Role of glycosylation in the H-2-restricted cytolysis of virus-infected cells

Cell type and maturation stage-dependent polymorphism of N-linked oligosaccharides on murine lymphocytes and lymphoma cells

We analyzed the overall structures of N-linked oligosaccharides on glycoproteins of various murine lymphocytic and lymphoma cells employing a newly developed method which was performed on high-performance liquid chromatography after derivatization of oligosaccharides with 2-aminopyridine. A total of 15 types of bi, tri- and tetra-antennary N-acetyllactosamine-type oligosaccharides with or without fucose and oligomannose-type oligosaccharides were identified on these cells in variable amounts depending on the type and maturation stage of the cells. It was found that all murine lymphocytic cells carry N-acetyllactosamine-type oligosaccharides with the additional alpha-linked galactose residue on the non-reducing ends. Thymocytes had exceptionally large amounts of oligosaccharides with one or even two alpha-galactose residues per molecule. In contrast, peripheral resting T cells possessed those oligosaccharides only in a small amount, although the cells produced more the oligosaccharides after stimulation with Con A. Two thymoma lines such as BW 5147 and EL-4 and one B cell lymphoma line WEHI231 contained relatively large amount of oligosaccharides with alpha-galactose residues. Significant change of the molar ratio of component carbohydrates by cell activation was observed also in oligommanose-type oligosaccharides which were few in resting T cells but were markedly increased in Con A activated cells. Molar ratio of triantennary oligosaccharides in total N-acetyllactosamine type oligosaccharides was high in thymocytes and low in resting T cells, but was increased in T cells after Con A activation. It was also very high in WEHI 231 B cell lymphoma. Although BW 5147 and EL-4 thymoma did not contain tri-antennary oligosaccharides in high proportion, they carried larger tetra-antennary oligosaccharides with an N-acetyllactosamine repeating unit in definitive amounts. It is suggested from these results that overall structures of oligosaccharides on cell surface proteins of lymphocytes are finely controlled with link to cell differentiation, activation and transformation.

Modulation of the secondary antibody response of murine lymphocytes to sheep red blood cells in vitro by neuraminidase and exoglycosidases

The effect of digestion of lymphocytes with neuraminidase and exoglycosidases on the secondary antibody response in vitro to sheep red blood cell (SRBC) antigen was tested. Treatment of spleen cells from SRBC-primed mice with 3 micrograms/ml of neuraminidase slightly but significantly augmented their plaque-forming cell response to SRBC, whereas treatment with 100 micrograms/ml of a mixture of exoglycosidases did not. Rather unexpectedly, however, treatment of the spleen cells with the mixture of both neuraminidase and exoglycosidases greatly augmented the response. This enzyme action was substrate specific inasmuch it was ablated by addition of mucin as a neuraminidase inhibitor to the enzyme mixture. The target of the enzyme activity was not glass-adherent macrophages, but was glass-non-adherent suppressor cells in the antigen-primed cell population. Evidence was provided that the phenotype of suppressor cells whose activity was ablated by the enzyme treatment was Thy-1+. It is suggested from these results that sialylated complex type oligosaccharides on antigen-primed T cells play a critical role in their suppressor activity.

A trans-acting major histocompatibility complex-linked gene whose alleles determine gain and loss changes in the antigenic structure of a classical class I molecule

The RT1.A locus of the rat MHC encodes the H chain of the single classical class I molecule of this species. One of the alleles of this polymorphic locus, RT1.Aa, is present in several laboratory inbred, congenic, and MHC recombinant rat strains. Studies of the RT1.Aa class I molecule from a number of these strains as a target for CTL show that its antigenicity, both as an alloantigen and a restricting element, is subject to gain and loss alterations by the action of a gene mapping in the MHC to the right of RT1.A. This locus is apparently present in two allelic forms (one possibly a null allele) corresponding to the presence or absence of a dominant transacting modifier, and has been named class I modification, or cim. The antigenic change brought about by cim is scarcely detectable serologically but highly immunogenic for CTL. Biochemical investigations show that cim affects the post-translational modification of RT1.Aa.

