The gene encoding the human class II antigen-associated gamma chain is located on chromosome 5

A possible role of the MHC-associated invariant chain in rheumatoid arthritis

Antigen presentation to T-helper (Th) cells by MHC class II proteins is an important event in the initiation and/or maintenance of autoimmune disease. The class II proteins have a wide, degenerate specificity and are capable of binding several different peptides, including self-peptides. However, recent data suggest that a protein called invariant chain, Ii, binds to the class II molecule in the endoplasmic reticulum in such a way that precludes the binding of peptides derived from intracellular self- or non-self-proteins. The class II-Ii complex is transported through the endoplasmic reticulum to the endosomes, which contain peptides derived from extracellular proteins. The acidic pH and proteolysis in the endosomes cause dissociation of the class II-Ii complex, making the class II protein available for binding to the peptides. Thus, the Ii chain appears to play an important role in suppressing autoimmune responses. A hypothesis that a defect in the Ii chain could lead to autoimmune disorders is proposed. These defects would include alterations in the Ii chain such that it is no longer able to compete with the self-peptides for binding to the class II protein.

Interferon-γ response region in the promoter of the class II MHC gene, DPA

The class II MHC gene DPA is inducible by interferon-gamma (IFN-gamma), whereas the DQB gene is not inducible in most cell types. To investigate the DNA region specifically responsible for inducibility or its lack that may be required (in addition to the elements required for constitutive expression of class II genes), hybrid promoters were constructed between the proximal 5' regions of the DPA promoter up to -148 bp, which is IFN-gamma inducible, and of the DQB promoter up to -160 bp, which is not inducible. As a result of these and previous studies [9, 10], the region of the DPA gene required for its IFN-gamma inducibility was localized to 27 bp between -55 and -81, including the Y-box element and its flanking nucleotides.

HLA and disease

Many human diseases are associated with HLA class I, class II and class III antigens. It appears that the class III antigen disease associations can be explained by a direct defect operating at the level of either the class III gene or its gene product. The mechanism underlying class I and class II antigen disease associations is at present unknown. In this review we have considered thirty diseases which have been ranked according to their relative risk as defined by the frequency of a given HLA antigen in patient and control populations. The chronic inflammatory disorder, ankylosing spondylitis and its association with HLA B27 has been used as a model to study the HLA linked diseases. We have suggested that the disease may be caused by the Gram-negative microorganism Klebsiella which has antigenic similarity to HLA B27. It is proposed that some antibodies made against Klebsiella bind to HLA B27, thereby acting as autoantibodies leading to the pathological sequelae of chronic inflammatory arthritis. This is the crosstolerance hypothesis or molecular mimicry model and it has been compared to the receptor model. It is further suggested that the crosstolerance hypothesis can be utilised as a general theory to explain the association of other diseases with the class I and class II antigens, and offer a possible explanation for the polymorphism of HLA.

Chronic multifocal osteomyelitis, a new recessive mutation on chromosome 18 of the mouse

Mice with tail kinks and deformities in their lower extremities were observed in a litter of C.D2-Qa-2+N6F15 mice. A mutant line that exhibits this phenotype in 100% of its offspring was established by subsequent breeding. The abnormalities resembled to some degree those found in a human syndrome termed chronic recurrent multifocal osteomyelitis (CRMO). Accordingly, we name the new mutation chronic multifocal osteomyelitis (cmo). Breeding analysis showed that the defect was determined by a single autosomal recessive gene. Restriction fragment length polymorphism (RFLP) analysis of progeny from a backcross between Mus musculus domesticus (CLA) and C.D2-Qa-(2+)-cmo/cmo indicated that the cmo gene resides on mouse Chromosome 18.

Molecular profiles of the cell membrane bound and cytoplasmic forms of the human MHC class-II associated invariant polypeptides

Several sub-types of histocompatibility class-II molecules are known to exist, including DR, DQ and DP, each subset organized in alpha and beta heterodimers. These molecules play a central role in immunorecognition via direct noncovalent binding of degraded nonself immunogenic peptides followed by ligand-interaction with T cells. In the cytoplasm the class-II alpha and beta chains associate, in addition with a third backbone molecule known as the invariant chain. In this study we show that all class-II subsets associate with the invariant chain probably from the same pool and that a subset of invariant chain is expressed as a cell surface subunit. This sub-unit, whose function is still unknown, was detected by flow-cytometry and by two-dimensional gel analysis followed by antibody-mediated immunoprecipitations.

