A novel family of human major histocompatibility complex-related genes not mapping to chromosome 6

Chromosome maps of man and mouse. IV

Current knowledge of man-mouse genetic homology is presented in the form of chromosomal displays, tables and a grid, which show locations of the 322 loci now assigned to chromosomes in both species, as well as 12 DNA segments not yet associated with gene loci. At least 50 conserved autosomal segments with two or more loci have been identified, twelve of which are over 20 cM long in the mouse, as well as five conserved segments on the X chromosome. All human and mouse chromosomes now have conserved regions; human 17 still shows the least evidence of rearrangement, with a single long conserved segment which apparently spans the centromere. The loci include 102 which are known to be associated with human hereditary disease; these are listed separately. Human parental effects which may well be the result of genomic imprinting are reviewed and the location of the factors concerned displayed in relation to mouse chromosomal regions which have been implicated in imprinting phenomena.

Molecular cloning of CD1a (T6), a human epidermal dendritic cell marker related to class I MHC molecules

To investigate the structure, function, and control of CD1a, we have cloned a 1.6-kbp cDNA which encodes the expressed CD1a protein and includes untranslated 5' and 3' sequences and the poly-A tail. As the protein recognized by the monoclonal antibody OKT6, CD1a is a useful marker for Langerhans cells (LC). CD1a is found on these cells and on thymocytes, suggesting an important immunologic role for this molecule. We constructed a cDNA library in lambda gt10 using mRNA from MOLT-4, a cell line that expresses the CD1a surface antigen. We then screened the library with an oligonucleotide synthesized according to a known partial sequence for CD1a, and subcloned the cDNA and its restriction fragments into pGEM for sequencing and probe production. Based on this sequence the CD1a protein is predicted to consist of three extracellular domains (alpha 1-3), a hydrophobic transmembrane region, and a cytoplasmic tail. DNA 5' to the alpha 1 region may undergo alternative exon splicing. There is high sequence identity between the beta-2 microglobulin binding region of MHC I molecules and CD1a. The secondary structure predicted for CD1a is very similar to the actual structure of HLA-A2, a classical MHC I molecule. The similarity includes the beta pleated sheets and alpha helices which form the antigen binding groove of the alpha-1 and alpha-2 domains. The homology predicted between CD1a and HLA-A2 in these regions appears to exist on the level of secondary structure despite low primary nucleotide and amino acid sequence identity. The structural data and probes we have developed should facilitate studies of the function of CD1a as well as novel investigations of LC.

Phorbol esters potentiate the induction of class I HLA expression by interferon alpha

We have studied the effect of phorbol esters on the induction of class I histocompatibility antigen (HLA) expression by interferons (IFNs) in the T-cell line MOLT-4 and in the MOLT-4 mutant YHHH. Addition of IFN-alpha to phorbol 12,13-dibutyrate-pretreated MOLT-4 cells causes a greater than 20-fold increase in the expression of class I HLA, as compared to a 4- to 7-fold IFN-alpha-induced increase in control cells. Pretreatment with phorbol 12,13-dibutyrate does not alter the class I HLA response to IFN-gamma or the responses of other IFN-induced genes. This effect of phorbol 12,13-dibutyrate reproduces in MOLT-4 cells the phenotype of the mutant YHHH, which also displays a selective enhanced class I HLA response to IFN-alpha. Pretreatment of YHHH with phorbol 12,13-dibutyrate does not affect any of the responses induced by IFN. These findings suggest the existence of a phorbol ester-sensitive factor, inducible in MOLT-4 and constitutively expressed or modified in YHHH, which operates in the pathway of induction of class I HLA by IFN-alpha but not in the pathway used by IFN-gamma.

Two classes of CD1 genes

Herein, we report the DNA sequence of two human CD1 genes, R2 and R3, distinct from those encoding the CD1a, -b and -c antigens. Both genes appear to have an exon/intron structure analogous to the previously analyzed CD1 genes and to be functional on the basis of their sequence. Analysis of the variability patterns, potential intramolecular interactions and predicted secondary structure profile on an alignment of all known CD1 alpha chains suggest some shared structural features with major histocompatibility complex class I molecules in the alpha 1 domains but substantial differences in the alpha 2 domains. Sequence comparison shows that, while R2 is most related to CD1a, -b and -c, albeit to a somewhat lower degree than the latter are to themselves, R3 is more homologous to mouse than to human CD1, suggesting the existence of two functional classes within the CD1 gene family. We propose to retain the non-committal R2 and R3 names until the putative antigens have been identified and their tissue distribution has been established.