Differential expression of MHC class I antigens on the placenta of the rat. A mechanism for the survival of the fetal allograft

In some mating combinations in rats, there is a maternal antibody response to the maternal antigenic components of the placenta without any previous immunization of the mother. The highest response occurs in the WF (u) female mated to the DA (a) male, and it is against a unique MHC-encoded class I antigen, the Pa antigen, and not against the major allele-specific transplantation antigen of the DA strain, RT1.Aa. The development of mAbs to the Pa and Aa antigens allowed us to localize these antigens on the placenta and to explore the reason for the differential antibody response to them using immunohistochemical and biochemical techniques. Both antibodies reacted with the WF X DA placenta and stained the endovascular and interstitial trophoblast of the decidua, the basal trophoblast, Reichert's membrane, and the yolk sac epithelium, but they did not stain the labyrinthine trophoblast. Blocking studies showed that each antibody reacted with a separate molecule in the placenta. Anti-class II mAbs reactive with the a or u haplotype did not stain the WF X DA, DA X DA, or WF X WF placenta; hence, there are no class II antigens in the placenta. Electron microscopic studies of the semiallogeneic WF X DA placenta using the immunogold technique with both single- and double-labeling showed that only the Pa antigen was expressed on the surface of the basal trophoblast, but that both the Pa and Aa antigens were in the cytoplasm of these cells; neither antigen was found in the labyrinthine trophoblast. By contrast, the placenta from the syngeneic DA X DA mating expressed both the Pa and Aa antigens on the surface of the basal trophoblast as well as in the cytoplasm; neither antigen was found in the labyrinthine trophoblast. These observations were quantified morphometrically using electron photomicrographs of single-labeled tissues. Both the Pa and Aa antigens isolated from the plasma membrane of lymphocytes have heavy chains of 46 kD, but those antigens isolated from the plasma membrane of basal trophoblast cells have heavy chains of 43 kD. Based on densitometric measurements of autoradiographs, the Pa/Aa ratio in the basal trophoblast membrane is 23.5, whereas it is 0.46 in lymphocyte membranes. These studies show that there is differential regulation of the expression of class I antigens on basal trophoblast cells in semiallogeneic pregnancies, but not in syngeneic pregnancies, such that the major allele-specific transplantation antigen is scarcely expressed on the surface of the basal trophoblast.(ABSTRACT TRUNCATED AT 400 WORDS)

Site-directed mutagenesis of class I HLA genes. Role of glycosylation in surface expression and functional recognition

We have investigated the role of the carbohydrate moiety on the HLA-B7 molecule in mAb and CTL recognition using oligonucleotide-directed mutagenesis and gene transfer techniques. A conservative substitution of asparagine to glutamine at amino acid 86 in HLA-B7 was created to abolish the unique glycosylation site present on all HLA molecules. A second mutant B7 molecule was made by substituting asparagine-aspartic acid-threonine for the resident lysine-aspartic acid/lysine tripeptide at amino acids 176-178, thus creating an N-linked glycan at amino acid 176, which is additionally present on all known murine H-2 class I antigens. Upon gene transfer into mouse and human cell recipients, the HLA-B7M176+ mutant and normal HLA-B7 expressed identical levels of surface protein. However, the binding of two mAbs (MB40.2 and MB40.3) thought to recognize different epitopes of the HLA-B7 molecule was completely eliminated. In contrast, the HLA-B7M86- mutant displayed no surface expression (mouse L cells) or minimal surface expression (human RD cells or mouse L cells coexpressing human beta 2 microglobulin [beta 2m]) after indirect immunofluorescence (IIF) and flow cytometric analysis with a panel of 12 HLA-B7 mAb reactive with monomorphic and polymorphic determinants. Immunoprecipitation analysis demonstrated that intracellular denatured mutant protein was present. Tunicamycin treatment did not rescue the expression of HLA-B7M86- antigens to the cell surface; while interferon did induce higher levels of surface expression. Tunicamycin treatment also did not allow binding of the mAbs MB40.2 or MB40.3 to HLA-B7M176+ mutant antigens, suggesting that the carbohydrate moiety itself was not directly involved in the recognition or conformation of these mAb epitopes. Further mutation of the B7M86- molecule to create a glycan moiety at amino acid position 176 (B7M86-/176+) did not rescue normal levels of surface expression. Finally, neither mutation was seen to affect recognition by a panel of 12 allospecific CTL clones. The low expression of HLA-B7M86- on the surface of human cell transfectants was sufficient to achieve lysis, albeit at a reduced efficiency, and lysis could be increased by interferon induction of higher levels of expression. Thus, the carbohydrate moiety on HLA antigens plays a minimal or nonexistent role in recognition by available mAb and allospecific CTL clones.

