Expression of HLA-DR antigens at the surface of mouse L cells co-transfected with cloned human genes

Understanding the mechanism of action of bacterial superantigens from a decade of research

In the face of the unique diversity and plasticity of the immune system pathogenic organisms have developed multiple mechanisms in adaptation to their hosts, including the expression of a particular class of molecules called superantigens. Bacterial superantigens are the most potent stimulators of T cells. The functional consequences of the expression of superantigens by bacteria can be extended not only to T lymphocytes, but also to B lymphocytes and to cells of the myeloid compartment, including antigen-presenting cells and phagocytes. The biological effects of bacterial superantigens as well as their molecular aspects have now been studied for a decade. Although there is still a long way to go to clearly understand the role these molecules play in the establishment of disease, recently acquired knowledge of their biochemistry now offers unique experimental opportunities in defining the molecular rules of T-cell activation. Here, we present some of the most recent functional and molecular aspects of the interaction of bacterial superantigens with MHC class II molecules and the T-cell receptor.

Conserved structural features between HLA-DO beta and -DR beta

HLA-DO is a non-classical MHC class II molecule presumed to play a specialized role in the antigen processing pathway. We have modeled the HLA-DO beta-chain and found its overall structure compatible with the one of DR beta. Functional studies further highlighted the similarity between these beta-chains of the class II family of proteins. Indeed, a mixed heterodimer composed of the DR alpha and a chimeric DO beta-chains presented bacterial superantigens to T cells and was shown to interact with CD4. The implications of such structural conservation for the in vivo functions of HLA-DO are discussed.

Defective intracellular transport as a common mechanism limiting expression of inappropriately paired class II major histocompatibility complex alpha/beta chains

Distinct combinations of class II major histocompatibility complex (MHC) alpha and beta chains show widely varying efficiencies of cell surface expression in transfected cells. Previous studies have analyzed the regions of the class II chains that are critically involved in this phenomenon of variable expression and have shown a predominant effect of the NH2-terminal domains comprising the peptide-binding site. The present experiments attempt to identify the post-translational defects responsible for this variation in surface class II molecule expression for both interisotypic alpha/beta combinations failing to give rise to any detectable cell membrane molecules (e.g., E alpha A beta k) and intraisotypic pairs with inefficient surface expression (e.g., A alpha d A beta k). The results of metabolic labeling and immunoprecipitation experiments using L cell transfectants demonstrate that in both of these cases, the alpha and beta chains form substantial amounts of stable intracellular dimers. However, the isotype- and allele-mismatched combinations do not show the typical post-translational increases in molecular weight that accompany maturation of the N-linked glycans of class II MHC molecules. Studies with endoglycosidase H reveal that no or little progression to endoglycosidase H resistance occurs for these mismatched dimers. These data are consistent with active or passive retention of relatively stable and long-lived mismatched dimers in a pre-medial-Golgi compartment, possibly in the endoplasmic reticulum itself. This retention accounts for the absent or poor surface expression of these alpha/beta combinations, and suggests that conformational effects of the mismatching in the NH2-terminal domain results in a failure of class II molecules to undergo efficient intracellular transport.

The generation and characterization of human monocyte hybridomas

Fusion of interferon-gamma activated peripheral blood monocytes to a mutagenized hypoxanthine-guanine phosphoribosyltransferase (HGPRT)-deficient U937 parent line was performed resulting in the generation of a series of unique cloned monocyte hybridomas. These cell lines were proven to be true hybrids by the acquisition of donor class I antigens as well as other donor derived chromosomes. In addition, novel functional characteristics were observed including secretion of specific monokines and the acquisition of phagocytic capabilities. The ability to generate immortalized human monocyte hybridomas will allow for more in depth analysis of monocyte subpopulations and dissection of specific monocyte functions.