Frequency of abnormal expression of HLA-A,B,C and HLA-DR molecules, invariant chain, and LFA-3 (CD58) in colorectal carcinoma and its impact on tumor recurrence

HLA-A,B,C and HLA-DR molecules are involved in cognate LFA-3 (CD58) in antigen-independent T-cell/target-cell interaction. T-cell-mediated host-versus-tumor response might therefore depend on the presence of both types of molecules on the surface of the target cell. To investigate whether presence or absence of these molecules in colorectal carcinoma influences the recurrence rate, 149 patients who underwent curative surgery were surveyed for a maximum of 65 months (mean, 48 months). As determined by immunohistochemistry, aberrant reduction of HLA-A,B,C determinants was observed in 34.9 and a complete loss in 8.7% of the tumor specimens. An induction of HLA-DR molecules was found in 55.0 and of the HLA-DR-associated invariant chain (Ii) in 81.9%. An abnormal reduction of LFA-3 was detected in 43.6%, while a complete loss of this structure was observed in 6.7%. Reduction/loss of HLA-A,B,C was correlated with reduction/loss of LFA-3 (p = 0.03). In contrast to the prognostic role of tumor stage and grade, the presence vs. absence of all these structures was not correlated with the recurrence rate. We conclude that, although encoded on different chromosomes, an abnormal reduction/loss of HLA-A,B,C and LFA-3 might be the consequence of one transacting down-regulating signal. However, the resulting deviant immunophenotypes do not profoundly influence survival and growth potential of residual tumor cells.

Expression of HLA-A,B,C, beta 2-microglobulin (beta 2m), HLA-DR, -DP, -DQ and of HLA-D-associated invariant chain (Ii) in soft-tissue tumors

Non-neoplastic mesenchymal cells, along with 33 benign and 87 malignant soft-tissue tumors (STT) were examined for expression of HLA-A,B,C, beta 2-microglobulin (beta 2m), HLA-DR, -DP, and -DQ molecules and the HLA-D associated invariant chain (Ii). Serial frozen sections were immunostained using monoclonal antibodies (MAbs) to monomorphic framework determinants of HLA sublocus products, beta 2m and Ii, and to CD53, a recently defined broadly distributed pan-leucocyte molecule. Compared with the normal state, an induction/neo-expression of HLA-A,B,C/beta 2m was found in a considerable number of tumors of muscle, peripheral nerve, cartilage-forming, adipose, and vascular tissues. Conversely, some tumors of fibrous origin and of autonomic ganglia showed an abnormal abrogation/loss of HLA-A,B,C/beta 2m with respect to their cells of origin. Small, round tumor cells present in various types of STT exhibited a heterogenous pattern of expression of these molecules with a preponderance of HLA-A, B,C/beta 2m-negativity. HLA-D/Ii determinants were rarely detectable in STT. Besides their expression in some fibrohistiocytic tumors, they were only occasionally found in tumors of smooth-muscle, peripheral-nerve and vascular origin as well as in one clear-cell sarcoma. In all tumors but one, there was no microtopographic association between HLA-D/Ii-positive tumor cells and inflammatory cells. CD53 allowed discrimination between dendritic interstitial cells (DIC) and neoplastic cells and additionally revealed that, in contrast to other solid tumors, STT are generally characterized by an extreme scarcity of lymphohistiocytic infiltrates. Our data indicate that, aside from very rare exceptions, aberrant induction or abrogation of MHC molecules in STT occurs in the absence of lymphohistiocytic stromal infiltrates, suggesting that these alterations might not be a consequence of local cytokine effects.