Inhibitory effects of tunicamycin on the mixed lymphocyte reaction and mitogen-induced lymphocyte blastogenesis

The role of asparagine(Asn)-linked saccharides on the surface of lymphocytes in cellular interactions was examined by performing studies on the effects of tunicamycin (TM), which inhibits the glycosylation of proteins N-glycosylated at asparagine residues, on the mixed lymphocyte reaction (MLR) and mitogen-induced lymphocyte blastogenesis of human lymphocytes by measuring 3H-thymidine (TdR) incorporation. Responses were expressed as percentages of that of the control (MLR without TM). The lymphocyte blastogenesis in the one- and two-way MLR were, respectively, 43.1% and 48.0% of the control at 0.1 microgram/ml of TM, and 5.5% and 7.2% at 1 microgram/ml of TM. The inhibitory effect of TM on the one-way MLR was shown using TM-pretreated stimulator cells, TM-pretreated responder cells or both. TM blocked lymphocyte blastogenesis in the secondary as well as in the primary MLR. The inhibitory effect of TM on the two-way MLR was observed when TM was added on day 0 to day 2, but not on day 4 of incubation. TM blocked mitogen-induced lymphocyte blastogenesis by phytohemagglutinin, concanavalin A or by pokeweed mitogen. As TM had no cytotoxic effect on cultured cells, these inhibitory effects of TM were thought to be due to the loss of Asn-linked saccharides from glycoprotein of the surface of lymphocytes. These findings indicated that Asn-linked saccharides of glycoprotein on the surface of lymphocytes were important in cellular interactions that are necessary for the cellular immune response.

Cell-surface expression of H-2Db requires N-linked glycans

The question of whether beta-2 microglobulin (B2m)-independent expression of the mouse major histocompatibility complex (MHC) antigen H-2Db results from the atypical glycosylation pattern associated with this MHC antigen (i.e., three glycans instead of two) has been addressed. Cell-surface expression of transfected H-2Db in the B2m deficient cell line R1E was completely abolished by the drug tunicamycin (Tm). Introduction of a functional B2m gene by transfection did not re-establish cell-surface expression of Db in the presence of Tm. Tm had no effect, however, on the expression of a truncated Db molecule lacking the alpha 1 and alpha 2 domains which is glycosylated at amino acid position 256, suggesting that the Db molecule, unlike other class I antigens, possesses an unstable conformation in the alpha 1 and/or alpha 2 domains which requires the attachment of glycans before it is transported to the cell surface. Once attached, however, glycans may confer a stable alpha 1/alpha 2 conformation apparently peculiar to Db which allows cell-surface expression in the absence of B2m.

A structural analysis of the carbohydrate side chains on class I and class II histocompatibility antigens of the swine facilitated by heteroantisera specific for the denatured polypeptides

Rabbit heteroantisera specific for the denatured glycoprotein subunits of swine class I and class II major histocompatibility complex (MHC) antigens have been prepared and utilized to monitor changes in the mobilities of these polypeptides on SDS-polyacrylamide gel electrophoresis subsequent to various deglycosylation procedures. This information, in combination with lectin reactivity patterns for the glycoproteins bound to nitrocellulose, has made it possible to define specific structural features of the MHC antigen-associated carbohydrate side chains. Both the class I heavy (alpha) chain and the class II light (beta) chain bear a single, N-linked, complex-type oligosaccharide which reacts with lentil lectin (LcH), but not concanavalin A (Con A); a reactivity pattern suggesting the possibility of a special triantennary structure. In contrast, the class II heavy (alpha) chains appear to possess two carbohydrate units, one an N-linked, LcH-reactive, complex-type side chain, and the other, an N-linked, Con A-reactive, high-mannose-type of oligosaccharide. The data suggest considerable homology between the swine and human MHC antigens with respect to the structure of their carbohydrate side chains. The analysis also serves to illustrate how antibodies specific for the denatured polypeptide backbone of individual glycoproteins, along with lectin reactivity patterns, can be used to extract structural information about the attached carbohydrate moieties using minimal amounts of partially purified glycoproteins.

