Restoration of H-2b expression and processing of endogenous antigens in the MHC class I pathway by fusion of a lymphoma mutant to L cells of the H-2k haplotype

Positive and negative regulation of Natural Killer cells: therapeutic implications

Natural Killer (NK) cells can mediate numerous anti-tumor and anti-viral effector functions as well as play important immunoregulatory roles in various disease states. Promoting the ability of NK cells to respond in an immunotherapeutic setting has often been sought by the addition of NK cell-stimulating factors. However, such therapies are often found to be insufficient, which may in part be due to the presence of inhibitory influences on the NK cell. NK cells can respond to a plethora of cytokines which are generated by numerous cell types and these interactions can markedly affect NK cell survival and activity. NK cells also possess multiple activating and inhibiting receptors which can alter their function. Whether the NK cell will become activated or not can depend on a complex balance of activating and inhibitory signals received by the cell and modulation of these signals may shift the balance on NK activation. This review discusses the various activating and inhibitory stimuli which can act on NK cells, and suggests that future NK cell-based therapies consider not only activating stimuli but also removal of possible inhibitory elements which could prevent optimal NK cell function and/or survival.

T cell receptor engagement by peptide-MHC ligands induces a conformational change in the CD3 complex of thymocytes

The T cell receptor (TCR) can recognize a variety of cognate peptide/major histocompatibility complex (pMHC) ligands and translate their affinity into distinct cellular responses. To achieve this, the nonsignaling alphabeta heterodimer communicates ligand recognition to the CD3 signaling subunits by an unknown mechanism. In thymocytes, we found that both positive- and negative-selecting pMHC ligands expose a cryptic epitope in the CD3 complex upon TCR engagement. This conformational change is induced in vivo and requires the expression of cognate MHC. We conclude that TCR engagement with a cognate pMHC ligand induces a conformational change in the CD3 complex of thymocytes and propose that this marks an initial event during thymic selection that signals the recognition of self-antigen.

Tumor-associated antigens identified by mRNA expression profiling as tumor rejection epitopes

Thirteen H-2b-binding peptides derived from six potentially overexpressed proteins in p53-/- thymoma (SM7) cells were studied for immunogenecity and vaccine-induced prevention of tumor growth in mice inoculated with SM7 tumor cells. Six of the peptides generated specific CTL responses after immunization, but only two of these peptides (RAD23-31 and RAD24-31) were capable of generating a weak vaccination-induced protection against adoptive tumor growth. SM7 inoculated mice treated with a blocking antibody against the inhibitory T cell signal transducing molecule CTLA4 appeared to delay tumor take, suggesting that SM7 thymoma cells are recognized by the adaptive immune system of the host. However, prophylactic vaccination with RAD23-31 and RAD24-31 peptides combined with anti-CTLA4 Ab treatment and did not improve tumor resistance. Our data would indicate that vaccination with immunogenic peptides derived from potentially overexpressed tumor proteins, as identified by mRNA expression profiling of p53-/- thymoma cells, at best results in a weak tumor protection thus questioning this way of detection of new tumor rejection epitopes.

The selective proteasome inhibitors lactacystin and epoxomicin can be used to either up- or down-regulate antigen presentation at nontoxic doses

The complete inhibition of proteasome activities interferes with the production of most MHC class I peptide ligands as well as with cellular proliferation and survival. In this study we have investigated how partial and selective inhibition of the chymotrypsin-like activity of the proteasome by the proteasome inhibitors lactacystin or epoxomicin would affect Ag presentation. At 0.5-1 microM lactacystin, the presentation of the lymphocytic choriomeningitis virus-derived epitopes NP118 and GP33 and the mouse CMV epitope pp89-168 were reduced and were further diminished in a dose-dependent manner with increasing concentrations. Presentation of the lymphocytic choriomeningitis virus-derived epitope GP276, in contrast, was markedly enhanced at low, but abrogated at higher, concentrations of either lactacystin or epoxomicin. The inhibitor-mediated effects were thus epitope specific and did not correlate with the degradation rates of the involved viral proteins. Although neither apoptosis induction nor interference with cellular proliferation was observed at 0.5-1 microM lactacystin in vivo, this concentration was sufficient to alter the fragmentation of polypeptides by the 20S proteasome in vitro. Our results indicate that partial and selective inhibition of proteasome activity in vivo is a valid approach to modulate Ag presentation, with potential applications for the treatment of autoimmune diseases and the prevention of transplant rejection.

