Human MHC class II molecules as differentiation markers

A Journey Through Genetics to Biology

Although my engagement with human genetics emerged gradually, and sometimes serendipitously, it has held me spellbound for decades. Without my teachers, students, postdocs, colleagues, and collaborators, I would not be writing this review of my scientific adventures. Early gene and disease mapping was a satisfying puzzle-solving exercise, but building biological insight was my main goal. The project trajectory was hugely influenced by the evolutionarily conserved nature of the implicated genes and by the pace of progress in genetic technologies. The rich detail of clinical observations, particularly in eye disease, makes humans an excellent model, especially when complemented by the use of multiple other animal species for experimental validation. The contributions of collaborators and rivals also influenced our approach. We are very fortunate to work in this era of unprecedented progress in genetics and genomics. Expected final online publication date for the Annual Review of Genomics and Human Genetics, Volume 23 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

An ordered sequence of expression of human MHC class-II antigens during B-cell maturation?

Studies with monoclonal antibodies confirm that human MHC class-II antigens are encoded by at least three pairs of loci. Here Keith Guy and Veronica van Heyningen suggest that as B cells mature theproducts of these loci are expressed in the sequence SB → DR → DC antigens - a sequence which parallels the order of the genes on chromosome 6.

DM influences the abundance of major histocompatibility complex class II alleles with low affinity for class II-associated invariant chain peptides via multiple mechanisms

DM catalyses class II-associated invariant chain peptide (CLIP) release, edits the repertoire of peptides bound to major histocompatibility complex (MHC) class II molecules, affects class II structure, and thereby modulates binding of conformation-sensitive anti-class II antibodies. Here, we investigate the ability of DM to enhance the cell surface binding of monomorphic antibodies. We show that this enhancement reflects increases in cell surface class II expression and total cellular abundance, but notably these effects are selective for particular alleles. Evidence from analysis of cellular class II levels after cycloheximide treatment and from pulse-chase experiments indicates that DM increases the half-life of affected alleles. Unexpectedly, the pulse-chase experiments also revealed an early effect of DM on assembly of these alleles. The allelically variant feature that correlates with susceptibility to these DM effects is low affinity for CLIP; DM-dependent changes in abundance are reduced by invariant chain (CLIP) mutants that enhance CLIP binding to class II. We found evidence that DM mediates rescue of peptide-receptive DR0404 molecules from inactive forms in vitro and evidence suggesting that a similar process occurs in cells. Thus, multiple mechanisms, operating along the biosynthetic pathway of class II molecules, contribute to DM-mediated increases in the abundance of low-CLIP-affinity alleles.

Escape of human cytomegalovirus from HLA-DR-restricted CD4(+) T-cell response is mediated by repression of gamma interferon-induced class II transactivator expression

Human cytomegalovirus (HCMV), a betaherpesvirus, is a pathogen which escapes immune recognition through various mechanisms. In this paper, we show that HCMV down regulates gamma interferon (IFN-gamma)-induced HLA-DR expression in U373 MG astrocytoma cells due to a defect downstream of STAT1 phosphorylation and nuclear translocation. Repression of class II transactivator (CIITA) mRNA expression is detected within the first hours of IFN-gamma-HCMV coincubation and results in the absence of HLA-DR synthesis. This defect leads to the absence of presentation of the major immediate-early protein IE1 to specific CD4(+) T-cell clones when U373 MG cells, used as antigen-presenting cells, are treated with IFN-gamma plus HCMV. However, presentation of endogenously synthesized IE1 can be restored when U373 MG cells are transfected with CIITA prior to infection with HCMV. Altogether, the data indicate that the defect induced by HCMV resides in the activation of the IFN-gamma-responsive promoter of CIITA. This is the first demonstration of a viral inhibition of CIITA expression.

HLA-DR residues accessible under the peptide-binding groove contribute to polymorphic antibody epitopes

Many residues involved in polymorphic antibody-binding epitopes on class II molecules are located on the alpha-helix of DR beta chains. Although they have received less attention, residues in the peptide-binding groove and second domain of the DR beta chain may also be critical for polymorphic anti-DR antibody epitopes. In this study, we used transfectants expressing site-directed mutations at positions in the HLA-DR beta 1 and beta 2 domains and flow cytometry to define the epitopes of several polymorphic anti-DR antibodies. Both DR(beta 1*0403) residues 14 and 25 were shown to be involved in the epitopes of mAbs DA6. 164, HU-20, Q5/6, and 50D6, and DR(beta 1*0701) residue 14 was shown to be critical for the epitopes of two DR7-specific mAbs, SFR 16-DR7M and TAL13.1. Unlike most other residues shown to be important in antibody-binding epitopes, residue 14 is located in the floor of the peptide-binding groove and residue 25 is in an outer loop, each with their side chains pointing down, such that antibodies may directly contact these residues from below the binding groove. Two residues in the beta 2 domain, beta 180 and beta 181, were also shown to be involved in the epitopes of three polymorphic anti-DR mAbs, NFLD.D1, NFLD.M1, and LY9. Although these two residues are close to the transmembrane domain in the linear sequence, their solvent accessibility in the DR1 structures is quite impressive. Our data provide new evidence that residues accessible under the peptide-binding groove contribute to polymorphic antibody-binding epitopes.

A mutant human histocompatibility leukocyte antigen DR molecule associated with invariant chain peptides

From a human histocompatibility leukocyte antigen (HLA)-DR/DQ hemizygous, B lymphoblastoid progenitor, we isolated a cell line, 10.24.6, with a DR alpha missense mutation (96P-->96S), which results in an N-linked carbohydrate addition at position 94 in the DR alpha 2 domain. Several features of 10.24.6 cells suggest that the mutation disrupts normal intracellular formation of peptide/DR complexes. The mutant HLA-DR dimers, though expressed at the cell surface, lack the conformation of the mature, peptide-loaded class II molecules of the progenitor cell, as assessed by their loss of binding of certain antibodies and by the lack of stability in detergent (sodium dodecyl sulfate) solution. In addition, presentation of endocytosed antigen to HLA-DR-restricted T cells is defective in the mutant, but can be restored by transfection of a wild type DRA gene. Assays with synthetic peptides indicate that the 10.24.6 phenotype is not due to an intrinsic inability of the mutant DR molecules to bind peptides. Therefore, to directly evaluate peptide occupancy of the mutant molecules, we analyzed acid-eluted, HLA-DR-associated peptides. The predominant species from the 10.24.6 mutant is a nested set of invariant chain (Ii)-derived peptides that are undetectable in the DR eluate from progenitor cells. The region of DR alpha altered in the mutant molecules is thus implicated in normal formation of peptide/DR complexes. Further, the same set of Ii peptides associated with the DR molecules is present in the eluate from an antigen presentation mutant with a defect in an major histocompatibility complex (MHC)-linked gene. These results suggest that DR molecules in 10.24.6 and in certain presentation mutants are affected at the same or related steps in class II molecule biosynthesis, raising the possibility that class II molecules interact with an MHC-encoded accessory molecule during antigen presentation.