The function of the invariant chain in antigen presentation by MHC class II molecules

The existence of different pathways of antigen presentation by class I and class II molecules raises two fundamental questions. (1) Why are class II, but not class I molecules, transported to the endosomal compartment where the exogenous antigen is met? (2) What are the mechanisms that prevent class II molecules from being occupied and blocked by endogenous peptides before they reach endosomes? These and other questions were discussed at the recent 7th International HLA/H-2 Workshop. In round table discussions particular attention was paid to the class-II-associated invariant chain, because it was considered that this molecule was a likely candidate to explain some of the differences of class I and class II molecules in antigen presentation.

Invariant chain trimers are sequestered in the rough endoplasmic reticulum in the absence of association with HLA class II antigens

HLA class II antigens are heterodimeric cell surface glycoproteins that interact with antigenic peptides to form complexes recognizable by CD4-positive T cells. During their biosynthesis, class II antigens are retained in a post-Golgi compartment in association with the invariant chain, which dissociates before class II cell surface expression. To address whether the invariant chain mediates this post-Golgi retention, its transport and assembly were examined in cells that do not express HLA class II antigens. Pulse-chase analysis and endoglycosidase digestions showed that very little invariant chain proceeded as far as the trans-Golgi in class II-negative cell lines. Immunofluorescence studies suggested that in these cells the invariant chain is sequestered in the RER. Gel filtration and cross-linking data showed that RER-localized invariant chain is present as trimers or aggregated trimers. Multimerization is mediated by lumenal interactions; a proteolytic fragment of the invariant chain corresponding to the lumenal domain remained trimeric as determined by cross-linking analysis. Similar transport and structural characteristics were observed for a pool of excess invariant chain in class II-positive cells, suggesting that an excess of invariant chain in the ER may be important for class II antigen function. These results have important implications for the transport of cellular proteins in general and for the role of the invariant chain in class II antigen biosynthesis.

Transcriptional control of the invariant chain gene involves promoter and enhancer elements common to and distinct from major histocompatibility complex class II genes

The invariant chain (Ii) is a glycoprotein coexpressed with the major histocompatibility complex (MHC) class II antigens. Although Ii is encoded by a single gene unlinked to the MHC gene complex, Ii and MHC class II appear to have similar patterns of tissue specific expression and generally are coordinately regulated by cytokines. Here we present evidence that transcription of the murine Ii gene is controlled by multiple cis-acting elements. The 5' regulatory region of the Ii gene appears to be combined of conserved class II regulatory elements with promoter elements commonly found in other eucaryotic genes. A region containing characteristic class II promoter elements (H box, X box, and a modified Y box) serves as an upstream enhancer in the Ii gene and might contribute to the coexpression of MHC class II and Ii genes. A series of positive control elements, the kappa B element, Sp1-binding site, and CCAAT box, are present in the Ii promoter and apparently serve distinct regulatory functions. The kappa B site in the Ii gene is a cell type-specific element, contributing to expression in a B-cell line but not in a fibroblast cell line, and the Sp1 site is required by the H-X-Y' enhancer element to stimulate promoter activity. In addition, an Ii enhancer in the first intron that specifically stimulates its own promoter has been identified. Our results suggest that a sequence match between enhancers and certain promoter elements is critical.

Transcriptional control of the invariant chain gene involves promoter and enhancer elements common to and distinct from major histocompatibility complex class II genes

The invariant chain (Ii) is a glycoprotein coexpressed with the major histocompatibility complex (MHC) class II antigens. Although Ii is encoded by a single gene unlinked to the MHC gene complex, Ii and MHC class II appear to have similar patterns of tissue specific expression and generally are coordinately regulated by cytokines. Here we present evidence that transcription of the murine Ii gene is controlled by multiple cis-acting elements. The 5' regulatory region of the Ii gene appears to be combined of conserved class II regulatory elements with promoter elements commonly found in other eucaryotic genes. A region containing characteristic class II promoter elements (H box, X box, and a modified Y box) serves as an upstream enhancer in the Ii gene and might contribute to the coexpression of MHC class II and Ii genes. A series of positive control elements, the kappa B element, Sp1-binding site, and CCAAT box, are present in the Ii promoter and apparently serve distinct regulatory functions. The kappa B site in the Ii gene is a cell type-specific element, contributing to expression in a B-cell line but not in a fibroblast cell line, and the Sp1 site is required by the H-X-Y' enhancer element to stimulate promoter activity. In addition, an Ii enhancer in the first intron that specifically stimulates its own promoter has been identified. Our results suggest that a sequence match between enhancers and certain promoter elements is critical.