An in vitro model of peptide-mediated immunomodulation of the human T cell response to Dermatophagoides spp (house dust mite)

Allergic sensitivity of Dermatophagoides spp (house dust mites) is mediated by specific IgE antibody, the production of which requires the presence of CD4+ helper T cells. Attempts to hyposensitize this response in allergic individuals have depended on the administration of extracts of specific allergen. However, the ability of peptides derived from unrelated antigens to inhibit specific immune responses offers an alternative approach to therapy. We have addressed this question by examining the ability of a nonstimulatory peptide analogue derived from influenza virus hemagglutinin to modulate T cell recognition of house dust mite. The peptide inhibited the response of mite-specific CD4+ T cell clones restricted by either the HLA-DRAB1 or DRAB3 gene products. Furthermore, mite-induced polyclonal T cell responses were negatively modulated by the peptide, whereas recognition of common recall antigens remained intact. The inhibitory effects were mediated at the level of the antigen-presenting cell, since no inhibition of mitogen or anti-CD3 antibody-driven T cell proliferation was observed. In direct binding assays, the peptide analogue bound to selected HLA-DR molecules expressed on the membrane of antigen-presenting cells, with specificity predominantly for those class II proteins capable of restricting house dust mite-allergen T cell recognition.

HLA antigens in ocular tissues. III. Antigen presentation by gamma interferon-treated cultured uveal cells

In previous studies we have shown that normal human uveal cells, with the exception of vascular endothelium, do not express class I or class II HLA antigens in vivo. Class I antigens are induced in vitro by a variety of cytokines, while class II antigens are only induced by gamma interferon. In this study we examine the capacity of cultured uveal cells, rendered class II HLA antigen positive by gamma interferon, to present antigen to T cells. Cultured uveal cells were found to present antigen (tetanus toxoid, PPD, and Candida albicans) to T cells, but only when they were pretreated with gamma interferon. This function of uveal cells was antigen specific and MHC restricted and was blocked by class II-specific monoclonal antibodies, indicating the crucial role of class II HLA antigens in antigen presentation.

B-cell-specific enhancer activity of conserved upstream elements of the class II major histocompatibility complex DQB gene

A 95-base-pair immediate upstream sequence of the human class II major histocompatibility complex DQB gene containing the conserved X and Y elements showed enhancer activity in a transient expression assay. An "enhancer test plasmid" harboring the bacterial chloramphenicol acetyltransferase gene under the control of a truncated simian virus 40 enhancerless early promoter was employed. The DQB sequence inserted into this plasmid was active as an enhancer in Raji cells (human Burkitt lymphoma cells) but not active in Jurkat cells (human T-cell leukemia cells) or in HeLa cells (human cervical carcinoma cells). This cell-type specificity suggests that this enhancer activity may be involved in the tissue specificity of the DQB gene that is normally expressed only in mature B cells, macrophages, and thymic epithelial cells. Deletion analysis showed that both X and Y box sequences are essential for the full activity of the enhancer sequence and that these two sequences may function in a cooperative manner as cis-acting elements. Further deletions were used to define the 5' border of the X element. These results suggest that previously characterized protein factors that bind to X and Y include transcription factors involved in the cell-type specificity of this enhancer activity.

Serological recognition of HLA-DR allodeterminant corresponding to DNA sequence involved in gene conversion

HLA class II molecules were isolated from mouse L cells transfected with a DR alpha gene and an allele, 52a, of locus DR beta III from an HLA-homozygous cell line, AVL, of the DR3 haplotype. The isolated molecules were found to possess a new allospecificity, named TR81. This specificity behaved allelic to the previously described specificity TR22 encoded by another allele, 52b, of the DR beta III locus. The TR81 specificity was also present on the DR beta I gene product of the DR3 haplotype. The nucleotide sequence of the gene encoding TR81 differs from TR81-negative DR beta genes of the DRw52 family in only two codons, both located in the regions known to be involved in a gene conversion event. Consequently, the following conclusions can be formulated. (a) TR81 is a bi-locus specificity and allelic to TR22 only in its DR beta III locus localization. (b) The TR81 specificity is the phenotypic counterpart of the gene conversion event which led to the generation of the DR beta I gene of the DR3 haplotype. (c) One or both individual amino acid substitutions in the first domain of the DR beta chain are responsible for the TR81 allospecificity. (d) Since TR81 is expressed on the DR beta I chain of the DR3 haplotype, it is possible that TR81 and DR3 represent the same serological specificity.