Lack of association of HLA polymorphisms with human papillomavirus-related cervical cancer

An association of HLA-DQ3 with SCC of the cervix has been reported by researchers in Germany and Norway. This article documents a similar-sized study with patients and controls from northwest England. We report in detail on serologically determined HLA polymorphism in SCC patients with respect to HPV 16 infection, MHC class II expression within the tumor, serologic response to HPV, and other relevant clinical variables. We have also extended our studies to include DNA-based analysis using PCR and SSO probes for HLA-DQ. No significant association of any HLA-A, -B, -C, -DR, or -DQ antigen with SCC patients was found. While a possible explanation of the differences among studies could be a reflection of disease heterogeneity, the several tumor and clinical factors examined do not account for the observed differences from previous reports. Further studies are needed for a greater understanding of the interaction of HPV and HLA type in the development of cervical neoplasia.

Identification of residues involved in polymorphic antibody binding epitopes on HLA-DR molecules

Based on previous studies it was predicted that amino acids 4 or 25 of the DR4 beta 1 and DR7 beta 1 chains are involved in polymorphic antibody binding epitopes on DR4 or DR7 molecules. These predictions were tested by analyzing monoclonal antibody (mAb) binding to transfectants expressing mutant DR4 beta 1 or DR7 beta 1 chains with single amino acid substitutions at positions 4 or 25. Antibody binding to transfectants expressing additional DR4/7 beta 1 hybrids was also analyzed to assess further the contributions of four segments of the DR4 beta 1 or DR7 beta 1 chains: amino acids 1-20, 21-40, 41-97, and the beta 2 domain. Single amino acid substitutions at positions 4 and 25 of the DR4 beta 1 chain or DR7 beta 1 chain eliminate binding of several mAb to DR4 or DR7 molecules, documenting that these residues are involved in antibody epitopes. However, the data with the hybrid DR4/7 beta 1 chains indicate that some of these epitopes require contributions from both segments 1-20 and 21-40 of these DR beta chains, whereas other epitopes can be generated by placing the appropriate segment in the context of the other DR beta chain. In addition, the data with other mAb indicate that their epitopes are determined primarily by sequences within the 41-97 segment or in the beta 2 domain.

Candida arthritis: cellular immune responses of synovial fluid and peripheral blood lymphocytes to Candida albicans

A case of septic Candida albicans arthritis of the knee in a patient with systemic candidiasis is presented. Systemic and intra-articular cellular immune responses to C albicans and various bacterial antigens were monitored for 15 weeks. It is shown that the candida induced blastogenesis of synovial fluid lymphocytes was much more stimulated than that of peripheral blood lymphocytes, and that the proportion of activated cells expressing HLA class II antigens was markedly increased in the synovial fluid. Strong cellular immune responses to Candida albicans could still be shown many weeks after the synovial fluid aspirates had become sterile. For the first time synovial fluid derived, CD4 positive T lymphocyte clones with specificity for candida antigens were characterised and further propagated in vitro.

A DR7 specific monoclonal antibody TAL13.1, raised against a transfectant detects IL-4 upregulated antigen on peripheral B-lymphocytes

A monoclonal antibody TAL13.1 was raised against mouse L cells transfected with the human HLA-DRB1*0701 gene. This antibody was found to be polymorphic recognizing a determinant expressed by the DR7, DRB1*0701 and DRB1*0702 gene products. Four polymorphic sites unique to this specificity have been identified within the DR beta 1 domain. These are residues 11-14, 25, 30 and 71-74, one or a combination of which is postulated as being responsible for conferring the specificity of the antibody. In Western blot analysis TAL13.1 was found to react with the DR alpha beta dimer, but not with the free alpha or beta chains. However, in flow cytometry it failed to bind a DR alpha/DQ beta mixed pair transfectant confirming that it recognizes an epitope on the DR beta not the DR alpha chain. Although TAL13.1, a low affinity antibody is negative or only weakly positive on resting peripheral blood lymphocytes (PBLs), we have demonstrated that by interleukin-4 (IL-4) stimulation we can up-regulate the levels of antigen already present and gain a level of binding comparable to that found on B lymphoid cell lines (B-LCLs) where it has been found to be a valuable reagent in their characterization.

Functional analysis of MHC class II-restricted T cells derived from a Caucasian with a DR4, Dw15, DQw8 haplotype

Rabies virus-specific CD4+ T lymphocyte clones were isolated from a Caucasian male vaccine recipient (DR4/7, DQw2/w8; DPw4) and studied for their major histocompatibility complex restricting elements. None of the rabies-specific T-cell clones could be induced to proliferate to antigen by either lymphoblastoid cells or DR-transfected L cells expressing DR4 molecules of the Dw subtypes commonly found on Caucasian individuals (Dw4, Dw10, Dw13, Dw14). The HLA-Dw subtype of the rabies vaccine recipient was determined by conventional mixed lymphocyte culture, and the results revealed that this individual had a DR4 (Dw15), DR7 (Dw7) phenotype. The presence of the DR4, Dw15 antigen was confirmed by nucleotide sequencing of the DR4B1 gene corresponding to the DRB1*0405 allele. Significant antigen-induced T-cell proliferative responses were obtained with two DR4, Dw15, DQw4 homozygous lymphoblastoid cell lines of Japanese origin (HAS-15 and KT-3) and with a L-cell transfectant expressing the DR4, Dw15 molecule. The existence of the DR4, Dw15 antigen in the Japanese has been reported to be associated with the DQw4 specificity. However, the presence of DQw8 (previously designated DQw3.2) and the absence of DQw4 in the lymphoblastoid cells of the Caucasian rabies vaccine was confirmed with monoclonal antibodies IVD12 (anti-DQw7 + DQw8 + DQw9) and HU46 (anti-DQw4) and by the reactivity of a DQw8-restricted antigen-specific T-cell clone. These studies indicate, contrary to previous findings, that the DR4, Dw15 molecule may be present in Caucasian (non-Japanese) individuals in association with DQw8.

