k) hearts transplanted into B10.BR (H-2k) recipients (mH disparity only) were acutely rejected. Donor-reactive HTL and CTL were rare or not detectable in these recipients, and cytolytic alloantibody was not detectable. Similar observations were made when B10.BR hearts were transplanted into C3H/HeN recipients. Interestingly, treatment of recipients with anti-CD4 monoclonal antibody prevented rejection of mH disparate allografts. Therefore, CD4+ T cells were required for rejection of mH disparate allografts, but this process was independent of detectable IL-2 production or CTL function. Hence, the significance of monitoring 'traditional' T cell functions should be questioned in certain donor/recipient combinations.

Alloantigens introduced into the anterior chamber of the eye induce systemic suppression of delayed hypersensitivity to third-party alloantigens through "linked recognition"

It has been recognized for over a century that the anterior chamber of the eye is endowed with unique immunological properties that permit the long-term survival of histoincompatible grafts that would otherwise be rejected at extraocular sites. Immune privilege in the anterior chamber of the eye has been attributed, at least in part, to the active down regulation of systemic delayed-type hypersensitivity (DTH) that is induced when antigens are introduced into this ocular compartment. The antigen-specific suppression of systemic DTH that is induced by anterior chamber priming has been termed anterior chamber-associated immune deviation (ACAID) and has been demonstrated with a variety of antigens. The present report summarizes a systematic evaluation of various categories of histocompatibility antigens for their capacity to induce ACAID. The results indicate that ACAID can be induced against a wide variety of alloantigens ranging from a single minor histocompatibility antigen (H-Y) to mismatches involving the entire major histocompatibility complex plus multiple minor histocompatibility loci. Further investigation revealed that it was possible to induce suppression of DTH to third-party alloantigens providing the alloantigens introduced into the anterior chamber were coexpressed with the third-party alloantigens on cells used for extraocular immunizations.

Graft-host tolerance in bone marrow transplant chimeras. Absence of graft-versus-host disease is associated with unresponsiveness to minor histocompatibility antigens expressed by all tissues

Because bone marrow (BM) transplantation is used with increasing frequency, it is important to elucidate the mechanisms involved in the establishment of tolerance to host minor histocompatibility antigens (MiHA) in recipients transplanted with T-cell-undepleted marrow grafts. We have previously shown that BM chimeras transplanted across MiHA barriers showed specific unresponsiveness to MiHA expressed on recipient-type concanavalin A blasts. Because expression of many MiHA is tissue-specific, we wanted to determine if chimera T lymphocytes would be tolerant to MiHA expressed by all host tissues and organs. To investigate this issue, we measured in vivo proliferation of lymphoid cells from normal C57BL/10 (B10) mice and (B10-->LP) chimeras in tissues and organs of lethally irradiated syngeneic and allogeneic recipients. Donor B10 cells were either untreated, or depleted with anti-Thy-1.2, anti-CD4, or anti-CD8 antibodies. Transplantation of B10 cells in LP recipients triggered an important T-cell-dependent 125I-dUrd uptake in several organs that involved both CD4+ and CD8+ cells. Using Thy-1-congeneic mice we showed that in long-term chimeras practically all CD4+ and CD8+ T lymphocytes were derived from hematopoietic progenitors and not from mature T cells present in the BM graft. When (B10-->LP) BM chimera cells were injected to secondary recipients, no proliferation was observed in any organ of LP hosts whereas normal proliferation was seen in H-2k allogeneic hosts. Thus, in these BM chimeras, tolerance encompasses MiHA expressed by all organs.