Antigen presentation to HLA class II-restricted measles virus-specific T-cell clones can occur in the absence of the invariant chain

A human fibroblast line expressing HLA-DR1 antigen on its surface was generated by transfection with DR alpha and DR beta cDNAs. Expression of the invariant chain gene was not detectable in the transfected fibroblasts and was not induced by infection with measles virus. Lysis of measles virus-infected cells occurred with DR1- but not with DR4-restricted measles virus-specific cytotoxic T-lymphocyte (CTL) clones and was inhibited by a monoclonal antibody specific for DR antigen. Therefore, the invariant chain is not required for DR-restricted presentation of measles virus antigens by this fibroblast line. Transfected fibroblasts were lysed as efficiently as an autologous B-cell line even though they expressed much less surface DR antigen. Lysis of both the transfected fibroblasts and the B-cell line was insensitive to treatment with chloroquine. These results demonstrate that expression of a DR alpha beta heterodimer at the surface of this fibroblast line is necessary and sufficient for presentation of measles virus antigens to specific CTL clones.

Characterization of N-linked oligosaccharides of an HLA-DR molecule expressed in different cell lines

In order to determine the factors that influence the glycosylation of an integral membrane protein, we investigated the N-glycosylation of a molecule of the human major histocompatibility complex (MHC) class II, the HLA-DR antigen. This glycoprotein was studied in a human Epstein-Barr-virus-transformed B cell line and in a mouse fibroblastic cell line co-transfected with DR alpha and DR beta genes. We observed that the HLA-DR-antigen glycosylation pattern depends on the cell line in which processing takes place and is closely related to the glycosylation pattern of the overall cellular glycoproteins. Furthermore, when comparing the glycosylation of the separated alpha- and beta-chains, differences were noticed within the same molecule, showing the importance of the individual peptide backbone for the glycosylation process.

Structure and expression of HLA-DQ alpha and -DX alpha genes: interallelic alternate splicing of the HLA-DQ alpha gene and functional splicing of the HLA-DQ alpha gene using a retroviral vector

The nucleotide sequences of the two closely related HLA-DQ alpha and HLA-DX alpha genes have been determined. Exons coding for the signal peptide, alpha 2 and transmembrane domains are 94-99% homologous, whereas the alpha 1 exon and the promoter region have diverged as much as or more than introns and the 3' untranslated region. The promoter regions of both genes contain two short sequences thought to be important for regulation of transcription by gamma-interferon. Transfection studies established that the DQ alpha and DQ beta genes encode the HLA-DQ antigen. Transcripts of varying length are produced from different alleles as the result of the use of alternate splice and polyadenylation signals at the 3' end of the DQ alpha gene. Thus typing at the DQ alpha locus can be achieved by Northern blot analysis. No transcript of DX alpha was detected in B lymphocytes. The DX alpha gene was accurately spliced when introduced into a retroviral vector, suggesting that the lack of expression of DX alpha is not due to aberrant splice signals.

Immunochemistry of the HLA class II molecules isolated from a mouse cell transfected with DQ alpha and beta genes from a DR4 haplotype

Cells from a mouse B lymphoma were transfected by DQ alpha and DQ beta genes derived from a DR4 haplotype. Quantitatively, the resulting expression of human class II molecules was similar to that of human B lymphoblastoid cell lines. Qualitatively, the transformant class II molecules differed from "normal" class II molecules in their carbohydrate moiety. As for their antigenic specificity, they were shown to carry two determinants previously identified on DQ molecules controlled by DR4 haplotypes, i.e., DQw3 and DCHON. The transformant molecules did not carry a third DR4-associated specificity, DC5 (equivalent to TA10), and must possess a structure allelic to DC5. However, no corresponding alloantigenic specificity was detected by a screening of relevant alloantisera.