N-Linked oligosaccharides of the H-2Dk histocompatibility protein heavy chain influence its transport and cellular distribution

The H-2K and H-2D proteins encoded by the K and D region of the major histocompatibility complex of the mouse were isolated by immunoprecipitation with specific antisera and resolved by two-dimensional gel electrophoresis. Of these two polypeptides, the H-2Dk glycoproteins isolated from macrophages of C3H/HeHa mice exhibit distinct cell surface and cytoplasmic forms although they share a strong degree of homology in the polypeptide backbone. Structurally they differ in their oligosaccharide structures. The structure of the oligosaccharides on the intracellular forms is of the high mannose type while the same structures on the cell surface forms are of the complex type. In the absence of all three oligosaccharide side chains, the unglycosylated polypeptides are expressed on the cell surface. In contrast, polypeptides containing one, two, or all three oligosaccharide side chains of the high mannose type are not transported to the cell surface. Cell surface expression of these glycoproteins requires processing of the oligosaccharide side chains from the high mannose form to the complex type. However, not all oligosaccharide antennae have to be terminally modified since H-2Dk glycoproteins synthesized in the presence of oligosaccharide-processing enzyme inhibitors such as swainsonine or monensin are also transported to the cell surface. H-2Dk glycoproteins containing oligosaccharide structures of the complex type but lacking terminal sialic acids are found on the cell surface, suggesting that sialylation is not required for transport. These results indicate that the oligosaccharide structures of the H-2Dk glycoproteins act to influence their cellular distribution.

Carbohydrate moieties of major histocompatibility complex class I alloantigens are not required for their recognition by T lymphocytes

The ability to generate specific cytotoxic responses using purified major histocompatibility complex (MHC) antigen in liposomes has made it possible to directly assess the importance of class I carbohydrate moieties in T cell recognition of alloantigen. Deglycosylation of affinity-purified H-2Kk to yield a single glycan-free product did not alter the specificity, the magnitude, nor the dose range of the cytotoxic T lymphocyte (CTL) response to the class I antigen. It can be concluded that carbohydrate moieties are not required to maintain the necessary conformation of the MHC protein, nor to interact with either the antigen-specific receptor or accessory proteins on precursor CTL.

Modification of blood-borne arrest properties of lymphoma cells by inhibitors of protein glycosylation suggests the existence of endogenous lectins

The requirement for intact carbohydrates of glycoproteins at the cell surface was investigated after treatment of lymphoma cells with compounds which interfere at different steps in N-linked glycosylation: swainsonine and 1-deoxynojirimycin act at different levels during the processing, so that complex oligosaccharides cannot be formed; 2-deoxyglucose, beta-hydroxynorvaline, and tunicamycin completely prevent the formation of N-linked (high-mannose as well as complex) oligosaccharides. The role of sialic acid was investigated by treating the cells with neuraminidase. These treatments resulted in altered patterns of surface-labelled glycoproteins after SDS-polyacrylamide gel electrophoresis. Blood-borne arrest of lymphoma cells in the spleen was sensitive to neuraminidase and to treatments interfering with the processing of complex N-linked oligosaccharides. It is suggested that carbohydrates are signals for cellular interactions involved in the recirculation and homing behaviour of lymphoid cells and probably interact with endogenous lectins at their site of homing.

Selective binding of concanavalin A to target cell major histocompatibility antigens is required to induce nonspecific conjugation and lysis by cytolytic T lymphocytes in lectin-dependent cytotoxicity