Antigen-presenting cells in the skin and placenta in pemphigoid gestationis

In pemphigoid gestationis (PG), one of the major initiating events is the aberrant expression of the class II molecules of the major histocompatibility complex in the placenta. We used a panel of 13 monoclonal antibodies to investigate the phenotype of the MHC class II positive antigen-presenting cells (APC) in the skin and placenta in PG. In the skin, the APC show reactivity with a variety of macrophage markers and the CDI marker of Langerhans cells. By contrast, the MHC class II positive cells in the placenta showed no reactivity with macrophage or Langerhans cell markers, but were the cytokeratin-positive trophoblast or vimentin-positive stromal cells.

Human memory T cells express intercellular adhesion molecule-1 which can be increased by interleukin 2 and interferon-gamma

We have shown that low levels of intercellular adhesion molecule-1 (ICAM-1) expression can be detected on approximately 40% of the resting peripheral blood T cell population. The ICAM-1+ T cells have the phenotypic markers of memory cells which can be distinguished functionally from naive T cells by their ability to respond rapidly to previously experienced antigen. These cells appear to be in a state of marginal activation in that they also express low levels of the interleukin 2 receptor (Tac antigen) and have increased cell size as compared to the naive T cells. In addition we have shown that the cytokines interleukin 2 and interferon-gamma, both of which are products of activated T cells, are able to increase the expression of ICAM-1 on T cells. Finally, pretreating T cells with an anti-ICAM-1 monoclonal antibody inhibits their response to recall antigens, strongly suggesting a functional role for this protein on the memory T cell.

Salmonella-reactive synovial fluid T-cell clones in a patient with post-infectious Salmonella arthritis

From a patient with reactive arthritis following Salmonella typhimurium enteritis, synovial fluid T-lymphocytes were cloned and expanded in vitro. Seven out of 74 clones showed a marked proliferative response to antigens of heat-killed Salmonella typhimurium with autologous T-cell-depleted peripheral blood mononuclear cells as antigen-presenting cells. The Salmonella-reactive clones were of the CD4+ phenotype, antigen-induced proliferation could be inhibited by a monoclonal antibody to HLA class II. One clone recognized both Salmonella and Campylobacter jejuni antigens in the proliferation assay. The multiclonality of Salmonella-reactive synovial fluid T-cells indicates that the microorganisms have been present, at least transiently, within the affected joint and thus recruited specific T-lymphocytes that might initiate synovitis.

Immunopathology of the placenta in pemphigoid gestationis and linear IgA disease

We have investigated the immunopathology of the placenta in bullous diseases by studying the deposition of immune complexes and expression of MHC class II subregion products by immunohistological methods. Placentae from seven patients with pemphigoid gestationis (PG) and two patients with linear IgA disease were studied. In PG immune complexes containing IgGI and C3 were identified in six cases. In linear IgA disease IgAI containing immune complexes were found in both cases. Placentae from patients with PG showed aberrant expression of MHC Class II products. This was not seen in the placentae from patients with linear IgA disease. In PG there was incoordinate expression of the subregion products, DP and DR being more extensively and consistently expressed than DQ. These results and previous immunogenetic studies suggest that PG may be unique among organ specific autoimmune disease, the autoantibodies forming during an allogenic response rather than target cells behaving as antigen presenting cells.

Differential expression of CD25 and HC2 antigens on subtypes of acute myeloid leukemias

The presence of CD25 and HC2 antigens in 66 different patients with acute myeloid leukemia (AML) was investigated. The expression of both antigens was observed in 32% of AML cells. Dual fluorescence staining experiments performed in 5 AML patient cells showed that CD25 and HC2 antigens were simultaneously expressed in a single cell. The expression of both antigens was mainly observed in the M4 and M5 subtypes of AML. Although immunopurified IL-2 was able to block the binding of anti-CD25 monoclonal antibody to the AML cells, the IL-2 receptor did not appear to be functional.

Class II MHC expression in normal adrenal cortex and cortical cells in autoimmune Addison's disease

It has been proposed that aberrant expression of class II major histocompatibility complex (MHC) molecules by target cells may be an initiating factor in some forms of organ specific autoimmunity. This hypothesis was tested in relation to the autoimmune form of Addison's disease by studying autopsy adrenal glands from eight patients who had died of recent onset idiopathic Addison's disease. Using an immunohistochemical technique, class II MHC expression was found in a minority of adrenal cortical cells in the zona reticularis in 25 normal and four hyperplastic glands, while in Addison's disease almost all residual cortical cells expressed class II MHC. Three tuberculous adrenals showed increased staining of cortical cells around areas of chronic inflammation. It is concluded that since adrenal cortical cells of the normal gland express class II MHC, aberrant expression of this product cannot be invoked as an initiating mechanism in autoimmune adrenalitis. The increased cortical expression of class II MHC seen in idiopathic Addison's disease and tuberculosis may be due to local release of lymphokines by inflammatory cells.