Correlation of HLA-D/Ii antigen expression in breast carcinoma with local lymphohistiocytic infiltration reveals considerable dysregulation in a subset of tumors

Non-neoplastic mammary glands and 203 carcinomas of the breast were examined immunohistochemically for expression of HLA-DR, -DP, and -DQ molecules and the HLA-D-associated invariant chain (Ii). According to the reaction of normal breast epithelium in the course of chronic inflammation, these antigens were found to be induced in 120 carcinomas. In 106 of these the order was Ii greater than or equal to HLA-DR greater than or equal to HLA-DP greater than or equal to HLA-DQ. The extent of induction of these sequentially expressed antigens correlated with the density of local lymphohistiocytic infiltration (Ii: p = 0.003; HLA-DR: p = 0.0005; HLA-DP: p = 0.0000005; HLA-DQ: p = 0.01). Therefore, Ii/HLA-D antigen expression of carcinoma cells in local association with inflammation was regarded as an adequate reaction. The presence of these antigens in the absence of inflammation was regarded as "inadequate hyper-expression", and was found in 14 cases involving Ii, in 8 involving HLA-DR, and in 1 case each involving -DP and -DQ molecules. In contrast, 20 cases expressed minimal/no Ii despite heavy inflammatory infiltration. This "inadequate hypo-expression" was also found in 25 cases involving HLA-DR, in 30 involving -DP and in 40 involving -DQ determinants. Combining the 2 variants showed that at least 54 cases (26.6%) were characterized as being dysregulated. "Adequate vs. inadequate Ii/HLA-D antigen expression" did not correlate with tumor grading and might therefore be an independent parameter.

Cooperative effect of interferon-gamma and tumor necrosis factor-alpha on the induction of the class II antigen-associated invariant chain expression

The regulation of the invariant chain (Ii) expression was studied in the human colon carcinoma cell line HT-29 that constitutively expressed neither Ii nor class II antigens. Upon stimulation of HT-29 cells with a combination of human recombinant tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma), expression of mRNA and protein of the invariant chain were induced. In contrast, administration of TNF-alpha or IFN-gamma alone had no effect. A delayed induction of Ii mRNA, which was first detected 10-12 h after stimulation, was observed; this suggests an indirect regulatory mechanism. Stimulation with both IFN-gamma and TNF-alpha led to the co-expression of class II antigens with the invariant chain. In order to study the genetic basis for this stimulation the murine invariant chain gene (800 bp 5' flanking sequences and the structural gene) was transfected into HT-29 cells and transfected cells were tested for the ability to respond to IFN-gamma and TNF-alpha. Simultaneous application of both cytokines had a strong effect on the induction of the murine invariant chain. IFN-gamma alone had no effect and TNF-alpha only marginally stimulates murine invariant chain expression. The transfection experiment indicates that the murine invariant chain gene construct contains the structural elements which are responsible for regulation with IFN-gamma and TNF-alpha. We determined whether the cooperative effect of TNF-alpha and IFN-gamma is also found in vivo. Stimulations of mice were performed with TNF-alpha, IFN-gamma and a combination of both. The immunohistological analysis of kidney tissue sections revealed that TNF-alpha had no effect on Ii and Ia expression. Upon IFN-gamma treatment a minor subset of renal tubules showed staining for Ii, and less prominently also for Ia. However, simultaneous application of both cytokines led a strong induction of both Ii and Ia antigens in renal epithelial cells, thus suggesting that this synergistic effect potentially occurs under physiological conditions.

Recombinant gamma interferon and in vivo induction of HLA-DR antigens

Recombinant human IFN-gamma, used for treatment of melanoma and renal carcinoma, was found to induce HLA-DR expression on human keratinocytes in vivo. HLA-DR antigens bound to keratinocytes of the basal and suprabasal layers of the epidermis were observed after intramuscular or intravenous injections of 0.5 mg/kg body weight IFN-gamma, 3 times a week. Keratinocyte-bound HLA-DR antigens were first observed at the beginning of the third or fourth week of treatment, but HLA-DQ and HLA-DP antigens were never detected on keratinocytes. The intracytoplasmic constant (gamma) chain of the class II molecules was also not detectable within the keratinocytes. Patients who received IFN-alpha 2 therapy, did not exhibit keratinocyte-bound HLA-DR antigens.