The exquisite immunological specificity of cytotoxic T lymphocytes-target cell (CTL-TC) conjugation and lysis is overridden in the presence of certain plant lectins. The role of concanavalin A (Con A) in lectin-dependent, CTL-mediated cytolysis (LDCC) has been investigated. Papain-treated TC are refractory to LDCC, but regain susceptibility following a 3-hr incubation without the enzyme. Papain-treated TC allowed to recover in the presence of tunicamycin (TM; an inhibitor of N-linked glycosylation), are totally refractory to LDCC. Refractoriness of TM-treated TC to LDCC is not due to an overall resistance to lysis or to lack of Con A binding, as these cells can be lysed by specifically sensitized CTL or by H-2 antibody and complement and display a sufficiently high Con A-binding capacity, indistinguishable from intact TC, probably through O-linked, cell-surface glycosyl residues. The finding that TC (TM-treated) capable of binding normal Con A quantities cannot, however, engage in lectin-dependent CTL-TC conjugation and lysis indicates that Con A must react selectively with a specific TC-surface component(s), thereby rendering the TC recognizable by effector CTL, rather than by simply bridging ("glueing") CTL and TC. Affinity absorption and elution from Sepharose-Con A beads as well as specific immunoprecipitations by antibodies against cell surface determinants, have shown effective Con A binding to TC surface components of molecular weights corresponding to 45-kDa product of the H-2K and D MHC genes and, possibly, to a 30-kDa component. Antibodies against MHC proteins but not against non-MHC surface proteins of the TC have produced effective inhibition of LDCC. This and previous investigations show that in nonspecific LDCC as in specific CTL-mediated lysis, TC-MHC determinants are involved in signaling TC recognition and lysis.

Hypothesis: the MHC-restricted T-cell receptor as a structure with two multistate allosteric combining sites

This paper presents a dual-recognition model of the T-cell receptor that has been constructed to account for the phenomenon of MHC restriction as well as the paradoxical ability of T-cells to be both multispecific and precisely specific at the same time. In our model the combining sites for antigen and MHC are not independent as in classical dual-recognition models, but interact with each other by an allosteric mechanism. We envision a flexible receptor with combining sites for antigen and MHC that are capable of existing in a multitude of distinct complementarity states. MHC and antigen molecules act as allosteric effectors such that one ligand perturbs the conformation and therefore the specificity of the site for the other ligand. An essential feature of the model is that different MHC determinants induce different conformations at the anti-antigen site. In this way the receptor acquires multiple specificities. Within a particular complementarity state, precise recognition results from the requirement that antigen and MHC exhibit positive cooperativity in their binding to the T-cell receptor. Positive cooperativity is also the basis for MHC restriction. Reaction mechanisms are presented which describe the requirement that antigen and MHC both induce conformational changes in order to generate high-affinity binding to either ligand. As a precedent for the multistate allosteric receptor model, we discuss the properties of allosteric enzymes, especially ribonucleotide reductase, whose properties are analogous to those we have postulated for the T-cell receptor. Also discussed is the possibility that molecules such as Ly2, L3T4 and the Mls antigen, which have been found to play a role in antigen recognition, function as affinity-enhancing allosteric effectors that interact with the constant portion of the T-cell receptor.

The role of glycosylation in secretion and membrane expression of immunoglobulins M and A

The role of glycosylation in membrane expression and secretion of IgM and IgA was investigated in murine lymphoma and hybridoma cell lines, derived from I.29 tumor, which synthesize IgM or IgA with identical variable regions. Tunicamycin, a selective inhibitor of N-linked glycosylation, prevented the membrane expression of both isotypes, as demonstrated by immunofluorescence, radioiodination and endogenous labeling experiments. Selective immunoprecipitation and immunochemical analysis of membrane, intracellular and secreted molecules permitted us to determine the amount of membrane heavy chain externalized in the presence or absence of tunicamycin. Id 150 and Id 43, two I.29-derived hybridomas secreting IgA and IgM respectively, were differently affected by tunicamycin. While secretion of IgM was inhibited to greater than 95%, no inhibition of secretion of non-glycosylated IgA could be detected in Id 150 cells. These results indicate that different requirements for glycosylation exist in the biosynthetic pathways of immunoglobulin isotypes, and suggest that distinct intracellular transport systems may operate for membrane and secreted alpha-chains.

Integrity of glycoprotein complex sugars is required for homing but not for several other membrane-mediated functions

In order to correlate the biochemistry of cell surface carbohydrates with cell function, we have treated cells with swainsonine and followed the biochemical and functional modifications induced by this compound. After treatment with swainsonine, surface glycoproteins had a lower apparent molecular weight and a higher isoelectric point. This is compatible with the replacement of complex carbohydrates by hybrid or high-mannose carbohydrates. Several functional tests were unaffected. However, swainsonine-treated cells displayed an altered pattern of in vivo homing, suggesting that carbohydrates play a role in this process.