Analysis of HLA-DR glycoproteins by DNA-mediated gene transfer. Definition of DR2 beta gene products and antigen presentation to T cell clones from leprosy patients

We have used DNA-mediated gene transfer to express HLA class II molecules in mouse L cells for serological, biochemical, and functional analysis. cDNA clones encoding the DR2 beta a and DR2 beta b products of the DR2Dw2 haplotype were subcloned into a mouse Moloney leukemia virus-based expression vector (pJ4) and transfected separately into mouse L cells together with a HLA-DR alpha/pJ4 construct. These transfectants have allowed differential analysis of the two DR2 beta products in a manner normally prohibited by the concomitant expression seen in B cells. Two-dimensional SDS-PAGE analysis of the transfectants defines the more acidic beta chain as the product of the DR2 beta a sequence, and the more basic chain as the product of the DR2 beta b sequence. The LDR2a transfectants present antigen efficiently to M.leprae-specific T cell clones and are capable of presenting synthetic peptide, 65-kD recombinant mycobacterial antigen and M.leprae. Of the DR2Dw2-restricted T cell clones we have tested, all use the DR2 beta a chain as their restriction element. Inhibition studies with mAbs demonstrate the dependence of presentation by the transfectant on class II and CD4, while mAbs against LFA-1, which substantially inhibit presentation by B-lymphoblastoid cell lines, do not inhibit transfectant presentation.

Quantitative immunological differences between newly diagnosed Graves' disease patients and relapsed patients

Class 2-positive T cells, T-cell and mononuclear cell subsets, thyrotropin receptor antibodies (TRAb) and immune complexes were evaluated in 34 newly diagnosed Graves' patients and in 13 relapsed patients before a cycle of specific medical treatment. Class II-positive T lymphocytes were detected by monoclonal antibodies against different epitopes of class II antigens, whereas 4F2-positive cells were detected by 4F2 monoclonal antibody. 4F2-positive cells were statistically increased in newly diagnosed Graves' patients compared to relapsed patients (p less than 0.05). An increased percentage of class II activated T cells, detected by monoclonal antibodies L243, was found in newly diagnosed patients in comparison with relapsed subjects (p less than 0.025). Newly diagnosed Graves' patients showed a significant decrease in the ratio suppressor/cytotoxic T cells in comparison with normal control subjects but not with relapsed patients. Ninety-one % of newly diagnosed Graves' patients showed a high TRAb value, whereas only 69% of relapsed patients showed increased values (p less than 0.025). No difference was observed in the immune complex positivity between newly diagnosed Graves' patients and relapsed subjects. In conclusion, both humoral and cellular immune differences were found in relapsed patients vs newly diagnosed Graves' patients. The immunological abnormalities are quantitatively more pronounced in the latter group.

Monoclonal antibodies to sheep MHC class II molecules recognize all HLA-D or subsets of HLA-D region products

Six murine monoclonal antibodies raised against sheep MHC class II molecules were analyzed for reactivity with HLA-D subregion products. All the antibodies reacted with human peripheral blood lymphocytes, monocytes, and B-lymphoblastoid cell lines homozygous for various HLA-DR specificities, suggesting that the antibodies recognized nonpolymorphic determinants on HLA class II molecules. SDS-PAGE and two-dimensional NEPHGE/SDS-PAGE analyses of molecules immunoprecipitated from 35S-methionine-labeled, DR-homozygous B-lymphoblastoid cell lines showed that the monoclonal antibodies precipitated typical class II molecules (Mr 32-34K and 25-29K). From comparison with antibodies of known HLA-D subregion specificity, two of the sheep antibodies appeared to react with the products of single HLA-D subregions, while another showed balanced reactivity with all HLA-D molecules. Antibody SBU.II 38-27 reacted exclusively with HLA-DQ molecules, antibody SBU.II 28-1 with HLA-DP molecules, and antibody SBU.II 49-1 with HLA-DR, -DQ, and -DP molecules. However, analysis of immunoprecipitates from surface-iodinated WT-49 cells (DR3 homozygous) using SBU.II 28-1 and the DP-specific monoclonal antibody B7/21, suggested that the two antibodies immunoprecipitated different alpha polypeptides. The two antibodies SBU.II 38-27 and 28-1 appear to be at least as specific as existing reagents, if not more so. As such, they are of value in their potential contribution to our understanding of the molecular characteristics and ultimately the functions of the HLA-DQ and -DP subregion products, as well as the identification/characterization of HLA-D equivalents in other species.

Sequence and evolution of HLA-DR7- and -DRw53-associated beta-chain genes

cDNA clones representing products of the DR7 and DRw53 beta-chain genes were isolated from the human B-lymphoblastoid cell line MANN (DR7,DRw53,DQw2, DPw2). The DRw53 beta sequence was identical to a DRw53 beta sequence derived from cells with a DR4 haplotype. In contrast, the DR7 beta sequence was as unrelated to DR4 beta sequence as it was to other DR beta-related genes, except at the 3'-untranslated region. These results suggest that the DR7 and DR4 haplotypes may have been derived relatively recently from a common ancestral haplotype and that the DR4 and DR7 beta-chain genes have undergone more rapid diversification in their beta 1 domains, most probably as a result of natural selection, than have the DRw53 beta-chain genes. Short tracts of sequence within the DR7 and DRw53 beta 1 domains were shared with other DR beta sequences, indicating that exchanges of genetic information between beta 1 domains of DR beta-related genes have played a part in their evolution. Serological analysis of mouse L-cell transfectants expressing surface HLA-DR7 molecules, confirmed by antibody binding and allelic sequence comparisons, identified amino acid residues that may be critical to the binding of a monomorphic DR- and DP-specific monoclonal antibody.

Reactivity of human trophoblast with an antibody to the HLA class II antigen, HLA-DP

Cytotrophoblast cells in term amniochorion and in first trimester chorionic villi were shown by immunohistology of frozen tissue sections to bind B7/21, an antibody specific for the MHC Class II antigen, HLA-DP. This binding was shown to be specific, as adsorption of the B7/21 antibody with a B cell line expressing HLA-DP prevented subsequent binding to trophoblast. When tested with a variety of other antibodies reacting with HLA-DR, HLA-DQ or the common sequences of HLA-DR, -DQ and -DP, trophoblast was negative, thus confirming previous reports. The significance of this unique pattern of reactivity of trophoblast is discussed.

Major histocompatibility complex class II antigen expression in B and T cell non-Hodgkin's lymphoma

An immunohistochemical study of 46 B and T cell non-Hodgkin's lymphomas, using monoclonal antibodies to the products of the major histocompatibility complex (MHC) class II antigen subregions, DP, DQ, and DR, showed that most B and T cell lymphomas express these antigens. Both coordinate and non-coordinate expression of MHC class II antigens was observed, but this did not correlate with immunological phenotype, morphological grade, or proliferation index as determined by flow cytometry.