The role of transfected HLA-DQ genes in the mixed lymphocyte reaction-like condition

DR gene products are commonly thought to be involved in the induction of the mixed lymphocyte reaction (MLR). However, very little is known about the role of HLA-DQ antigens in the MLR. To address this question, we introduced DQ alpha and beta chain genes into mouse L cells, a human T-cell line, and a human premonocytoid cell line using a liposome-mediated transfer technique. The DQ alpha and DQ beta genomic clones were isolated from a DR2 DQw1 and a DR3 DQw2 phage library, respectively. The pSV2-Neo gene was introduced as a selection marker with both DQ alpha and DQ beta. The resultant transfected cells were able to bind several HLA class II monoclonal antibodies. In addition, these cells were found to be efficient in stimulating peripheral blood lymphocyte proliferation under MLR-like conditions, implying a role for HLA-DQ molecules in HLA-D typing differences.

Immunochemical analysis of a cell transfected with an HLA-DR gene reveals a new alloantigenic specificity within HLA-DRw52

The HLA-DR antigen has been prepared from the surface of a mouse fibroblast cell line transfected with a single HLA-DR beta-chain gene as well as single HLA-DR alpha and invariant chain gene. Since the HLA-DR beta chain gene studied corresponds to the DR beta III locus, the DR serological specificities detected on the transformed cells can be assigned to this locus. The use of the HLA-DR-producing mouse cell line has led to the identification of a new serological specificity included within DRw52 and associated with some DR3, some DRw6 and all DR5 haplotypes studied. Most likely this new specificity corresponds to an allelic polymorphism at the DR beta III locus of DRw52 individuals and can serve as a new serological marker for this subset of DR3, DR5 and DRw6 haplotypes.

Unexpected expression of a unique mixed-isotype class II MHC molecule by transfected L-cells

Class II (Ia) major histocompatibility complex (MHC) molecules are heterodimeric integral membrane proteins composed of non-covalently linked alpha and beta glycoprotein chains. Studies of both normal cells and L-cell transfectants have shown that neither alpha- nor beta-chains are found on the cell surface alone, and that alpha beta dimers are required for membrane expression. In both mouse and man, several distinct non-allelic alpha and beta genes exist. Analysis of Ia molecules by immunoprecipitation and two-dimensional gel electrophoresis has demonstrated apparently selective association of particular pairs of the various alpha- and beta-chains to form the expressed class II isotypes I-A and I-E (mouse) or DQ, DP and DR (human). Because the various alpha- or beta-chains encoded by distinct loci exist in many allelic forms within a species, such specific pairing suggests a special role for isotypically conserved regions of each chain in the association process. In attempting to localize such putative assembly-controlling regions using the technique of DNA-mediated gene transfer, various combinations of murine alpha and beta genes were introduced into L-cells. Here we report the unexpected observation, following transfection, of mixed-isotype (Ad beta Ea/k alpha) molecules on the L-cell membrane and document that the formation of this pair is strongly influenced by allelic polymorphism of the A beta chain.

Linkage map of three HLA-DR beta-chain genes: evidence for a recent duplication event

The predominant class II, or Ia, antigen of the human major histocompatibility complex is HLA-DR. It consists of an alpha and a beta chain, the latter being responsible for the remarkable polymorphism of these Ia antigens. Studies with cloned genes had shown the existence of more than one DR beta-chain locus. We have isolated about 100 kilobases of the HLA-DR beta-chain gene region from a cosmid library generated from a consanguineous homozygous B-cell line of the DR3 haplotype. Three HLA-DR beta-chain genes have been characterized. They are arranged in a head-to-tail orientation. One of the genes lacks the region encoding the first domain of the DR beta chain. The two other genes are transcribed, as shown by RNA blot hybridization analysis. A striking restriction site homology has been found within the DR beta-chain gene cluster, suggesting a recent duplication event involving at least 25 kilobases of DNA. Moreover, the molecular map of DR beta chain genes cloned from B-cell lines of two other HLA-DR haplotypes shows extensive homology between alleles of a given DR beta-chain locus.