Wheat germ agglutinin-resistant variant of EL4 containing altered oligosaccharides as a target cell for cytotoxic T cells

A lectin-resistant variant of the murine EL4 lymphocytic leukemia cell line was selected in the presence of wheat germ agglutinin for low levels of cell-surface sialic acid. H-2Kb was the major internally radiolabeled H-2b molecule on the cell-surface of WD1, and it was not sialylated, as determined by two-dimensional gel analysis. Endo-beta-N-acetylglucosaminidase H treatment of the WD1 membrane fractions suggested that the oligosaccharides on the cell-surface H-2Kb molecule were complex, but nonsialylated. Monoclonal antibody inhibition of the allogeneically primed cell-mediated cytotoxicity (CMC) reaction indicated that the T cells (BALB/c anti-EL4; H-2d anti-H-2b) were specific only for the H-2Kb target cell antigen. These WD1 variant cells were used as targets in the CMC assay using anti-H-2Kb T cells and compared with the parent EL4 in vitro line. The change in the cell-surface oligosaccharide did not affect the susceptibility to lysis by the cytotoxic T lymphocytes even though there were 2.5-fold more H-2Kb antigens on the WD1 variant cell (1.5 X 10(5) sites/cell) than on the parent EL4 in vitro cell (5.9 X 10(4) sites/cell). It was possible to isolate highly purified preparations of H-2Kb from either the EL4 or the WD1 line using a monoclonal antibody affinity column. Interestingly, the variant WD1 cell would no longer grow in the peritoneal cavity of the syngeneic C57BL/6 mouse.

Cytolytic T-cell mediated lysis of reovirus-infected cells: requirements for infectious virus, viral particles, and viral proteins in infected target cells

The virological requirements for the recognition of infected target cells by cytolytic T lymphocytes (CTL), using reovirus, a nonenveloped, icosahedral virus has been investigated. Using mouse L cells infected at the nonpermissive temperature with ts (temperature-sensitive) mutants of reovirus in complementation groups C and G, it has been shown that the production of complete viral particles is not necessary for efficient lysis of infected cells by CTL. In addition, adsorption of purified viral particles and viral top component (TC), empty capsids lacking genome ds-RNA, to L cells just prior to use in cytolytic T cell assays is sufficient to produce target cells capable of being lysed, though target production is less efficient than with L cells infected with reovirus. Membrane fluorescence analysis of cells infected with reovirus ts mutants at the nonpermissive temperature and with adsorbed viral particles revealed the presence of the viral sigma 1 protein on the cell surface. For adsorbed particles, the degree of membrane fluorescence paralleled the capacity of CTL to lyse target cells. It is concluded that cells infected with icosahedral, nonenveloped viruses, like cells infected with enveloped viruses, express viral antigens on the cell surface even in the absence of the production of complete viral particles; adsorbed viral particles can be incorporated into the cell membrane in a manner sufficient for recognition and lysis by CTL, in the absence of actual infection of the cells.

The role of E receptors in the attachment of thymocytes and T lymphocytes to human target cells

Human thymocytes, activated T lymphocytes, and neuraminidase-treated T cells possess the distinct capacity of forming conjugates with various human cell lines. The present study investigated whether E receptors, which endow human T cells with their capacity to bind sheep red blood cells (SRBC), are involved in this phenomenon. Monoclonal antibodies to human T cells and various simple sugars were studied for their effect on the attachment of human T cells to target cells. A-22, a monoclonal antibody to the E receptor, inhibited the formation of E rosettes by T cells and SRBC, and reacted in immunofluorescent-staining assays with the majority of human thymocytes and peripheral T cells, and with T-cell lines capable of forming E rosettes. When human thymus cells were treated with A-22 antibody they showed a reduction of up to 70% in their capacity to attach to the GM-4762 lymphoblast cell line and the K-562 myeloid line. Antibody treatment of the target cells, rather than of the thymus cells, had no effect on the formation of conjugates between thymus cells and target cells. Treatment of thymus cells with various monoclonal antibodies to T cells which do not react with the E receptor had no inhibitory effect. The exposure of human thymus cells to various simple sugars (D-mannose, D-fucose, galactose, and lactose) markedly reduced their capacity of forming conjugates with target cells. Exposure of neuraminidase-treated peripheral blood lymphocytes and of activated T cells to A-22 antibody inhibited their attachment to human target cells. The present study suggests that E receptors play a role in the attachment of human thymus cells and activated T cells to other human cells, and raises the possibility that these T-cell receptors may be involved in the process of recognition of "self" structures by human T lymphocytes.