Genetic mapping of the mouse c-fms proto-oncogene to chromosome 18

Chinese hamster X mouse somatic cell hybrids were analyzed by Southern blot hybridization with a probe specific for the cellular c-fms proto-oncogene. Results demonstrate that Fms, the genetic locus containing this sequence, maps to mouse chromosome 18. Mouse Fms is thus not linked to the same set of genes involved in growth regulation that human FMS is linked to.

Differential expression of HLA-DR, HLA-DP, HLA-DQ and associated invariant chain (Ii) in normal colorectal mucosa, adenoma and carcinoma

The expression of MHC class II antigens (HLA-DR, HLA-DP and HLA-DQ) and the associated invariant chain (Ii) was studied in epithelial cells of normal colorectal mucosae, colorectal adenomas and carcinomas, using a sensitive immunoperoxidase technique with monoclonal antibodies on frozen sections. In contrast to class II antigens, Ii was detected in some normal mucosae distant from the tumour. In residual non-neoplastic mucosa adjacent to carcinomas, Ii and class II antigens were induced in the order Ii greater than or equal to HLA-DR greater than or equal to HLA-DP greater than or equal to HLA-DQ, the reactions being most pronounced in cases with inflammatory alteration of the crypts. In 22/37 adenomas and 77/123 carcinomas, Ii expression clearly exceeded class II antigen expression. Class II antigens were found in 20/37 adenomas and 62/123 carcinomas, mostly in a non-coordinate manner, following the above order. A detailed analysis of the expression patterns in normal and neoplastic colon epithelial cells revealed a closer association of HLA-DP with HLA-DQ than of HLA-DR with HLA-DP, or HLA-DQ.

Chromosome maps of man and mouse, III

Data on loci whose positions are known in both man and mouse are presented in the form of chromosomal displays, a table, and autosomal and X-chromosomal grids. At least 40 conserved autosomal segments with two or more loci, as well as 17 homologous X-linked loci, are now known in the two species, in which mitochondrial DNA is also highly conserved. Apart from the Y, the only chromosome now lacking a conserved group is human 13. Human 17 has a single conserved group which includes both short and long arms, and so may have remained largely intact in mammalian evolution. Human and mouse chromosomal maps show the approximate locations of homologous genes while the mouse map also shows the positions of translocations used in gene location.

Four Ia invariant chain forms derive from a single gene by alternate splicing and alternate initiation of transcription/translation

We determined the structural basis for the presence of electrophoretically-distinct, antigenically-related forms of invariant chains in Ia oligomers, and established the mechanisms by which they can be expressed from a single gene. S1 nuclease protection assays indicated that, in B cells, transcription of this gene initiates at a minimum of three sites. Thus, unlike previously thought, invariant chain mRNAs have heterogeneous 5' untranslated segments that may differentially affect initiation of translation. Further, restriction mapping and nucleotide sequencing of cDNAs revealed two kinds of invariant chain mRNAs differing by an internal coding segment of 192 bp. This segment represents an alternatively spliced exon, as demonstrated by nucleotide sequencing of corresponding genomic regions. The exon (exon X) encodes a cysteine-rich stretch of 64 amino acids near the COOH terminus that displays a striking and surprising homology to an internal amino acid repeat of thyroglobulin, suggesting an evolutionary mechanism of exon shuffling. Transient expression of cDNAs indicated that both types of alternatively spliced mRNAs contain two in-frame AUGs functioning as alternate start sites for translation. Thus, transfections with exon X-lacking cDNAs resulted in the expression of Mr 33,000 and 31,000 proteins, detected by immunoprecipitation with anti-invariant chain antisera, and identical by two-dimensional gel (2-D) analyses to the B cell invariant-chain forms gamma 1 (Mr 31,000), gamma 2, and gamma 3 (Mr 33,000). Similarly, exon X-containing cDNAs expressed Mr 43,000 and 41,000 proteins, also identical by 2-D migration to Ia-associated proteins. Thus, human Ia molecules contain four forms of invariant chain of closely related but nonidentical primary structure that are generated from a single gene by a complex pattern of alternate transcriptional start, exon splicing, and translational start.