L3T4 but not LFA-1 participates in antigen presentation by Ak-positive L-cell transformants

We report that mouse L cells expressing Ak class II molecules on their surface after DNA-mediated gene transfer are capable of presenting the synthetic copolymer (Glu60 Ala30 Tyr10) to Ak-restricted long-term T-cell clones. Antigen-induced T-cell stimulation could be inhibited by monoclonal antibodies (mAb) directed at spatially distinct determinants of the alpha and/or beta subunits of the Ak molecule, and by the rat L3T4-specific mAb H129.19. In contrast, several rat mAb reactive with the mouse LFA-1 molecule failed to inhibit T-cell activation when L cells were used as antigen-presenting cells (APC), although these mAb strongly inhibited the same T-cell responses in the presence of leukocytic APC. Similarly, the cytolytic activity of the Ak-specific T-cell clone A15.1.17 was blocked by L3T4-specific and by LFA-1-specific mAb when tested on Ak-positive B-cell hybridomas, but only by L3T4-specific mAb and not by LFA-1-specific mAb when Ak-positive L-cell transformants were used as targets. These data support the notion that the LFA-1 molecule is not necessary for T-cell activation, and suggest that its functional role as an accessory molecule depends on the leukocytic nature of the APC tested.

Ia-transfected L-cell fibroblasts present a lysozyme peptide but not the native protein to lysozyme-specific T cells

We studied the antigen-presenting capacity of mouse L fibroblasts transfected with genes encoding Ia polypeptides of the major histocompatibility complex (MHC). These cells function as efficient antigen-presenting cells (APC) in stimulating peptide antigen-specific MHC-restricted proliferation of long-term T-cell lines, thus establishing the capacity of Ia-expressing L-cell transfectants to present antigens to apparently normal T cells. However, in contrast to splenic APC, L-cell transfectants fail to present native hen egg-white lysozyme to the same T cells. Since this result is similar to that obtained with physiologic APC pretreated to prevent antigen degradation, it suggests that L-cell transfectants, without such pretreatments, may be compromised in their ability to process native lysozyme. However, since such transfectant cells have been shown to present other complex polypeptides such as keyhole limpet hemocyanin, a random copolymer of glutamic acid, alanine, and tyrosine, and influenza virus neuraminidase, this observation suggests that protein antigens differ in the stringency of processing requirements.

Major histocompatibility complex regulation of the immune response

The ability of an organism to distinguish self from nonself is determined by a cluster of genes located in the major histocompatibility complex. Recent advances in molecular genetics and cellular immunology have begun to elucidate the mechanisms responsible for immune response regulation. In this review article, the genetic organization of the murine and human major histocompatibility complexes and the manner by which their gene products modulate immune responsiveness are discussed.

Functional expression of a microinjected Ed alpha gene in C57BL/6 transgenic mice

The class II major histocompatibility antigens, I-A and I-E, have been detected on the surface of certain immunocompetent cells, including B lymphocytes and monocytes. These molecules are involved in cell-cell interactions in the immune responses. Each class II antigen consists of two subunits, alpha and beta chains, and the genes encoding these subunits have been well characterized at the molecular level. To analyse the regulatory mechanism of E alpha gene expression and the role of the I-E antigen in the regulation of the immune responses, we have produced transgenic mice by microinjecting cloned Ed alpha genes into fertilized eggs of C57BL/6 mice of b haplotype. This strain of mouse carries a deletion in the upstream (5') region of the E alpha gene covering the transcriptional promoter and, therefore, does not express this gene. Interestingly, this genetic defect of the E alpha gene is accompanied by the inability of the host mouse to respond to a certain set of antigens, phenomena generally termed Ir gene control. We report here that the Ed alpha genes are expressed in these transgenic mice to form the I-Ed alpha Eb beta antigen on the surface of B lymphocytes and monocytes and that these I-E antigens are functional in terms of the induction of a mixed lymphocyte reaction and the restoration of immune responsiveness to poly(L-glutamic acid-L-lysine-L-phenylalanine) (GL-Phe).