Expression of H-2 and viral antigens and resistance to the antitumor lysis of tunicamycin-treated MBL-2 lymphoma cells

The role of protein glycosylation in the tumor lysis mediated by effector cells derived from Moloney-sarcoma-virus(MSV)-immune mice was studied. Treatment of the Moloney-virus-induced H-2b lymphoma target cells, MBL-2, with tunicamycin (TM), an inhibitor of the protein-N-linked glycosilation, was found to cause a loss of susceptibility to lysis by MSV-immune syngeneic effectors cells, while the same target cells remained fully sensitive to the lytic action of anti-H-2b-immune lymphocytes. Examination of MBL-2 cell surface by lactoperoxidase, 125I iodination, and immunoprecipitation by antiviral protein sera revealed that env but not gag viral gene-encoded products were expressed on the surface of this lymphoma. The TM-induced alteration of cell surface expression of H-2Db, H-2Kb, and gp70 antigens was examined by a combined approach of serological and biochemical techniques. The results were concordant in indicating that (1) after 16 h of TM treatment the cells showed a decreased expression of the three glycoproteins, (2) H-2Db (the restriction element in this system) resulted more affected by the treatment than its counterpart H-2Kb (75% vs 50% reduction as compared to untreated cells), (3) an additional lighter form of H-2Kb was found on the surface of TM-treated cells. In the context of an "associative recognition' of Db and gp70 by MSV-immune effector cells, our results may explain the loss of susceptibility to antitumor effectors of TM-treated MBL-2 cells by a quantitative reduction in the expression of both molecules which interact to create the target structure of syngeneic effectors.

Inhibition of glycosylation prevents H-2K and D antigen expression on SV40 virus-transformed cells

Tunicamycin, an inhibitor of glycosylation, was used to examine the role of carbohydrate moieties of glycoproteins involved in recognition of Simian virus 40 (SV40)-transformed cells by cytotoxic T lymphocytes (CTL). Tunicamycin treatment renders such cells refractory to lysis by H-2 restricted, SV40-specific CTL as well as by allogeneic CTL directed only against H-2 antigens. Treated cells are no longer susceptible to lysis by anti-H-2 antisera and complement, nor are they stained by monoclonal anti-H-2 antibodies in an indirect immunofluorescence assay. No accumulation of H-2 proteins was detected in immunoprecipitates from cells labeled with [35S]methionine in the presence of tunicamycin. It is concluded that tunicamycin prevents the expression of H-2 glycoproteins in these cells, perhaps due to accelerated degradation of the unglycosylated molecules.

Cross-reactive, cell-associated antigen on L929 cells infected with temperature-sensitive mutants of sindbis virus

Temperature-sensitive (ts) mutants of Sindbis virus (SIN) were used to aid in the identification of alphavirus cross-reactive proteins on the surface of infected cells by antibody-dependent, complement-mediated cytolysis. Antisera prepared in rabbits against purified SIN or Semliki Forest viruses were highly cytotoxic for cells infected with wild-type SIN and for cells infected at the permissive temperature with maturation-defective, ts mutants of SIN belonging to several distinct complementation groups. When these SIN mutants were analyzed by antibody-dependent, complement-mediated cytolysis at the restrictive temperature only cells infected with the SIN mutant of complementation group E, ts20, participated in both homologous (with anti-SIN serum) and heterologous (with anti-Semliki Forest virus serum) antibody-dependent, complement-mediated cytolysis reactions. These data and the known defect of ts20 suggested that the cell-associated viral E1 glycoprotein was a functional target antigen for homologous and cross-immunoreactivity in alphavirus-infected cells. At the restrictive temperature there were quantitative differences in antibody-dependent, complement-mediated cytolysis reactivity of ts20- versus wild type-infected cells consistent with the suggestion that ts20-infected cells do not fully express all of the homologous or the cross-reactive antigenic determinants found in wild-type infection. Additional potential sites for antigenic determinants involved in alphavirus-immune cross-reactivity are discussed in relation to events in virus maturation.