Poor correspondence between predicted and experimental binding of peptides to class I MHC molecules

Naturally processed peptides presented by class I major histocompatibility complex (MHC) molecules display a characteristic allele specific motif of two or more essential amino acid side chains, the so-called peptide anchor residues, in the context of an 8-10 amino acid long peptide. Knowledge of the peptide binding motif of individual class I MHC molecules permits the selection of potential peptide antigens from proteins of infectious organisms that could induce protective T-cell-mediated immunity. Several methods have been developed for the prediction of potential class I MHC binding peptides. One is based on a simple scanning for the presence of primary peptide anchor residues in the sequence of interest. A more sophisticated technology is the utilization of predictive computer algorithms. Here, we have analyzed the experimental binding of 84 peptides selected on the basis of the presence of peptide binding motifs for individual class I MHC molecules. The actual binding was compared with the results obtained when analyzing the same peptides by two well-known, publicly available computer algorithms. We conclude that there is no strong correlation between actual and predicted binding when using predictive computer algorithms. Furthermore, we found a high number of false-negatives when using a predictive algorithm compared to simple scanning for the presence of primary anchor residues. We conclude that the peptide binding assay remains an important step in the identification of cytotoxic T lymphocyte (CTL) epitopes which can not be substituted by predictive algorithms.

Kupffer cell staining by an HFE-specific monoclonal antibody: implications for hereditary haemochromatosis

Hereditary haemochromatosis is an inherited disorder of iron absorption that leads to excessive iron storage in the liver and other organs. A candidate disease gene HFE has been identified that encodes a novel MHC class I like protein. We report the development of a monoclonal antibody (HFE-JB1) specific for recombinant refolded HFE protein. The antibody immunoprecipitates a 49 kD protein from the cell line U937, a histiocytic lymphoma. It binds HFE but does not recognize other recombinant non-classic MHC class I proteins (HLA-E, F and G), nor does it react with a variety of recombinant classic class I MHC molecules. COS cells transfected with HFE in culture are stained specifically. The immunohistochemical staining pattern in human tissues is unique and can be defined as a subset of the transferrin receptor positive cells. In the liver HFE protein was shown to be present on Kupffer cells and endothelium (sinusoidal lining cells), but absent from the parenchyma. Kupffer cells from an untreated C282Y HH patient failed to stain with the antibody. In the normal gut scattered cells in the crypts are stained. HFE was also present on capillary endothelium in the brain (a site of high levels of transferrin receptor) and on scattered cells in the cerebellum and cortex. These results raise interesting questions concerning the function of HFE in the control of body iron content and distribution.

Eliciting T Cell Immunity Against Poorly Immunogenic Tumors by Immunization with Dendritic Cell-Tumor Fusion Vaccines

Dendritic cells (DCs) are the most effective APCs and are being studied as natural adjuvants or Ag delivery vehicles to elicit T cell-mediated antitumor immunity. This study examined whether inoculation of DCs fused with poorly immunogenic tumor cells elicited tumor-reactive T cells for adoptive immunotherapy. DCs derived from bone marrow of C57BL/6 (B6) mice were fused with syngeneic B16 melanoma or RMA-S lymphoma cells by polyethylene glycol. The B16/DC and RMA-S/DC fusion hybrids expressed MHC class I, class II Ags, costimulatory molecules, as well as DC-specific and tumor-derived surface markers. The tumor/DC hybrids were capable of processing and presenting tumor-derived Ags, and immunization of B6 mice with irradiated B16/DC or RMA-S/DC vaccine elicited tumor-specific CTL activities. Vaccination of B6 mice with irradiated B16/DC fusion preparations induced partial host protective immunity against B16 tumor challenge. Reduced tumor incidence and prolonged survival time were observed. Adoptive transfer of T cells derived from B16/DC vaccine-primed lymph nodes into B16 tumor-bearing mice greatly reduced the number of established pulmonary metastases with or without in vivo administration of IL-2. Moreover, adoptive transfer of RMA-S/DC vaccine-primed, cultured lymph node T cells eradicated disseminated FBL-3 tumor. The results demonstrate that tumor/DC fusion products are effective cellular vaccines for eliciting T cell-mediated antitumor immunity.