Few peptides dominate cytotoxic T lymphocyte responses to single and multiple minor histocompatibility antigens

Minor histocompatibility (H) antigens are T cell recognized self proteins which can cause graft versus host disease or organ transplant rejection. We have analysed the number of peptide epitopes involved in cytotoxic T lymphocyte (CTL) responses to single or multiple minor H antigens. Bulk CTL responses were generated in H-2b mice differing in one (H-1), two (H-1 and H-25), or multiple (> 29) minor H loci, and HPLC separation was used to analyse the complexity of CTL recognized peptides. Anti-H-1 CTL recognize one out of 50 HPLC peptide fractions and recognition is H-2Kb restricted. The same peptide fraction is also recognized by anti-H-1/H-25 CTL and no additional epitopes are detected, indicating that the H-25 locus does not stimulate CTL when combined with H-1. CTL generated to multiple minor H loci (including H-1 and H-25) recognize two HPLC peptide fractions which are presented by H-2Db and H-2Kb class I molecules, respectively. The H-2Kb presented fraction is the same as that recognized by anti-H-1 and anti-H-1/H-25 CTL, and it is shown to contain a H-1-derived peptide. Subfractionation of the CTL recognized HPLC fractions is consistent with the presence of only one peptide epitope. Thus, in the responses analysed here one minor H locus encodes probably only one CTL epitope. The study provides a molecular explanation for immunodominance among minor H antigens, suggesting that dominant loci encode single peptide epitopes which are presented efficiently by MHC class I molecules enabling them to readily stimulate CTL responses.

Pretransplant detection of human minor histocompatibility antigen-specific naive and memory interleukin-2-secreting T cells within class I major histocompatibility complex (MHC)-restricted CD8+ and class II MHC-restricted CD4+ T-cell subsets

Recent studies have shown that host-reactive interleukin-2 (IL-2)-secreting donor T lymphocytes (TI) are critically involved in the development of acute graft-versus-host disease (GVHD) after allogeneic HLA-identical sibling bone marrow transplantation (BMT). To further characterize the responding TI, we determined the frequency of pretransplant IL-2-secreting TI-precursors (TI-p) between eight HLA-A, -B, -C, -DR, and -DQ-identical sibling donor-host pairs in both the graft-versus-host (GVH) and the host-versus-graft (HVG) direction. High frequencies of pretransplant host-reactive donor TI-p (1/18,000 to 1/49,000) were detectable in five patients with grade II acute GVHD. Donor-reactive host TI-p (1/3,700 to 1/31,000) were observed in previously in vivo primed (n = 5) and unprimed (n = 1) patients. In two pairs tested after previous in vivo priming, pretransplant donor-reactive host TI-p were highly enriched within the CD45RO+ memory T-cell subset. Previously unprimed host-reactive donor TI-p occurred in almost equal frequencies within CD45RO+ and CD45RO- T cells. Both CD4+ and CD8+ T-cell subsets contributed in comparable frequencies to host- and donor-reactive TI-p. Recognition of minor histocompatibility (mH) antigens by CD8+ TI-p appeared to be class I major histocompatibility complex (MHC)-restricted, whereas CD4+ TI-p operated in a class II (HLA-DR) MHC-restricted fashion. Even between oligonucleotide-defined HLA-DPB1-disparate sibling donor-host pairs (n = 3), either responding T-cell subset was found to recognize cellularly defined mH antigens. These data indicate that various T-cell subsets contribute to host- and donor-reactive IL-2-secreting TI in allogeneic sibling BMT.

Effect of heat shock on susceptibility of normal lymphoblasts and of a heat shock protein 70-defective tumour cell line to cytotoxic T lymphocytes in vitro

The effect of heat shock pretreatment of target cells on their lysability by cytotoxic T lymphocytes was analysed. Killing of Concanavalin A-stimulated normal lymphocytes by minor or major histocompatibility antigen-specific cytotoxic T lymphocytes is unchanged or even slightly enhanced after heat shock, whereas cells of the myeloma line Y3, which is derived from one of the lymphocyte donor strains, become nearly resistant to killing after the same pretreatment. Cold target inhibition experiments show that heat-shocked cells are recognized specifically and that untreated and heat-shocked target cells possess similar inhibitory potential. Y3 cells are unable to express the strongly heat-inducible heat shock protein of 70 kDa (hsp70) after heat shock; the acquired resistance is thus independent of hsp70 induction. Possible mechanisms of the different lysability seen in lymphoblasts and tumour cells after heat shock are discussed.