Cell surface expression of class II histocompatibility antigens occurs in the absence of the invariant chain

The invariant chain is a glycoprotein transiently associated with the alpha and beta subunits of class II antigens of the major histocompatibility complex during their transport to the cell surface. An expression assay with cDNA clones transfected into simian COS cells was used to test whether the invariant chain is required for assembly and transport of human class II antigens. COS cells do not express detectable levels of RNA from the endogenous invariant chain gene. Cell surface expression of the DP, DQ, and DR antigens was observed in COS cells transfected with the respective alpha and beta chain cDNA clones. Analysis of RNA from the transfected cells showed that the human genes were transcribed in COS cells and that the endogenous simian class II and invariant chain genes were not induced. Cotransfections with an invariant chain cDNA clone did not alter the levels of class II antigens at the cell surface. Biosynthetic labeling and immunoprecipitation demonstrated that the invariant chain cDNA was expressed into a protein which associated with DR alpha and beta chains. Efficient expression of DR antigen in absence of invariant chain was also observed at the surface of a human fibroblast line stably transfected with DR alpha and beta cDNA. This study demonstrates that expression of all three human class II antigens can be achieved with cDNAs cloned in expression vectors. Furthermore, cell surface expression of class II major histocompatibility complex antigens can occur in absence of invariant chain. The postulated role of the invariant chain in class II antigen transport to the cell surface must be reevaluated. The invariant chain may rather be involved in functional properties of class II molecules such as antigen presentation.

Structure of the human Ia-associated invariant (gamma)-chain gene: identification of 5' sequences shared with major histocompatibility complex class II genes

The human gene encoding the Ia-associated gamma (or invariant) chain was isolated by screening a genomic library in phage lambda with cDNA probes. The frequency of positive clones in the library, the overlapping restriction maps of the cloned fragments, and the patterns of genomic hybridization suggested that the gamma-chain gene exists as a single copy per haploid genome. The gene consists of 8 exons, spanning approximately 12 kilobases of DNA. All exon sequences were in an open reading frame, contained appropriate splice junction sequences, and encompassed the entire sequence of full-length gamma-chain mRNA, suggesting that the gene we isolated is most likely functional. Furthermore, "CAAT"-type and "TATA"-type promoter sequences were found at the expected positions upstream from the proposed cap site. The organization of the gamma-chain gene has none of the distinctive features of the immunoglobulin superfamily of genes, of which Ia alpha and beta chains are members. Therefore, the evolutionary origins, and perhaps the functions, of the Ia gamma chains are distinct from those of the other two Ia subunits alpha and beta. Despite the unrelatedness of these genes, consensus sequences found approximately 150 base pairs upstream from all the Ia alpha- and beta-chain genes sequenced to date were also found in analogous positions in the gamma-chain gene, suggesting a possible role in the coregulation of expression of these genes.

Molecular analysis of HLA class I and class II antigen loss mutants reveals a homozygous deletion of the DR, DQ, and part of the DP region: implications for class II gene order

The mutant human B-lymphoblastoid cell lines, 721.174 and 721.180, previously reported to exhibit greatly reduced expression of human HLA class I and II antigens (DeMars et al., Hum Immunol 11:77, 1984), were analyzed by Southern blotting using class II cDNA and genomic clones as hybridization probes. All genomic sequences complementary to DR alpha, DR beta, DQ alpha, and DQ beta probes were absent from these mutants. DZ alpha genomic sequences were deleted as were the DP alpha 1 and DP beta 1 loci but the DP beta 2 and most, if not all, of the DP alpha 2 locus were retained. However, no RNA transcripts for either DP alpha 2 or DP beta 2 could be detected. The mapping of the deletion breakpoint within the DP cluster allows the orientation of the loci in the DP region with respect to the centromere as follows: centromere, DP beta 2, DP beta 1, DP alpha 1, (DQ, DR). In addition, the analysis of a set of DR-, DQ-, DP+ homozygous deletion mutants (721.82, 721.84, and 721.101) reveals a deletion breakpoint between the DQ alpha 1/DQ beta 1 loci and the DQ alpha 2/DQ beta 2 loci. These mutants retain DZ alpha genomic sequences, tentatively mapping the DZ alpha locus between the DQ and the DP region. The residual ability of the DR-, DQ-, DP- mutants (174 and 180)* to stimulate allogeneic and autologous lymphoproliferative responses must be attributed to expression of as yet unidentified class II antigens, or to non-class II antigens.