An Fc receptor structurally related to MHC class I antigens

Maternal immunoglobulin G transmitted to the fetus or newborn provides humoral immunity for the first weeks of mammalian life. Fc receptors on intestinal epithelial cells of the neonatal rat (FcRn) mediate the uptake of IgG from milk. Affinity-purified FcRn is resolved by SDS-PAGE into components of relative molecular masses 45,000-53,000 (p51) and about 14,000 (p14). We report the identification of the smaller component as beta 2-microglobulin. Association of beta 2-microglobulin with p51 was confirmed by crosslinking in intestinal epithelial cell brush borders. We have cloned a cDNA encoding the presumptive Fc-binding subunit, p51, and its predicted primary structure has three extracellular domains and a transmembrane region which are all homologous to the corresponding domains of class I major histocompatibility complex (MHC) antigens. This is the first time a function has been assigned to an MHC antigen-related molecule.

Isolation and characterization of a cDNA and gene coding for a fourth CD1 molecule

The CD1 locus encodes a family of major histocompatibility complex (MHC) antigen-like glycoproteins which associate with beta 2-microglobulin and are expressed on immature thymocytes and Langerhans cells. Three CD1 molecules have been identified by monoclonal antibodies and molecular cloning: CD1a, -b, and -c. We have isolated a cDNA coding for a fourth CD1 molecule from a human thymocyte library and termed this molecule CD1d. Reported here are the complete nucleotide sequence and genomic organization of CD1d. They predict that this molecule is related to the previously identified CD1a, -b, and -c molecules and to MHC class I molecules, with three external domains, a transmembrane domain, and a short cytoplasmic tail. The sequence of CD1d is the most divergent among the CD1 molecules in the membrane-distal alpha 1 and alpha 2 domains and in the 5' untranslated region. In contrast, all four CD1 molecules are highly homologous in the membrane-proximal alpha 3 domain, which is likely involved in beta 2-microglobulin binding. A comparison of CD1 and MHC class I sequences suggests that these molecules each evolved to interact with a distinct set of cell surface proteins.

A second chain of human CD8 is expressed on peripheral blood lymphocytes

Human CD8 has been thought to consist of disulfide-linked homodimers and homomultimers of a single polypeptide chain homologous to mouse and rat CD8 alpha. In contrast, mouse and rat CD8 are composed of disulfide-linked heterodimers of alpha and beta chains. We have now isolated and sequenced cDNA clones encoding a human homologue of mouse and rat CD8 beta. One such clone was inserted into an expression vector and its encoded product was shown to be expressed on the cell surface after cotransfection into L cells with the human CD8 alpha gene. A second form of human CD8 beta cDNA encoding a protein with an altered cytoplasmic tail was similarly transfected, but its product could not be demonstrated on the cell surface. CD8 beta was further shown to be expressed on the surface of almost all CD8+ human peripheral blood T cells. These data provide the first evidence that human CD8 is a heterodimeric protein.

Mouse CD1 is distinct from and co-exists with TL in the same thymus

Human CD1 antigens have a similar tissue distribution and overall structure to (mouse) TL. However recent data from human CD1 suggest that the mouse homologue is not TL. Since no human TL has been conclusively demonstrated, we have analysed the murine CD1 genes. Two closely linked genes are found in a tail to tail orientation and the limited polymorphism found shows that, as in humans, the CD1 genes are not linked to the MHC. Both genes are found to be equally transcribed in the thymus, but differentially in other cell types. The expression in liver, especially, does not parallel CD1 in humans. This demonstrates conclusively that CD1 and TL are distinct and can co-exist in the same thymus. It is paradoxical that despite the structural similarity between mouse and human CD1, the tissue distribution of human CD1 is closer to TL. The possibility of a functional convergence between MHC molecules and CD1 is discussed.