A protective cytotoxic T cell response to a subdominant epitope is influenced by the stability of the MHC class I/peptide complex and the overall spectrum of viral peptides generated within infected cells

This study identifies instability of MHC class I/peptide complexes and intermolecular competition for MHC class I presentation as factors responsible for the subdominance of cytotoxic T lymphocyte (CTL) epitopes. This evidence is based on the characterization of a new CTL epitope derived from the glycoprotein (GP) of lymphocytic choriomeningitis virus (LCMV). This epitope, peptide GP117-125 (GP117) is presented to T cells by the mouse MHC class I molecule, H-2Db. In short-term experiments induction of GP117-specific CTL by vaccination rendered C57BL/6 mice only partially resistant to infection with wild-type LCMV (LCMV-WE) but completely resistant to challenge with a previously described LCMV variant. The variant virus, LCMV-8.7B23, bears point mutations within both known LCMV-GP, H-2 Db-restricted epitopes GP33-41 (GP33) and GP276-286 (GP276) resulting in a valine to leucine change at position 35 in peptide GP33 (V35L) and an asparagine to serine change at position 280 in peptide GP276 (N280S). Although variant peptide GP33/V35L stimulates a weak CTL response, GP276/N280S does not. Elution of peptide GP117 from both LCMV-WE- and LCMV-8.7B23-infected cells revealed that the difference in the capacity of GP117-specific CTL to protect against LCMV-WE and the virus variant LCMV-8.7B23 was due to differences in the level of GP117 presentation on the surface of both types of cells. Thus, it appears that the protective capacity of CTL specific for the subdominant epitope GP117 is influenced by the extent of presentation of other immunodominant peptide epitopes present within infected cells.

Protective immunity does not correlate with the hierarchy of virus-specific cytotoxic T cell responses to naturally processed peptides

Infection of C57BL/6 mice with lymphocytic choriomeningitis virus (LCMV) stimulates major histocompatibility complex class I-restricted cytotoxic T cells (CTLs), which normally resolve the infection. Three peptide epitopes derived from LCMV have been shown to bind the mouse class I molecule H-2 Db and to stimulate CTL responses in LCMV-infected mice. This report describes the identity and abundance of each CTL epitope after their elution from LCMV-infected cells. Based on this information, peptide abundance was found to correlate with the magnitude of each CTL response generated after infection with LCMV. Subsequent experiments, performed to determine the antiviral capacity of each CTL specificity, indicate that the quantitative hierarchy of CTL activity does not correlate with the ability to protect against LCMV infection. This report, therefore, indicates that immunodominant epitopes should be defined, not only by the strength of the CTL response that they stimulate, but also by the ability of the CTLs to protect against infection.

Protective Immunity Does Not Correlate with the Hierarchy of Virus-specific Cytotoxic T Cell Responses to Naturally Processed Peptides

Infection of C57BL/6 mice with lymphocytic choriomeningitis virus (LCMV) stimulates major histocompatibility complex class I–restricted cytotoxic T cells (CTLs), which normally resolve the infection. Three peptide epitopes derived from LCMV have been shown to bind the mouse class I molecule H-2 Db and to stimulate CTL responses in LCMV-infected mice. This report describes the identity and abundance of each CTL epitope after their elution from LCMV-infected cells. Based on this information, peptide abundance was found to correlate with the magnitude of each CTL response generated after infection with LCMV. Subsequent experiments, performed to determine the antiviral capacity of each CTL specificity, indicate that the quantitative hierarchy of CTL activity does not correlate with the ability to protect against LCMV infection. This report, therefore, indicates that immunodominant epitopes should be defined, not only by the strength of the CTL response that they stimulate, but also by the ability of the CTLs to protect against infection.

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.