Effect of donor Langerhans cells on corneal graft rejection

Unlike other cutaneous surfaces, the central portion of the corneal epithelium is typically devoid of Langerhans cells. The absence of Ia+ Langerhans cells in the central cornea is of more than casual interest and may explain the immunologic privilege that is characteristic of corneal allografts. The present communication summarizes previous studies that examined the role of corneal Langerhans cells in eliciting alloimmune responses and corneal graft rejection in rodents. Under normal circumstances, corneal allografts are poorly immunogenic when residing in the avascular ocular graft bed even though the graft displays large quantities of alloantigens. The afferent blockade of the immune response can be circumvented by donor-derived Langerhans cells that serve as potent immunogens for all categories of corneal allografts except grafts involving allodisparity only at class I major histocompatibility complex loci. Thus, the presence of donor-derived Langerhans cells exerts profound effects on the fate of corneal allografts.

Effect of mismatches for major histocompatibility complex and minor antigens on corneal graft rejection

The importance of minor histocompatibility genes in corneal graft rejection was investigated using a model that simulates the major histocompatibility complex (MHC) and minor mismatches of the human allograft more accurately than previous animal models. DA(RT1a) x LEW(RT1(1]F1 hybrid rats were backcrossed to LEW, and the backcross generation were used as corneal graft recipients. Female DA(RT1a) strain animals were used as donors throughout. As in humans, the MHC disparity (a to 1) between each donor-recipient pair could be controlled; minor mismatches were variable and unknown. The MHC haplotype of each backcross individual (either homozygous l/l) or heterozygous a/l) was determined. Depending on this haplotype, the transplanted DA cornea was either matched or mismatched with the recipient for MHC antigens. The average proportion of minor disparate loci was 50%, although this was variable and unknown from recipient to recipient. Some animals of each MHC type were sensitized with three subcutaneous DA strain skin grafts at intervals of 2 weeks. Prior sensitization caused more rapid corneal graft rejection in both MHC mismatched (P less than 0.001) and matched (P less than 0.01) animals. All animals in the two MHC-mismatched groups (sensitized, 26; unsensitized, 17) and most in the MHC-matched groups (sensitized, 25 of 27; unsensitized, all 13) rejected their grafts. The MHC matching resulted in a greater range of survival times, although the difference in survival in unsensitized animals between matched and mismatched groups was not significant (unsensitized, P greater than 0.05; sensitized, P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory effect of herpes simplex virus infection to target cells on recognition of minor histocompatibility antigens by cytotoxic T lymphocytes

Target cell lysis by CTL specific for minor histocompatibility Ag (minor HA), which were generated in (C3H/He x BALB/c)F1 mice immunized with A/J mouse spleen cells, was dramatically reduced by infection of HSV to Neuro-2a (A/J mouse origin) cells as target. The reduction was apparent at 5 h after infection of HSV to target cells, when many viral proteins were produced in the cells. Conversely, MHC-restricted HSV-specific CTL-mediated cell lysis increased time dependently. Using an RNA virus, vesicular stomatitis virus, significant reduction of minor specific CTL-mediated target cell lysis was also found. During the time when this reduction of target cell lysis by HSV occurred, the surface expression of class I H-2Dd molecules was maintained, and anti-H-2a allo-MHC-specific CTL lysed HSV-infected Neuro-2a cells as strongly as uninfected Neuro-2a cells. When HSV-infected or uninfected Neuro-2a cells were treated with Brefeldin A that selectively blocks transportation of newly synthesized proteins out of endoplasmic reticulum, both HSV- and minor HA-specific CTL-mediated cell lyses were blocked. These observations demonstrated that minor HA are continuously synthesized and associated with class I molecules at pre-Golgi and transported via trans Golgi system with quick turnover, and that newly synthesized HSV Ag, which are also associated with class I molecules and transported via the same system, should take the place of intrinsic minor HA and be presented on the surface of the cells to be recognized by MHC-restricted CTL.