Determination of attachment sites for N-linked carbohydrate groups of class II histocompatibility alpha-chain and analysis of possible O-linked glycosylation of alpha- and gamma-chains

Two glycopeptide fractions were isolated from a tryptic digest of the human class II antigen alpha-subunit, by chromatography on Lens culinaris and Ricinus communis lectin columns, respectively. Partial NH2-terminal sequence analysis of radiochemically labelled glycopeptide fractions allowed alignment with two stretches of the deduced DR alpha sequence, each encompassing a signal for N-linked glycosylation, i.e. Asn-X-Thr(Ser). The fraction displaying affinity for L. culinaris lectin was susceptible to the action of endo-beta-N-acetylglucosaminidase H whereas the fraction adsorbed to R. communis was not. Since DR alpha is known to carry only one N-linked carbohydrate chain in the high-mannose form, this glycan could thereby be mapped to Asn 78. Accordingly, the complex N-linked carbohydrate is attached to Asn 118. Moreover, analysis of material released from class II antigens and gamma-chains upon mild alkaline hydrolysis, indicates the presence of O-linked sugars on the alpha- and gamma- but not the beta-subunits.

Structure of the human gene encoding the invariant gamma-chain of class II histocompatibility antigens

The primary structures of a cDNA and the genomic DNA of a gene selectively expressed in chronic lymphocytic leukemia were determined. A computer search of the nucleotide sequence data bank identified this gene as the invariant gamma-chain associated with class II histocompatibility antigens. The invariant gamma-chain genomic sequence spans about 11 kilobases, with eight exons and seven introns. Three of the introns contain members of the Alu repeat family. A putative cap site and promoter sequence were identified at the 5' end of the gene. One or two copies of the gene is present in each haploid genome, and no evidence for amplification or polymorphism was obtained.

Assignment of the human gene for the glucocorticoid receptor to chromosome 5

Human lymphoblastic leukemia cells of line CEM-C7 are glucocroticoid-sensitive and contain glucocorticoid receptors of wild-type characteristics. EL4 mouse lymphoma cells are resistant to lysis by glucocorticoids due to mutant receptors that exhibit abnormal DNA binding. Hybrids between the two cell lines were prepared and analyzed with respect to glucocorticoid responsiveness and to receptor types by DNA-cellulose chromatrography. Sensitive hybrid cell clones contained the CEM-C7-specific receptor in addition to the EL4 type of receptor. Several sensitive hybrid cell clones were used for selection of resistant segregants by growth in the presence of high concentrations of glucocorticoid. These segregants had lost the wild-type CEM-C7 receptor, while the EL4-specific receptor was retained. To identify the human chromosome that was lost concordantly with the CEM-C7 receptor the chromosomes of hybrid cells were studied by alkaline Giemsa (G-11) staining and trypsin/Giemsa banding. All hybrids contained human chromosomes in addition to one to two sets of EL4 chromosomes. Human chromosome 5 was present in all hybrid cell clones that expressed the CEM-C7 receptor and it was absent from those that did not. This absolute correlation was not observed for any other human chromosome. We conclude that the human gene for the glucocorticoid receptor is located on chromosome 5.

The gene encoding the Ia-associated invariant chain is located on chromosome 18 in the mouse

The chromosomal assignment of the gene encoding the invariant (Ii) chain associated with the mouse immune response antigens (Ia) was determined by Southern blot analysis of DNA from a panel of mouse X Chinese hamster somatic cell hybrids cleaved with Hind III or Eco RI. Using a mouse li cDNA as a hybridization probe, we localized the gene coding for the invariant chain to mouse chromosome 18.