CD1c antigens are present in normal and neoplastic B-cells

The immunohistochemical detection of CD1c antigen is described in mantle zone B-cells of the tonsil, lymph node, and spleen, and also in the marginal zone B-cells of the spleen. CD1c expression was observed in most cases of low-grade, but in only a single case of high-grade, B-cell non-Hodgkin's lymphoma. It was not detected in germinal centre cells, nor in Epstein-Barr virus-transformed or Burkitt's lymphoma B-cell lines. This distribution suggests that CD1c expression may occur preferentially in slowly proliferating B-cell populations and does not support previous suggestions that CD1c is a human equivalent of the mouse thymus leukaemia antigens.

Biochemical properties of a novel rabbit thymocyte specific class I-like antigen

Monoclonal antibody 5E2 identifies a new rabbit thymocyte specific cell surface molecule designated R-Ta. SDS-PAGE of molecules immunoprecipitated by 5E2 shows that R-Ta exists as a non-covalently associated hetero-dimer consisting of a light polypeptide chain (mol. wt approximately 12,000) and a bi-molecular species of a heavy chain (mol. wts of 45,000 and 40,000). The difference between the two forms of heavy chain can be attributed to different degrees of glycosylation. Each form of the R-Ta heavy chain has a polypeptide mol. wt of 34,000. At least three N-linked oligosaccharides and no significant O-linked sugars were found associated with R-Ta. Two dimensional electrophoresis of V8 protease peptide maps also indicate that the two forms of the heavy chains are similar, if not identical, in polypeptide primary structure. The light polypeptide was found to be serologically and structurally identical to beta-2-microglobulin. This was demonstrated in a previous study by reaction with goat anti-beta-2-microglobulin antisera. In this investigation the structural identity with beta-2-microglobulin was demonstrated by partial amino terminal sequence analysis. The partial amino acid sequence for 18 steps of the R-Ta heavy chain was also determined. A comparison of the amino acid sequence with other known sequences for the conventional Class I molecules of man, mouse and rabbit did not reveal any homology. Thus R-Ta is a new T-cell surface protein, and like human CD1, carries the unique distinction of thymocyte specificity, is beta-2-microglobulin associated, but is not Class I related.

MHC class I expression by developmental tumors: teratocarcinoma stem cells are TCA positive

We have investigated the expression of antigens recognized by several alloantisera and monoclonal antibodies to class I and class I-like MHC gene products on four developmental tumor cell lines derived from teratocarcinoma and choriocarcinoma. The analysis by cytotoxicity, immunoprecipitation, and Northern blotting analysis was also performed following treatment of the cells with gamma interferon. Three of four of the cell lines apparently do not express polymorphic determinants of HLA-A,B,C class I MHC genes. Immunoprecipitation with antibodies to HLA monomorphic determinants or beta 2m showed that some cell lines express distinct novel class I MHC-like molecules; the latter show molecular sizes different from regular HLA molecules and are associated with beta 2m. The Northern blotting showed class I mRNA present in three out of four of the developmental tumor cell lines but at at least tenfold lower levels than in lymphoid cells; it is possible that the RNAs homologous to class I DNA probes include transcripts of non-HLA-A,B,C genes. The cells were serologically typed for one such locus, TCA, which lies telomeric to HLA-A; the choriocarcinomas are negative and the teratocarcinomas are positive. The relationship between the different antigenic molecules and their possible functional significance is discussed in terms of maternofetal interactions, cancer, and transplantation.

HLA class I molecules are associated with CD1a heavy chains on normal human thymus cells

The molecules encoded by the major histocompatibility complex play a pivotal role in regulatory interactions between cells of the immune system, which can result in the activation and function of T cells. The function of the CD1 molecules, which are homologous to the major histocompatibility complex-encoded molecules but are encoded on human chromosome 1, is not known. HLA class I molecules and CD1a heavy chains share the ability to associate with several different cell-surface molecules. We show here, by several technical approaches, that HLA class I molecules are associated with CD1a heavy chains on the surface of normal thymus cells. The functional significance of this association during T-cell differentiation is discussed.

Characterization of a bovine thymic differentiation antigen analogous to CD1 in the human

Three monoclonal antibodies (MoAb), TH97A, CC13, and CC14, define a thymic differentiation antigen in cattle. The antigen is expressed on 50-60% of bovine thymocytes, located mainly in the cortical areas, but is not expressed on peripheral blood mononuclear cells (PBMC). In cryostat sections of lymph node, the antibodies react with large dendritic-like cells in the paracortical regions. They also react with a proportion of the large 'frilly' cells in afferent lymph and with dendritic-like cells in the dermis. The antibodies apparently do not react with cells in the epidermis. Biochemical analysis of the antigen recognized by MoAb TH97A reveals two bands of 44 kDa and 12 kDa under reducing conditions. These polypeptides are distinct from bovine class I major histocompatibility complex molecules reactive with the MoAb w6/32. The tissue distribution of positive cells together with results of biochemical analyses indicate that the antigen recognized by these MoAb is the bovine analogue of the human CD1.