Genetic complexity and expression of human class II histocompatibility antigens

The genes encoding nearly all of the serologically defined class II antigens of the major histocompatibility complex have been isolated. Three class II loci have been studied in great detail. The DR region contains a single alpha gene and 3 beta chain genes, 1 of which is a pseudogene. The DR alpha chain gene has been linked to a DR beta gene which encodes a beta protein which contains the serological determinant MT3. A second cosmid cluster contains 2 beta genes, 1 of which encodes the DR4 allospecificity. The identification of these genes has been made by the comparison of amino terminal sequences of DR molecules obtained from a DR4 cell line and the deduced protein sequences of the beta 1 exons from cosmid and phage clones. A conserved element including the promoter and signal sequence is found at the 5' end of each of the 3 DR beta genes. Additionally, this element occurs three more times in the DR region, raising the question of whether additional beta chain genes might be found. The DQ region contains 2 pairs of genes, 1 of which encodes the DQ antigen. The 2nd pair of genes, called DX alpha and beta, appears to be capable of expressing a DQ-related product, although, to date, there is no evidence for its expression. The DP region also contains 2 pairs of genes. One pair encodes the DP antigen while the 2nd alpha-beta pair is shown to be composed of pseudogenes. The location of polymorphic regions in these genes and aspects of their relationship to the serology, evolution, and function of the class II MHC are discussed. The control of expression of class II genes by gamma-interferon has been examined. The promoters of class II genes are characterized by two conserved sequences common to all alpha and beta chain genes as well as by conserved sequences specific for either alpha or beta chain genes. In addition to studies of expression by DNA-mediated gene transformation, a system for the gene transfer of MHC antigens utilizing transmissible retrovirus vectors is described. Retrovirus vectors have been used to transmit DR alpha, DR beta, and the invariant chain (gamma) sequences to recipient cells with resultant expression of these proteins.

Serological and immunochemical analysis of the products of a single HLA DR-alpha and DR-beta chain gene expressed in a mouse cell line after DNA-mediated cotransformation reveals that the beta chain carries a known supertypic specificity

Using a mouse cell line transformed with and expressing a single HLA DR-alpha and DR-beta chain gene, we present evidence that the product of the DR-beta chain gene carries a supertypic determinant, BR3, previously defined by serology. The amino acid sequence of this beta chain gene is determined from the DNA sequence. Another DR-associated supertypic specificity defined by monoclonal antibody MCS7 was not encoded by this DR-beta chain gene. This provides formal proof that a supertypic specificity can be associated with a product of a distinct DR-beta locus. We propose that haplotypes sharing such specificities are evolutionarily related.

SB subregion of the human major histocompatibility complex: gene organization, allelic polymorphism and expression in transformed cells

The SB region of the human major histocompatibility complex (MHC) has been cloned from cosmid and lambda phage libraries made from the human B-lymphoblastoid cell line Priess (DR4/4, DC4/4, SB3/4). Two alpha genes and two beta genes are encoded in the 100 kb long SB region in the order SB alpha-SB beta-SX alpha-SX beta. The SB alpha and SB beta genes encode the alpha and beta subunits of the SB subset of class II MHC molecules. Both the SX alpha and the SX beta genes are pseudogenes in the haplotype examined. From the isolated clones, the two haplotypes of the Priess cell line, SB3 and SB4, are distinguished by nucleotide sequencing and blot hybridization analyses. Restriction site polymorphisms between the SB3 and SB4 clones were observed only in relatively small regions of the SB beta and SX beta genes. A mouse macrophage cell line was transfected with one of the cosmid clones containing both SB alpha and SB beta genes. Expression of the alpha and beta genes was detected by fluorescene-activated cell sorting (FACS) and two-dimensional gel electrophoresis using SB-specific monoclonal antibodies.

Functional expression of HLA-DP genes transfected into mouse fibroblasts

The HLA class II antigens are a highly polymorphic family of dimeric cell-surface glycoproteins, expressed predominantly on the surface of immunocompetent cells. They are intimately involved with the induction of the T-cell response to extrinsic antigen and are important predisposing factors for a wide spectrum of autoimmune diseases. We describe here the expression of a class II product from the HLA-DP (new WHO nomenclature, formerly SB) subregion after transfer of cloned genes into mouse fibroblasts. The transfected DP antigen is recognized by several HLA class II monoclonal antibodies and, though present in a mouse cell background, is able to function in the presentation of influenza antigen to cloned DP-restricted human T lymphocytes.