Expression of HLA-D sub-region products on human colorectal carcinoma

The major histocompatibility complex (MHC) status of normal, inflamed, pre-malignant and malignant epithelia of the human gastrointestinal tract was investigated by immunocytochemical methods using monoclonal antibodies (MAbs) directed against heavy (alpha)- and light (beta 2m)-chain Class-I molecules and sub-locus products (DP, DQ, DR) of the HLA-D region. Class-I expression on epithelial cells appeared to vary little with pathological status except in the case of 4/32 (13%) colorectal carcinomas in which the antigens were undetectable or scanty. The pattern of Class-II expression was more complex. The antigens were readily detectable on normal stomach epithelium, in villous adenomas and in inflammatory bowel mucosa. In each of these situations DR was the predominant specificity, followed by DP and DQ. Expression on normal colonic epithelium was usually negative but, in the vicinity of a neoplasm or an area of marked leukocyte infiltration, Class-II molecules (DR greater than DP much greater than DQ) were detectable. A similar pattern of non-coordinate expression was found on 23/32 (72%) colorectal carcinomas, but on the remaining 28% no Class-II products were detectable, under conditions wherein stromal leukocytes were strongly stained. The data suggest that in a significant proportion (nearly 30%) of primary colorectal carcinomas, the capacity for Class-II induction, a constitutive or acquired feature of normal colorectal epithelium, is either diminished or lost. Also, tumor Class-II status is not correlated to Dukes' stage or differentiation.

Expression of MHC class II products on human colorectal cancer. An immunohistological and flow cytometric study

The MHC status of epithelial cells from 32 primary colorectal neoplasms, villous adenomata (VA; 2) and inflammatory bowel disease (IBD; 3) were evaluated using a panel of monoclonal antibodies (mAbs). Class I antigens and beta 2 microglobulin (beta 2m) were expressed on all normal, benign, inflammatory and malignant epithelia with the exception of two carcinomas. A more complex pattern of reactivity was encountered with anti-class II mAbs. Some expression was detected on normal glandular and luminal epithelium, particularly adjacent to the tumour. Inflammatory tissues, VA and 23/32 carcinomas were also antigen-positive, the proportion of stained epithelial cells ranging from 5% to 90%. Expression was usually non-coordinate, DR being the predominant specificity followed by DP and DQ, which is suggestive of independent D region gene regulation. The hypothesis that class II expression is induced in vivo by locally generated IFN gamma was not confirmed by in vitro treatment with this agent of epithelial colorectal carcinoma-derived cell lines. These provisional data suggest that although IFN gamma may be a necessary stimulus for class II expression it is insufficient and that other factors also influence the responsiveness of tumour cells in this respect.

Expression of MHC class II antigens in human B-cell leukaemia and non-Hodgkin's lymphoma

In this review we have summarized our experiences of serological analysis of MHC class II antigen expression in human B cell malignant disease. Cells from a large number of cases of B-cell chronic lymphocytic leukaemia (CLL) and non-Hodgkin's lymphoma (NHL) have been examined for expression of class II antigens. Using a number of monoclonal antibodies which in some cases are specific for class II subregion products (DP, DQ and DR), MHC class II antigens were detected by indirect immunofluorescence and fluorescent activated cell sorter analysis in CLL and by immunohistochemical staining in NHL. At the cell surface in many cases of B cell malignant disease, products of the different class II subregion genes are non-coordinately expressed. The most commonly occurring pattern of non-coordinate expression of class II molecules is of expression of DP and DR antigens in the absence of detectable DQ expression. These findings are in contrast to normal B lymphocytes where DP, DQ and DR antigens are expressed together at the cell surface. There is considerable heterogeneity among cases comprising individual histopathological categories of B cell malignancy, and in many instances heterogeneous class II phenotypes are also found on cells from the same tumour. In chronic lymphocytic leukaemia, class II antigen expression is inducible in vitro by treating the cells with the phorbol ester TPA. CLL cells treated with TPA have much increased levels of class II antigen expression at the cell surface and much increased steady state levels of class II specific mRNA transcripts detectable with complementary DNA probes. Aberrant class II antigen expression may be involved in the pathogenesis of B cell malignant disease.

Distribution of class IIDQ antigens on normal and leukemic lymphoid cells

The distribution of DQ as well as DR antigens was examined on lymphoid and monocytic cells at different stages of differentiation. In the B cell series, both immature and differentiating (under Staphylococcus aureus or pokeweed mitogen stimulation) B cells often lacked DQ molecules; among surface IgM+ and IgD+ cells, both DQ and DR molecules were detected except on cells from 30% of the lymphoid malignancies studied. T cells expressed DQ molecules only after stimulation; a DQ-DR+ phenotype was observed in a large number of cells after allogeneic stimulation, in certain antigen-specific T cell lines as well as in T cell lymphomas, suggesting that class II antigens had a distinct pattern of regulation. In the monocytic lineage, DQ molecules were expressed by most lymph node monocytes and only a low percentage (20%) of circulating monocytes.

Differential expression of HLA-DR and HLA-DQ antigens on normal cells of the myelomonocytic lineage

We have previously shown that HLA-class II antigens have a differential expression on acute myeloblastic leukaemia (AML) blasts. These cells express HLA-DR molecules but the HLA-DQ antigens are undetectable. In this paper we study the expression of HLA-DR and HLA-DQ antigens, using monoclonal antibodies (MoAbs), on normal cells of the myelomonocytic lineage: the common myelomonocytic progenitor (CFU-GM) and the monocytes, by techniques of inhibition of CFU-GM growth and double immunofluoroscence, respectively. The results show that HLA-DR and HLA-DQ antigens are differentially expressed on normal myelomonocytic cells. While HLA-DR molecules are expressed on CFU-GM and on the majority of peripheral blood monocytes, HLA-DQ antigens are not expressed on CFU-GM and only present on a subpopulation of monocytes. This data further confirms that HLA-DR and HLA-DQ molecules are coded by different genes with independent regulation of the gene expression not only on myeloid leukaemias but also on normal cells of the myelomonocytic lineage.