Lymphoma-specific T- and B-cell responses suggest the involvement of HTLV-I in virus-non-productive lymphomas of a married couple

In a married couple, a T-cell and a B-cell lymphoma occurred at the same time in the husband (FR) and wife (FE), respectively. Serum antibodies of patient FE with less advanced tumor progression specifically recognized HTLV-I-related envelope precursor molecules of 66-68 kDa molecular mass on HTLV-I-infected T- and B-cell lines, but not on HTLV-II or HIV-infected cells. In addition, in vivo-activated CD8+ T-cell lines (TCL) from this patient specifically lysed autologous B-lymphoma cells, T-lymphoma cells from the husband (FR), as well as the HTLV-I-transformed MT2 T-cell line. All positive target cells shared an HLA-class-I cross-reactive determinant identified by the alloantiserum WER127. On a clonal level, the specificity of the cytotoxic T-cell response was unequivocally distinguishable from classical natural-killer-like cytotoxicity. Results imply the involvement of a common inductive agent in the manifestation of malignant lymphoma in both patients (FR and FE). Since antibodies from cases with classical HTLV-I-induced adult T-cell leukemias (ATLL) did not bind antigens on cells of either lymphoma (FR or FE) and active virus production was not demonstrable under various different conditions, these results argue against HTLV-1 itself being the transforming agent. However, humoral and cellular immune responses of one patient (FE), in addition to de novo HLA-class-1 antigen expression of both patients, are nonetheless consistent with the involvement of viral infections(s). These were responsble for the expression of HTLV-1-characteristic envelope determinants of the malignant progeny of respective T- and B-cell origin.

Characterization of a T-lymphocyte Epstein-Barr virus/C3d receptor (CD21)

The Epstein-Barr virus/C3d receptor (EBVR-CR2) was detected on three T-lymphoblastoid cell lines. The apparent Mrs of purified EBVR-CR2 of T-cell and B-cell origin were identical. The N-terminal amino acid sequence from the T-cell EBVR-CR2 confirmed the placement of this receptor in a multigene family of complement regulatory proteins. All EBVR-CR2-positive T-cell lines were T6 and T4-T8 antigen positive.

Intermolecular complexes between three human CD1 molecules on normal thymus cells

The first cluster of differentiation (CD1) defines at least three distinct human thymic cell-surface differentiation antigens-CD1a, CD1b, and CD1c. We looked for structural homology of the three CD1 heavy chains at their peptide level by two-dimensional peptide maps. We show here that the CD1a Mr 49,000 heavy chain and the CD1b Mr 45,000 heavy chain appear to be more homologous to each other than to the CD1c Mr 43,000 heavy chain and that only one tyrosil peptide is common to the three heavy chains. Study of the CD1 heavy chains from several individuals reveals a very limited polymorphism of these molecules. We also demonstrate here that CD1a or CD1a-like molecules and other CD1 molecules can form intermolecular complexes on the surface of normal thymus cells. Molecules that are structurally very similar to CD1a molecules are associated noncovalently either with CD1c molecules or with CD1b molecules, and only CD1a molecules can associate covalently with CD8 molecules. In contrast, we could not find these intermolecular complexes on the surface of leukemic T-cell lines in culture.

Human cytomegalovirus encodes a glycoprotein homologous to MHC class-I antigens

Primary infection with human cytomegalovirus (HCMV) is persistent and widespread, with symptoms that are mostly subclinical but can cause serious illness or death, particularly in immunosuppressed patients. Recently, proteins from HCMV were shown to bind beta 2-microglobulin (beta 2-m) a protein that is normally found associated with the class-I major histocompatibility complex (MHC) antigens, which are essential for self-non-self recognition in the immune response. These findings led to the proposal that the virus may use beta 2-m binding as an infection mechanism. Here we present evidence from DNA sequence analysis that HCMV encodes a molecule similar to the MHC class-I antigens of higher eucaryotes, and propose that this protein is responsible for the observed beta 2-m binding. The deduced amino-acid sequence of the HCMV class-I-like protein reveals conservation of typical features of class-I structure, but we predict that the gene is not spliced, in contrast to the cellular genes.