Membrane Ia expression and antigen-presenting accessory cell function of L cells transfected with class II major histocompatibility complex genes

To study the relationship between the structure and function of Ia antigens, as well as the physiologic requirements for antigen presentation to major histocompatibility complex-restricted T cells, class II A alpha and A beta genes from the k and d haplotypes were transfected into Ltk- fibroblasts using the calcium phosphate coprecipitation technique. Individually transfected genes were actively transcribed in the L cells without covalent linkage to, or cotransformation with, viral enhancer sequences. However, cell surface expression of detectable I-A required the presence of transfected A alpha dA beta d or A alpha kA beta k pairs in a single cell. The level of I-A expression under these conditions was 1/5-1/10 that of Ia+ B lymphoma cells, or B lymphoma cells expressing transfected class II genes. These I-A-expressing transfectants were tested for accessory cell function and shown to present polypeptide and complex protein antigens to T cell clones and hybridomas in the context of the transfected gene products. One T cell clone, restricted to I-Ak plus GAT (L-glutamic acid60-L-alanine30-L-tyrosine10), had a profound cytotoxic effect on I-Ak- but not I-Ad-expressing transfectants in the presence of specific antigen. Assays of unprimed T cells showed that both Ia+ and Ia- L cells could serve as accessory cells for concanavalin A-induced proliferative responses. These data indicate that L cells can transcribe, translate, and express transfected class II genes and that such I-A-bearing L cells possess the necessary metabolic mechanisms for presenting these antigens to T lymphocytes in the context of their I-A molecules.

Molecular organization of the HLA-SB region of the human major histocompatibility complex and evidence for two SB beta-chain genes

The class II products of the major histocompatibility complex, also called Ia antigens, are composed of two polypeptide chains, the alpha and beta chains, both encoded within the major histocompatibility complex. In man, the class II antigens can be divided into three biochemically distinct groups called HLA-DR, HLA-DC, and HLA-SB. Our isolation of cDNA clones for the polymorphic beta chain of HLA-DR and HLA-DC has allowed us to study the organization of the class II genes. Here we identify the HLA-SB beta-chain gene in recombinant clones from a cosmid library generated from a consanguineous homozygous B-cell line. The SB beta-chain gene is linked to the SB alpha-chain gene and the two genes are in opposite orientation. A second SB beta-chain gene, corresponding to a new SB beta II locus, has also been identified and cloned. The SB beta-chain genes show much less allelic restriction site polymorphism than the genes for the beta chains of HLA-DR or HLA-DC.

The complete sequence of the mRNA for the HLA-DR-associated invariant chain reveals a polypeptide with an unusual transmembrane polarity

A non-polymorphic polypeptide is associated intracellularly with the alpha and beta chains of murine Ia antigens and of human HLA-DR antigens. The exact role and the structure of this invariant chain have not been determined so far. A cDNA clone encoding the 33 000 dalton human invariant chain has been isolated. The nucleotide sequence of a near full-length cDNA clone, together with the sequence of the 5' portion of the mRNA determined by primer-extension, are reported here. The protein structure deduced from that sequence shows an unusual feature: the presence of a hydrophobic transmembrane region near the NH2 terminus, and of two glycosylation sites near the middle, indicates that the invariant chain has a polarity of membrane insertion which is inverted relative to histocompatibility antigens and most transmembrane proteins.

Functional expression of a cloned I-A beta k gene in B-lymphoma cells

The immune response genes of the mouse encode two cell-surface glycoproteins, I-A and I-E, that play critical roles in determining the animal's immune responsiveness. The I-A antigen contains two chains, alpha and beta. A cloned beta-chain gene, I-A beta k, was introduced into B-lymphoma cells that express I-Ad. The transfected gene was successfully expressed on the cell surface of the recipient cells and was functional in stimulating allospecific T cells.