Monoclonal antibodies against human Ia antigens stimulate monocytes to secrete interleukin 1

The monoclonal antibodies (mAb) DA6.147, DA6.164, and HIG.48 against human Ia antigens, but not the W6/32 mAb against human class I major histocompatibility complex antigens or the anti-monocyte OKM1 and 63D3 mAb, stimulated monocytes to secrete interleukin 1 (IL-1). IL-1 was measured by its property of promoting the production of interleukin 2 (IL-2) by phytohemagglutinin-treated LBRM-33 clone 1A5 cells. IL-1 activity induced by anti-Ia antibodies could be detected 24 hr after initiation of the cultures and reached its highest levels at days 3-4 of culture. Concentrations of 1 microgram/ml or higher of the anti-Ia antibodies induced monocytes to secrete significant levels of IL-1 activity. The anti-Ia mAb induced Ia-bearing but not Ia-negative monocytes to secrete IL-1. Both Ia-positive and Ia-negative monocytes produced IL-1 activity under the stimulus of lipopolysaccharide. It is concluded that the DA6.147, DA6.164, and HIG.48 mAb stimulate secretion of IL-1 by interacting Ia antigens on monocytes. The data support the view that besides serving as restricting elements for recognition of foreign antigens by T cells, Ia antigens may also function as transducer elements.

Homozygous typing cell-defined HLA-Dw specificities correlate better than serologically defined HLA-DR specificities with restriction elements for influenza virus-specific proliferative human T lymphocyte clones

Human T lymphocyte clones with specific proliferative response to influenza A virus were derived by limiting dilution from peripheral blood lymphocytes (PBL) after in vitro stimulation with autologous irradiated, virus-infected PBL. Four OKT3+4+8- T lymphocyte clones (TLC) that showed HLA-restricted antigen-specific proliferative responses were used for a detailed analysis of the restriction elements for antigen presentation. None of the clones showed alloreactivity and all required the presence on the antigen-presenting cell of HLA class II antigens of one or other haplotype of the donor. Restriction elements for two clones were correlated with Dw1 rather than DR1, and for two others with Dw6 rather than DRw6. These latter clones showed differential recognition of HLA-Dw6 subtypes as defined tentatively by homozygous typing cells, without relationship to putative serological "splits" of DRw6. One of the Dw6-restricted clones was specific for a Dw6.1 (now Dw18) "subtype," confirmed by family segregation analysis, the other for a broad Dw6 (Dw18 and Dw19) specificity. Studies with a panel of monoclonal antibodies against monomorphic determinants of HLA class II antigens revealed heterogeneous patterns of blocking activity, distinguishing between clones of different restriction specificity. Inhibition patterns were partly as predictable from the known activity of the monoclonal antibody in alloantigeneic PLT systems. These results provide evidence that certain structures that function as restriction elements for antigen presentation also carry alloantigeneic determinants.

HLA-DR expression in a human colonic carcinoma cell line

A human colonic carcinoma cell line (HCA-7) isolated from a well differentiated mucoid adenocarcinoma of the colon has been maintained in vitro for 3 years. It spontaneously synthesizes HLA-DR which is mainly intracytoplasmic. Stimulation with lymphocyte conditioned medium and recombinant gamma-interferon results in enhanced synthesis of HLA-DR and the appearance of the antigen on the cell surface. A dose response study showed that maximal stimulation of the culture was achieved with 50 units/ml of recombinant gamma-interferon. Staining for HLA-DR was uneven being confined to focal areas of the monolayer, which is similar to the focal expression of HLA-DR seen in sections of adenocarcinoma of the colon. The functional significance of this phenomenon is unclear, but it may explain the presence of lymphoid infiltrates in tumours.

Implication of structural class II gene polymorphism for the concept of serologic specificities

We have used DNA-DNA hybridization methods to study the relationship of genetic polymorphisms to the established HLA-D region determinants as detected with serological reagents. The supertypic determinants DRw52 and 53 are closely associated with a particular RFLP detected with the DR beta probe, but are seemingly encoded by a distinct beta gene compared to the "conventional" DR antigens. DQw1 is closely associated with a DQ alpha chain polymorphism, whereas the DQw2 and 3 specificities have correlations to RFLP using the DQ beta probe. Additional DQ polymorphism, in linkage disequilibrium with DR but yet without a serological counterpart is also described. Considering the finding that there exist a varying number of DR beta genes in different DR haplotypes (Böhme et al. 1985), from 1 in DRw8 to 3 (or 4) in DR4- and DR7-positive cells, we have made a tentative re-evaluation of the genetic basis for the conventional DR specificities. The combination of cell surface antigens encoded by DR and DQ loci are believed to form the basis for MLC stimulating determinants. We have speculated that a combination of determinants encoded by distinct DR beta genes and in certain instances additional DQ polymorphism is responsible for the DR types. Thus, only a limited variability is observed after DNA-DNA hybridization using DR beta probes. Only DR1-, 2- and 4-positive cells have distinct bands not detected in any other haplotypes, whereas DR3, 5, w6, and w8 can be characterized by a combination of bands, which is the result of hybridization with several DR beta genes. Furthermore, we have suggested that the difference between the DR3 and DRw6 specificities is due to variability with regard to 1 DQ beta gene, and have also made the assumption that DRw6 cells may express a lower concentration of DR locus encoded products compared to DR3-positive cells (Haziot et al. 1985). In addition, we have discussed the genetic basis for so-called DR blanks, implying that an unorthodox combination of DR and DQ determinants forms the basis for difficulties in assigning DR types to such cells in some cases and that "blanks" can be associated with low expression at the cell surface of well-known DR determinants. The use of cDNA and genomic probes for distinct class II genes to elucidate the mechanisms of HLA and disease association has been documented and discussed.