Recognition of carbohydrate by major histocompatibility complex class I-restricted, glycopeptide-specific cytotoxic T lymphocytes

Cytotoxic T cells (CTL) recognize short peptide epitopes presented by class I glycoproteins encoded by the major histocompatibility complex (MHC). It is not yet known whether peptides containing posttranslationally modified amino acids can also be recognized by CTL. To address this issue, we have studied the immunogenicity and recognition of a glycopeptide carrying an O-linked N-acetylglucosamine (GlcNAc) monosaccharide-substituted serine residue. This posttranslational modification is catalyzed by a recently described cytosolic glycosyltransferase. We show that glycosylation does not affect peptide binding to MHC class I and that glycopeptides can elicit a strong CTL response that is glycopeptide specific. Furthermore, glycopeptide recognition by cytotoxic T cells is dependent on the chemical structure of the glycan as well as its position within the peptide.

Peptide transporter-independent, stress protein-mediated endosomal processing of endogenous protein antigens for major histocompatibility complex class I presentation

The peptide transporter-defective cell line RMA-S expressing the wild-type simian virus 40 large T antigen (wtT-Ag) from a transfected gene did not present two well-defined, H-2 class I (Db)-restricted epitopes of T-Ag to cytotoxic T lymphocytes (CTL). Hence, "endogenous" processing and presentation of the wtT-Ag depended on a functional peptide transporter heterodimer. In contrast, both T-Ag epitopes were efficiently presented to CTL by transfected RMA-S cells expressing a truncated, cytoplasmic T-Ag variant (cT-Ag) or a karyophilic, amino-terminal 272-amino acid T-Ag fragment. Transporter-independent "endogenous" processing of mutant T-Ag molecules correlated with their association with the constitutively expressed heat shock protein 73 (hsp73). Class I-restricted presentation of both epitopes processed from these hsp73-associated protein antigens was sensitive to NH4Cl and chloroquine. These data indicate that selected intracellular proteins access an alternative, hsp73-mediated pathway for class I-restricted presentation that operates independent of peptide transporters in an endosomal compartment.

The CD8+ T cell repertoire in beta 2-microglobulin-deficient mice is biased towards reactivity against self-major histocompatibility class I

Beta 2-Microglobulin-deficient (beta 2m -/-) mice are reported to lack cell surface expression of major histocompatibility complex (MHC) class I molecules, CD8+ T cells, and the ability to mount MHC class I-specific T cell responses. We have observed that beta 2m -/- mice possess CD8+ T cells that can be induced to perform strong allospecific cytotoxic responses against nonself-MHC class I by in vivo priming. We report that these beta 2m -/- cytotoxic T lymphocyte (CTL) differ from those induced in beta 2m-positive littermates in that they cross-react and kill cells expressing self-MHC class I at normal ligand density with beta 2m. beta 2m -/- CTL could even be induced in primary mixed lymphocyte culture by self-MHC class I expressing stimulator cells, whereas allogeneic stimulator cells failed to elicit a response under similar conditions. Cells with a reduced cell surface MHC class I expression were less sensitive, while syngeneic beta 2m -/- cells were resistant to the beta 2m -/- CTL. This antiself-MHC reactivity could not be induced when beta 2m -/- T cells matured in an environment with normal MHC class I expression in bone marrow chimeric mice. Antiself-MHC reactivity was also observed against human peptide loading-deficient cells expressing the appropriate murine class I molecules, suggesting that affinity to self-MHC class I may occur irrespective of peptide content. The results fit with a model where positive and negative selection of CD8+ T cells in beta 2m -/- mice is mediated by low levels of MHC class I free heavy chains. In this model, low ligand density on selecting cells leads to positive selection of rare T cells that bind to low levels of MHC class I free heavy chains, resulting in a very small peripheral CD8+ compartment. Due to low density of the selecting ligand, negative selection does not remove T cells recognizing beta 2m-positive cells expressing self-MHC class I at normal ligand density, which generates a T cell repertoire that would be autoreactive in a beta 2m-positive littermate. The first "MHC deficient" animals thus paradoxically provide a tool for direct demonstration and analysis of self MHC bias in the T cell repertoire.