Correlated expression of surface antigens in human thymocytes. Evidence of class I HLA modulation in thymic maturation

The correlated expression of several surface antigens (CD 1, class I HLA, CD3) was examined in human unfractionated thymocytes or selected subsets by using single or double-color flow cytometry. Prethymocyte subpopulations expressed high levels of HLA. A high proportion of cortical cells expressed low levels of either HLA or CD 3 antigens. Most of these HLA+ cortical cells corresponded to the more immature cells and did not express HLA-B loci products. CD 1 a and CD 3 antigens were expressed in a high percentage of cells and the levels of expression of each antigen in individual cells were inversely correlated. These data and the contour of double-color histograms are suggestive of the existence of a single pathway of thymocyte differentiation in which class I HLA expression is switched off around the time of the initiation of CD 3 (and Ti?) expression. We suggest that the anti-major histocompatibility complex (MHC) specificity of the unselected Ti receptor may be incompatible with the expression of MHC products on the cell membrane. At this stage, CD 1 antigens, whose expression is inversely correlated with that of HLA, may fulfill the role of MHC antigens. The latter can be re-expressed later on, once the anti-MHC specificities of the Ti receptors have been selected against. Studies on in vitro modulation of HLA molecules by interferon-alpha did not reveal any correlation to the expression of CD 1 or CD 3 antigens.

Transfer and expression of three cloned human non-HLA-A,B,C class I major histocompatibility complex genes in mutant lymphoblastoid cells

The HLA-A, -B, and -C class I human histocompatibility antigens and the genes that encode them have been isolated and characterized. Apparently complete class I non-HLA-A, B, C genes have been identified on HindIII-generated 5.4-kilobase (kb), 6.0-kb, and 6.2-kb DNA fragments derived from lymphoblastoid cell line (LCL) 721. We studied the expressibility of these genes by subcloning them into the nonintegrating pHeBo vector and transferring the chimeric plasmids into mutant LCL 721.221. This mutant was derived from LCL 721 by means of immunoselections following gamma-ray mutagenesis that eliminated expressions of the HLA-A, -B, and -C alpha chains. The HLA-A, B, C-null phenotype of mutant 721.221 made it possible to monitor the expression of class I genes transferred into it by assaying cell surface binding of monoclonal antibodies BBM.1 and W6/32, which recognize beta 2-microglobulin and HLA class I alpha-chain epitopes, respectively. Increased binding of BBM.1 and W6/32 was clearly observed in transferents containing the class I gene of the 6.0-kb DNA fragment but not in transferents containing the class I genes of the 5.4- and 6.2-kb DNA fragments. However, one-dimensional gel electrophoresis of BBM.1 and W6/32 immunoprecipitates made with [35S]methionine-labeled cell lysates showed that transfer of each non-HLA-A, B, C class I gene into 721.221 resulted in the appearance of an alpha chain that coprecipitated with beta 2-microglobulin. The three previously unreported alpha chains differed from each other in size and were smaller than HLA-A, -B, and -C alpha chains. These observations clearly show that these three cloned, nonallelic, non-HLA-A, B, C class I genes encode alpha chains that can be expressed in human cells.

Further studies on the heterogeneity of antigens recognised by CD-1 monoclonal antibodies: distribution of epitopes and analysis of serological binding patterns

The binding patterns of 28 monoclonal antibodies (MAB) recognizing antigens belonging to Cluster of Differentiation One (CD-1) were analyzed in order to investigate heterogeneity within this cluster. Competitive binding assays using radiolabelled MAB provided detailed information on CD-1 antigenic heterogeneity, and demonstrated that at lease six epitopic regions are recognised as CD-1 MAB. Further studies, based on single cell suspension immunofluorescence assays (using thymocytes and subclones on the cell line Molt-4), suggested that the majority of MAB studied could be serologically separated into three groups. In view of the most recent information that CD-1 MAB recognize at least three different early T-cell differentiation molecules, our results indicate that there are three or more distinct epitopes on the 'gp49'(HTA-1/CD-1a) molecule, two on the 'gp45'(HTA-3/CD-1b) molecule and one on 'gp43'(HTA-2/CD-1c).