Gene transfer of H-2 class II genes: antigen presentation by mouse fibroblast and hamster B-cell lines

We have transferred the mouse Ak alpha and Ak beta genes, which encode the class II I-Ak molecule, into mouse L-cell fibroblasts and hamster B cells. I-Ak molecules are expressed on the surface of both cell types. The L-cell and hamster B-cell I-Ak molecules appear normal by serological analyses and two-dimensional gel electrophoresis. Furthermore, the I-Ak molecules on L cells can act as targets for the allogenic T-cell killing of the transformed L cells. The I-Ak molecules in both mouse fibroblasts and hamster B cells can present certain antigens to T-cell helper hybridomas. Thus only class II molecules are required to convert the nonantigen-presenting cell. Accordingly, it will be possible to dissect the structure-function relationships existing between Ia molecules, foreign antigen, and T-cell receptor molecules by in vitro site-directed mutagenesis and gene transfer.

Organization of the transcriptional unit of a human class II histocompatibility antigen: HLA-DR heavy chain

A total of 5724 base pairs of a recombinant phage DNA containing a human HLA-DR heavy chain gene including flanking regions has been analyzed. The regions corresponding to all the exons have been identified. The sites of initiation of transcription and polyadenylation have been determined. A large intron of 2399 base pairs separates the first exon containing the 5' untranslated region and the signal peptide from the second exon containing the N-terminal peptide domain.

Genes of the major histocompatibility complex in mouse and man

The genes of the major histocompatibility complex code for cell-surface molecules that play an important role in the generation of the immune response. These genes and molecules have been studied intensively over the last five decades by geneticists, biochemists, and immunologists, but only recently has the isolation of the genes by molecular biologists facilitated their precise characterization. Many surprising findings have been made concerning their structure, multiplicity, organization, function, and evolution.

Functional expression of a transfected murine class II MHC gene

The activation of T helper lymphocytes involves the recognition of class II major histocompatibility complex antigens, which are dimeric glycoproteins (of subunit composition A alpha A beta or E alpha E beta) expressed on the surfaces of macrophages and B lymphocytes. One approach to understanding the relationship between the structure of these antigens and their functions in the immune response is to clone the genes that encode them, to obtain functional expression of the cloned genes transfected into an appropriate cell line, and then to see how those functions are affected in variant genes generated in vitro. We report here the expression in Iad-bearing B cells of an Ak beta gene, which confers on the transfected cells the capacity for both allostimulation and antigen-dependent activation of an I-Ak-restricted T-cell clone.

Isolation of cDNA clones for the p33 invariant chain associated with HLA-DR antigens

HLA-DR antigens are polymorphic cell surface glycoproteins involved in the control of the immune response in man. They consist of two subunits, the alpha and the beta chains. In addition, an invariant glycoprotein of Mr 33,000 (DRp33) is associated intracellularly with HLA-DR antigens. A cDNA clone for DRp33, called 33-10, was isolated. Because no amino acid sequence has yet been determined for DRp33 the identification of cDNA clone 33-10 was based on selection of mRNA by hybridization, subsequent translation in a rabbit reticulocyte lysate supplemented with microsomes, and translation in microinjected Xenopus oocytes followed by immunoprecipitation with an anti-DR antiserum. The translation products assembled with DR alpha and beta chains in oocytes coinjected with all three mRNAs. Assembly of DR alpha and beta chains was also observed in the absence of DRp33 mRNA. Furthermore, when compared with DRp33 immunoprecipitated from a human B-cell line, translation products of the hybrid-selected mRNA showed (i) identical migration in two-dimensional gel electrophoresis, (ii) identical apparent molecular weight in the absence of N-linked glycosylation, and (iii) a very similar two-dimensional peptide map. Transcription of the DRp33 gene into a mRNA 1,400 nucleotides long was observed in B cells but was undetectable in T-cell lines and was very low in liver. Thus, DRp33 appears to be coordinately expressed with DR alpha and beta chains. Hybridization to DNA of mouse-human somatic cell hybrids showed that DRp33 is encoded by a gene that is located outside the major histocompatibility complex.