Specificity of monoclonal antibodies directed against human and murine class II histocompatibility antigens as analyzed by binding to HLA-deletion mutant cell lines

The specificity of 70 monoclonal anti-Ia monoclonal antibodies (MoAbs) (18 mouse allo-induced and 52 rodent anti-human) was studied with a panel of 17 HLA-deletion mutants that were derived from a single parent line and vary in expression of Ia antigens due to deletion of different subregions of HLA. MoAb binding was analyzed both by ELISA and flow microfluorometry. Characterization of the MoAbs with respect to specificity for products of subregions of a DR1-DC1-SB2 haplotype revealed great complexity. Many antibodies were quite specific for DR-linked determinants (26 MoAbs), DC-linked determinants (5 MoAbs), or determinants indistinguishable from SB (4 MoAbs). However, many MoAbs bound to products of more than one subregion: DR + SB (+/- weak DC) (22 MoAbs); DR + DC (3 MoAbs); or DR + DC + SB (1 MoAb). Furthermore, a number of the MoAbs bound unequally to products of the two HLA haplotypes analyzed, particularly among those recognizing DC1-linked determinants and the murine alloinduced MoAbs. Finally, despite strong structural homologies of murine I-A to human DC and murine I-E to human DR, the intraspecies cross-reactions of MoAbs do not closely follow that pattern. These data: (1) illustrate the usefulness of HLA-deletion mutant cell lines for analysis of the specificity of MoAbs and for delineation of HLA subregions; (2) demonstrate the great diversity of MoAbs specific for class II molecules and the high frequency of MoAbs that bind to products of more than one Ia subregion, particularly DR and SB. In view of such complexity, many (perhaps most) MoAbs cannot be relied on to unambiguously identify products of a particular Ia subregion, without extensive characterization.

Immunohistochemical analysis of human MHC class II antigens in B-cell non-Hodgkin's lymphomas

Twenty cases of B-cell non-Hodgkin's lymphoma (NHL) were evaluated by immunohistochemical staining of frozen sections with a panel of anti MHC class II monoclonal antibodies (MCA). These studies showed marked differences in the expression of class II antigens both between different cases and within the population of cells of individual cases. In all of the cases studied the majority of the tumour cells reacted with MCAs directed against determinants common to the products of SB and DR loci. However, MCAs specific for DC determinants failed to react with 3/20 cases and in several other cases stained only a minority of cells. Absent or reduced expression of DC antigens was most marked in lymphocytic lymphoma; however, in centroblastic-centrocytic and centroblastic lymphomas, DC antigens could be detected on the majority of cells.

Activation of human T lymphocytes II. Involvement of the T3 antigen in polyclonal T cell activation by mitogenic lectins and oxidation

The effect of monoclonal antibodies against the T cell surface antigens T3 and T4 on accessory cell-dependent mitogen-induced proliferation of human antigen-specific T4+ T lymphocyte clones and purified peripheral blood T cells was studied. To avoid the Fc receptor-dependent mitogenic effects of the OKT3 antibodies, monocytes were replaced by Epstein-Barr virus-transformed B lymphoblastoid cells as accessory cells. Monoclonal antibody OKT3 but not OKT4 inhibited the response of both T lymphocyte clones and purified T cells to mitogenic lectins and oxidation. The inhibition was not due to nonspecific effects of the monoclonal antibodies since it affected only the initial triggering but not the proliferation of activated T cells and it could be overcome by higher concentrations of lectin indicating a competition between OKT3 antibody and lectin. Furthermore, OKT3 antibody at the same concentration that was inhibitory in this system was mitogenic in the presence of Fc receptor-bearing monocytes. Surface modulation of T3 but not of T4 antigens led to unresponsiveness to a mitogen pulse given directly after modulation. These findings suggest that antigen-specific and mitogen-induced T cell triggering are due to interaction with the same receptors of the T lymphocyte.

T-cell proliferation and expression of MHC class II antigens

Two monoclonal antibodies to major histocompatibility complex (MHC) class II antigens, which in combination identify beta chains encoded by the SB and DR loci, were used to investigate which of these gene products were expressed at the cell surface of unstimulated T cells and at various stages of mitogen-induced T-cell maturation. In tests on blood lymphocytes from healthy donors 12% of T cells expressed class II antigens, but only SB antigens were expressed. During activation of T lymphocytes, SB-coded antigens were expressed before DR antigens, and the kinetics of SB expression correlated with the proliferative response of T cells. These results and consideration of recent reports from other laboratories lead us to suggest that SB-coded class II antigens play a role in T-cell proliferation.

Delineation of serologically distinct monomorphic determinants of human MHC class II antigens: evidence of heterogeneity in their topographical distribution

Three monoclonal antibodies (mAbs), FMC4, FMC14 and FMC15, which react with invariant sites of major histocompatibility complex (MHC) class II (Ia-like) molecules were studied in various serological assays. Sequential immunodepletion experiments show that all three epitopes are present on the same class II molecules. However, a minor subset may exist which does not express epitope 15. In competitive binding assays, using several different B-lymphoblastoid cell lines (B-LCLs), e.g. BRISTOL-8 8392, B-85, RAJI, 8866, CESS-B and LD-B, FMC4 did not block the binding of FMC14, or FMC15, and vice versa. In contrast, mutual inhibition was observed between FMC14 and FMC15. Furthermore, pairwise combinations of saturating amounts of FMC4 + FMC14 and FMC4 + FMC15 gave additive binding whilst FMC14 + FMC15 did not. These results demonstrate that epitopes 4 and 14/15 are spatially distinct; 14 and 15 on the other hand appear to be spatially related. However, contrary to this partial and reciprocal inhibition was consistently observed between FMC4 and FMC14 on two other LCLs, namely DAUDI and BALM-2. Furthermore, on certain cells, FMC14 and FMC15 show markedly disparate binding. Taken together, these observations indicate that the juxtaposition of certain epitopes on class II antigens can vary according to the cell type. This demonstrates a hitherto unreported heterogeneity of antigenic determinants and of their topographical distribution on the class II molecule.

Intra-epithelial lymphocytes in the normal epididymis. A mechanism for tolerance to sperm auto-antigens?

Using a monoclonal immunoperoxidase technique on frozen tissue sections of normal testis and epididymis, a distinctive distribution of lymphocytes has been identified. Almost all of the intra-epithelial lymphocytes were T cells and the majority of these belonged to the T8+ ("suppressor/cytotoxic") subset. The distribution contrasted with the predominance of the T4+ ("helper/inducer") subset in the interstitial tissues and in normal peripheral blood. The predominance of the "suppressor/cytotoxic" subset within the epithelium of the epididymis may exist in order to prevent the development of the immune response to auto-antigens on spermatozoa.