Structure and expression of the human thymocyte antigens CD1a, CD1b, and CD1c

The CD1 human antigens are a family of at least three components, CD1a, CD1b, and CD1c, that are characteristic of the cortical stage of thymocyte maturation. CD1a was originally named HTA1 or T6 and thought to be the human equivalent of mouse Tla. The genes coding for all three have now been identified by transfection into mouse cells. The transfectants express the surface antigens that can then be recognized by the corresponding cluster of monoclonal antibodies used to define the three members of CD1. The full sequence of the genomic DNA is described for all three. The intron-exon structure of CD1a is deduced by comparison with a near-full-length cDNA clone. Similar structures are proposed for the other two, largely based on sequence homology. An unusually long 5'-untranslated exon (280 bases long) is highly conserved between the three genes, suggesting an important but unknown function. CD1c has a duplicated form of this exon that is thought to be spliced out. The major homology between the three antigens is in the beta 2-microglobulin-binding domain. The general relatedness to major histocompatibility complex class I and class II molecules is significant but low, with no section of higher homology to mouse Tla.

Human leukocyte antigens: an update on structure, function and nomenclature

The study of human leukocyte antigens, predominantly by monoclonal antibody techniques, is a rapidly changing area of basic research and clinical investigation. This review outlines some of the results and trends of research in this field. Of particular importance is the updating of the current nomenclature. The CD classification of these antigens has become the standard form in published literature and provides a basis for standardization of clinical reporting. The current CD classification is presented in the form of a list, with a brief summary of each antigen beside each entry. The results reviewed range from the section on CD1 antigen in which the data presented are primarily concerned with the underlying biology of the antigens to the section on clinical application which has little biological content.

Human epidermal Langerhans cells internalize by receptor-mediated endocytosis T6 (CD1 "NA1/34") surface antigen. Birbeck granules are involved in the intracellular traffic of the T6 antigen

Using immunogold staining of a suspension of living human epidermal cells to identify the Langerhans cell membrane-associated antigen T6 (revealed by the monoclonal antibody BL6), we have observed internalization of T6 antigen in Langerhans cells. This phenomenon is at least partly due to receptor-mediated endocytosis involving coated pits, coated vesicles, endosomes, the smooth endoplasmic reticulum, and lysosomes. These ultrastructural results suggest that T6 antigen may be part of a receptor site. Following receptor-mediated endocytosis, the appearance in the cell center of the first labeled Birbeck granules suggests that Birbeck granules could represent T6 intracellular transport organelles carrying T6 from the central part of the cell to an unknown destination.

Identification in rat liver and serum of water-soluble class I MHC molecules possibly homologous to the murine Q10 gene product

We have identified large quantities of a water-soluble, non-RT1.A class I MHC molecule in the serum of the DA rat strain, with a similar molecule being found in aqueous extracts of DA liver. The non-RT1.A class I molecules have heavy chains of 41 kD, which is smaller than RT1.A class I molecules isolated from liver membranes (45 kD) but larger than water-soluble RT1.A class I molecules previously identified in serum and aqueous extracts of liver and kidney (40 kD). NH3-terminal amino acid sequencing of bulk-purified RT1.A class I molecules and of this novel non-RT1.A class I molecule revealed two substitutions, in the first 25 amino acids, Tyr----His at position 9, and Ala----Ser at position 24. The non-RT1.A class I molecule did not react with any of the well-characterized polymorphic and monomorphic antibodies directed against RT1.Aa class I molecules, but did react with the MRC OX18 antibody. A similar class I molecule could not be identified on liver membranes. The non-RT1.A class I molecule was found in large quantities (approximately 20 micrograms/ml) in the serum of the DA rat strain, and similarly large quantities appeared to be present in the sera of BN, PVG, and LEW.RT1a rats. WAG and LEW.RT1u rats had readily detectable but lower amounts of this molecule in their serum, while LEW and SHR rats had little if any present. This molecule probably represents the rat homologue of the murine Q10 gene product, and is the major class I product in the serum of the DA rat strain.

The gene coding for the human T-lymphocyte CD2 antigen is located on chromosome 1p

A cDNA clone encoding the human T lymphocyte sheep erythrocyte receptor [the CD2 (T11) antigen] was used as a probe to define the chromosomal location of the gene. The signal, revealed by hybridisation to Southern blots of genomic DNA from somatic cell hybrids, showed a high degree of concordance for human chromosome 1. In particular, the hybrid F4Sc13C19 which contained the short arm only of human chromosome 1 was positive. The location of the CD2 gene to 1p13 was confirmed by in situ hybridisation.