Recognition of vaccinia virus-encoded major histocompatibility complex class I antigens by virus immune cytotoxic T cells is independent of the polymorphism of the peptide transporters

In the cytotoxic T-cell response to viruses, peptide antigens of cytoplasmic origin are presented at the cell surface by the highly polymorphic major histocompatibility complex (MHC) class I molecules to CD8+ T-lymphocyte receptors. Peptide transporter molecules and other MHC-linked gene products have been implicated in the generation and import of antigenic peptides into the lumen of the endoplasmic reticulum for assembly with MHC class I glycoproteins. These accessory molecules in the antigen-presentation pathway map to a polymorphic region in the class II MHC, and the possibility of their allele-specific selectivity in antigen presentation has been raised. Here we show that additional, functionally polymorphic components are not apparent in an in vitro mouse MHC class I-restricted cytotoxic T-cell response to vaccinia and influenza viruses. When the mouse H-2Kd molecule was expressed via a recombinant vaccinia virus in target cells of different mouse MHC haplotypes or cells of rat, Syrian hamster, monkey, and human origin, efficient Kd-restricted and vaccinia virus-specific lysis was observed as measured with bulk effectors and at the clonal level. In addition, human transporters efficiently processed peptides originating from influenza virus nucleoprotein and hemagglutinin antigens as recognized by mouse influenza immune cytotoxic T cells.

Peptide-induced stabilization and intracellular localization of empty HLA class I complexes

The human cell line T2 has been reported to be class I assembly deficient, and accordingly expresses reduced amounts of HLA-A2 and no HLA-B5 at the cell surface. By immunoblotting we observe the steady-state class I heavy chain levels of T2 to be near normal when compared with the identical class I alleles of the wild-type cell line T1. In pulse chase experiments, formation of heavy chain beta 2-microglobulin complexes is observed for both HLA-A2 and HLA-B5. Culture at reduced temperatures (26 or 20 degrees C) does not increase the amount of class I molecules transported, unlike what has been reported for the class I assembly-deficient mouse mutant cell line RMA-S. The HLA-B5 and the HLA-A2 complexes formed by T2 are thermolabile in cell lysates, albeit to different degrees. The thermolability of HLA-B5 can be overcome by addition of HLA-B5-presentable peptides, obtained by trifluoroacetic acid extraction from an HLA-B5-positive cell line, underlining the necessity of peptide for class I stability and indicating that T2-derived class I complexes are devoid of peptide. Cytoplast fusion of T2 cells with RMA-S cells shows the defect in class I assembly of RMA-S to be similar to that of T2. Localization of class I molecules observed by immuno-electron microscopy reveals the accumulation in the T2 cell line of both HLA-B5 and HLA-A2 in the endoplasmic reticulum (ER). Class I molecules are present in all the cisternae of the Golgi complex of T2, but the ratio of HLA-A and -B locus products in the Golgi area differs significantly from that at the cell surface. We conclude that the requirement for peptide in transport of class I molecules manifests itself at a stage beyond the ER, most likely the Golgi area.

An endogenous antigenic peptide bypasses the class I antigen presentation defect in RMA-S

The RMA-S cell line was derived from the Raucher virus-induced murine cell line RBL-5 by ethylmethane sulfonate mutagenesis and anti-H-2 antibody plus complement selection (Ljunggren, H.-G., and K. Karre. 1985. J. Exp. Med. 162:1745). RMA-S is defective in the ability to present endogenously synthesized antigens to class I major histocompatibility complex (MHC)-restricted cytotoxic T lymphocytes (CTL) (Townsend, A., C. Ohlen, J. Bastin, H.-G. Ljunggren, L. Foster, and K. Karre. 1989. Nature [Lond.]. 340:443; Ohlen, C., J. Bastin, H.-G. Ljunggren, L. Foster, E. Wolpert, G. Klein, A. R. M. Townsend, and K. Karre. 1990. J. Immunol. 145:52). This defect has been attributed to the inability of RMA-S to deliver antigenic peptides derived from antigens in the cytosol into the endoplasmic reticulum (ER), where they can associate with class I MHC molecules (Townsend, A., C. Ohlen, J. Bastin, H.-G. Ljunggren, L. Foster, and K. Karre. 1989. Nature [Lond.]. 340:443). We show that RMA-S can present at least one endogenous antigen, vesicular stomatitis virus nucleoprotein (VSV-N), to class I MHC-restricted CTL. RMA-S presents VSV-N to CTL both when infected with VSV or transfected with the VSV nucleoprotein gene. The natural antigenic VSV nucleoprotein peptides purified from either RMA or RMA-S are indistinguishable when analyzed by high performance liquid chromatography. We also show that the genetic defect responsible for the RMA-S phenotype maps to the murine chromosome 17. This chromosome encodes the murine class I MHC genes as well as two genes, HAM-1 and -2, with homology to the adenosine triphosphate-dependent transporter superfamily (Monaco, J. J., S. Cho, and M. Attaya. 1990. Science [Wash. DC]. 250:1723). These results suggest that the system that delivers antigenic peptides from the cytosol to the ER in RMA-S may still be present and retain partial function.