Human epidermal Langerhans cells cointernalize by receptor-mediated endocytosis "nonclassical" major histocompatibility complex class I molecules (T6 antigens) and class II molecules (HLA-DR antigens)

HLA-DR and T6 surface antigens are expressed only by Langerhans cells and indeterminate cells in normal human epidermis. We have previously demonstrated that T6 antigens are internalized in Langerhans cells and indeterminate cells by receptor-mediated endocytosis. This process is induced by the binding of BL6, a monoclonal antibody directed against T6 antigens. In the present study, using a monoclonal antibody directed against HLA-DR antigens, on human epidermal cells in suspension, we show that the surface HLA-DR antigens are also internalized by receptor-mediated endocytosis in Langerhans and indeterminate cells. Moreover, using immunogold double labeling, we demonstrate that T6 and HLA-DR antigens are internalized through common coated regions of the membrane of Langerhans or indeterminate cells. The receptor-mediated endocytosis that is induced involves coated pits and vesicles, receptosomes, lysosomes, and also, in Langerhans cells, the Birbeck granules. Thus, T6 antigens, which are considered to be "unusual" or "nonclassical" major histocompatibility complex class I molecules, and the major histocompatibility complex class II molecules, HLA-DR, are internalized in Langerhans and indeterminate cells through common receptor-mediated endocytosis organelles.

The induction of class I HLA by interferon-alpha is independent of the cell cycle, but the expression is enhanced by a G1/S block

The induction of class I HLA expression by interferon-alpha (IFN-alpha) was studied in lymphoid cells arrested or traversing different stages of the cell cycle. Exponential cultures of MOLT-4 cells and the MOLT-4 cell variant YHHH were treated with the cell cycle inhibitors aphidicolin and colcemid to obtain cell populations arrested in G1/S and G2/M, respectively, and also cells traversing from S to M and vice versa. Cytofluorimetry with the monoclonal antibody YTH/76.3 (which specifically detects those class I molecules which are most susceptible to IFN-alpha induction) was used to quantitate the class I HLA response to IFN-alpha. The results showed that the response to IFN-alpha is not restricted to a given stage of the cell cycle. These studies also revealed that when the cells were arrested at G1/S, the absolute level of class I HLA expression was enhanced 2-3-fold, both in the presence or absence of either IFN-alpha or IFN-gamma. Therefore, even when absolute levels changed, the ratio of IFN-induced expression to basal expression remained constant at all cell cycle stages. The level of expression of another surface antigen (the CD1 antigen HTA-1) was not affected by the G1/S block. The results were confirmed by dot blot hybridization of poly(A)+ RNA using cDNA-specific probes. These findings suggest that the effect of IFN-alpha is continuous throughout the cell cycle but that a G1-dependent event determines the extent of class I HLA expression, and leads to a synergistic superinduction by IFN in G1/S-arrested cells.

Working principles in the immune system implied by the "peptidic self" model

The hypothesis that self as well as foreign proteins are processed into peptides and presented by major histocompatibility complex antigens leads to a set of working principles that could govern cellular interactions in immune responses. In particular, "idiopeptides," derived from immunoglobulins and T-cell receptors and recognized by appropriate T cells, are expected to play an important regulatory role. We show here that these speculations fit into a consistent view of the immune system.

Isolation of CD1 genes: a family of major histocompatibility complex-related differentiation antigens

CD1 differentiation antigens are defined by a group of monoclonal antibodies that characterize immature human thymocytes. A cloned cDNA has been used to identify CD1 genes in a human genomic library. Five CD1 genes have been isolated, and Southern blot analysis suggests that these represent all the cross-hybridizing human CD1 genes. They share a highly conserved exon, which is homologous to the beta 2-microglobulin-binding domain (alpha 3) of major histocompatibility complex (MHC) class I antigens. In this domain, amino acid sequences are 71-88% homologous. However, the homology between CD1 and MHC class I alpha 3 domains is only 21%. This is the same degree of homology as between either of them and the class II beta 2 domain, which does not bind beta 2-microglobulin. The evolutionary implications of these results are discussed.