RMA/S cells present endogenously synthesized cytosolic proteins to class I-restricted cytotoxic T lymphocytes

RMA/S is a mutant cell line with decreased cell surface expression of major histocompatibility complex class I molecules that has been reported to be deficient in presenting endogenously synthesized influenza virus nucleoprotein (NP) to cytotoxic T lymphocytes (CTL). In the present study we show that RMA/S cells can present vesicular stomatitis virus nucleocapsid protein, and, under some conditions, NP, to Kb-and Db-restricted CTL, respectively. Antigen presentation results from processing of cytosolic pools of endogenously synthesized proteins, and not the binding to cell surface class I molecules of antigenic peptides present in the virus inoculum or released from infected cells. Antigen processing of RMA/S differs, however, from processing by wild-type cells in requiring greater amounts of antigen, longer times to assemble or transport class I-peptide complexes, and in being more sensitive to blocking by anti-CD8 antibody. Thus, the antigen processing deficit in RMA/S cells is of a partial rather than absolute nature.

The RMA-S lymphoma mutant; consequences of a peptide loading defect on immunological recognition and graft rejection

Experiments with mutant cell lines have underscored the role for peptide in maintenance of the structure of major histocompatibility complex (MHC) class-I molecules. The class-I molecules act as receptors for antigenic and "self" peptides derived from degraded intracellular synthesized proteins. The class-I/peptide trimeric complex is transported to the cell surface where it is scrutinized by cytotoxic T lymphocytes (CTL). The murine RMA-S mutant cell lines have a defect in class-I assembly and express markedly reduced levels of class-I molecules at the cell surface. The mutation is consistent with a defect in peptide transport from the cytosol to the place of assembly with class-I molecules. Addition of synthetic peptides to RMA-S cells and RMA-S cell lysates stimulates assembly of the class-I molecules and indicates that peptide plays a crucial role in attaining the class-I structure. Recent findings have demonstrated that class-I heavy clains (HCs) and beta 2 microglobulin (beta 2m) can assemble in absence of synthetic peptides, forming presumably "empty" (non-peptide-containing) class-I dimeric complexes, in RMA-S cells cultured at reduced temperature. The few class-I molecules present on RMA-S cultured at physiological temperature share the phenotype of "empty" class-I molecules induced at reduced temperature. This finding has allowed the re-interpretation of earlier studies and opened new ways to analyze the interaction between MHC-class-I molecules and different effector cells such as allo-specific CTLs, class-I-restricted CTLs and natural killer (NK) cells. In addition, recent data also suggest that RMA-S represents an attractive model for examining direct class-I-peptide interactions on intact cells or in cell lysates.

High-resolution one-dimensional isoelectric focusing of mouse MHC class I antigens. Identification of natural and experimentally induced class I antigens

A method is described for a biochemical comparison of mouse class I antigens utilizing antisera with a monomorphic pattern of reaction and high-resolution one-dimensional isoelectric focusing (1D-IEF). The most commonly occurring and studied H-2K and D alleles were identified in a comparison of over 40 mouse strains. By comparing H-2 mutant mouse strains, cell lines transfected with defined class I genes, or mice transgenic for a mouse class I gene and H-2 recombinant mouse strains, unambiguous identification of class I alleles was possible. The complex pattern presented by H-2-heterozygous mice was readily resolved into the contribution by the individual parental alleles. The H-2b bm series of mutants was analyzed, and for those mutants where a charge difference was predicted based on their known sequence, a change in isoelectric point (IEP) was indeed observed. Based on analysis by IEF, the bm8 mutant may contain (an) amino acid substitution(s) in addition to those reported. The present method further appears useful in elucidating defects in class I antigen synthesis and post-translational modifications, as these cannot be easily characterized when using surface staining with monoclonal antibodies (mAbs).