Functional characteristics and differential expression of class II DR, DS, and SB antigens on human melanoma cell lines

Although most cultured melanoma cell lines express DR Class II molecules, many of these do not also express the DS (MB) Class II molecules as detected by a monoclonal antibody specific for DS. Cells lacking either DR or DS molecules or both could only be induced to express DR antigens in rare cases by combined incubations with azacytidine and Interleukin-2 conditioned medium, although the expression of DR molecules on fibroblasts or U937 monocytes could more easily be induced under the same culture conditions. Melanoma cells expressing DR antigens could function in antigen presentation for the histocompatibility antigens themselves and for DR specific presentation of TNP determinants to allogeneic T-cells sensitized to TNP modified lymphocytes and showing restriction in their responses to the specificity of the DR molecules expressed on the original, autologous sensitizing cells. DR positive melanoma cells could not, however, be demonstrated to function in the presentation of any of the soluble antigens tested. All DR positive melanoma cells also expressed SB antigens, but these were not detected on DR negative melanoma cells. These studies collectively indicate that the expression of Class II histocompatibility antigens on diverse cell types is subject to differential regulatory control and is associated with differences in their functional activities.

Activation of human T lymphocytes I. Requirements for mitogen-induced proliferation of antigen-specific T lymphocyte clones

In a model system for accessory cell (AC)-dependent mitogen-induced T cell proliferation the response of several human antigen-specific HLA-restricted helper T lymphocyte clones (HTLC) to mitogens was studied. It was found that the HTLC themselves did not or only weakly respond to various mitogens or to oxidation by galactose oxidase, but that the response could be strongly increased if certain tumor cell lines were added to the assay as AC. Pretreatment with lectins or oxidation of either HTLC or AC was effective in stimulating the proliferation of the T cells in this system. Reduction of the aldehydes formed during oxidation completely abolished the stimulatory activity of oxidized B lymphoblastoid cell line. This shows that cross-linking of T cell and AC is required to induce proliferation. When several established cell lines were tested for their capacity to function as AC in this system, profound differences in AC activity were detected. The inability of cells with poor AC activity to stimulate the HTLC was not due to trivial reasons, such as requirements for different mitogen concentrations, a decreased binding of mitogens or suppressive effects. Furthermore, AC activity was not dependent on the presence of Ia antigens on the AC. These findings are discussed with regard to the mechanism of mitogen-induced T cell activation.

Quantitation of dendritic cells in normal and abnormal human epidermis using monoclonal antibodies directed against Ia and HTA antigens

Two monoclonal antibodies, NAI 34 and DA6 231, have been used as surface markers to count epidermal Langerhans cells in normal skin, allergic contact dermatitis, and mycosis fungoides of the plaque and poikilodermatous varieties. The antibodies recognized the HTA (human thymocyte antigen) and Ia antigens, respectively. In all situations the numbers of cells labeled by the two antibodies differed. In normal skin 75% of dendritic cells were labeled by both antibodies and 25% were labeled by NAI 34 alone. In contact dermatitis there is an increase in dendritic cells labeled by both antibodies and this pattern is also seen in untreated plaque stage mycosis fungoides. In poikilodermatous mycosis fungoides, striking staining of the epidermal keratinocytes with DA6 231 is seen with no dendritic cells labeled. Dendritic cells are, however, clearly seen with NAI 34 staining. Numbers of dendritic cells labeled by both antibodies fall during PUVA therapy.

Monoclonal antibodies against HLA-DR antigens replace T helper cells in activation of B lymphocytes

In the presence but not in the absence of pokeweed mitogen (PWM), monoclonal antibodies against HLA-DR antigens 147 and 164 helped highly purified B lymphocytes to proliferate and mature to Ig-secreting cells. In contrast, neither anti-DR antibody 231 nor the UCHT1 monoclonal anti-human T cell antibody (both of the same isotype as the 147 and 164 anti-DR antibodies) exhibited any helper activity on B cells. B cells pulsed with PWM and subsequently cultured in the presence of anti-DR antibody 147 or 164 proliferated and secreted Ig, whereas B cells that first were pulsed with antibody 147 or 164 and then incubated with PWM did not. PWM alone did not induce any of these responses on purified B cells. Also, antibodies 147 and 164 significantly increased the number of Ig-secreting cells obtained from the WT51 Epstein-Barr virus-transformed B-cell line. Anti-DR antibody 231 inhibited the helper activity on WT51 cells mediated by anti-DR antibody 164. Finally, anti-DR antibodies 147 and 164 assisted B cells from the spleen of athymic nu/nu mice (which bear I-E-encoded products) to produce IgM antibodies against sheep erythrocytes. However, these antibodies had no effect on mouse B cells which do not express on their surface I-E-encoded Ia antigens. Taken collectively, these findings suggest that the structures detected by anti-DR antibodies 147 and 164 on B lymphocytes function as acceptors/transducers of T-cell-derived helper signals.

Enhanced expression of human Ia antigens by chronic lymphocytic leukemia cells following treatment with 12-O-tetradecanoylphorbol-13-acetate

Using a panel of monoclonal antibodies which detect framework determinants of human-Ia alpha and beta polypeptides and the DC-specific monoclonal antibody Genox 353, the in vitro effects of 12-O-tetradecanoylphorbol-13-acetate (TPA) on the expression of Ia antigens by cells from chronic lymphocytic leukemia (CLL) patients have been studied. In all subjects studied a great increase in expression of framework Ia determinants was found following culture of CLL cells for 90 h with TPA at 10(-7) g/ml. TPA treatment of CLL cells also induced increased expression of Genox 353+ antigens, in some cases where Genox 353 binding was either negligible or not detectable in cells cultured in the absence of TPA.

An HLA-DR negative acute leukaemia which stimulates MLC and CMC responses

We describe an acute myelomonocytic leukaemia (E72) devoid of cell-surface HLA-DR antigens, but capable of inducing cellular responses. Leukaemia E72 induced proliferation of normal lymphocytes in primary mixed lymphocyte culture (MLC), which was only weakly inhibited by anti-DR sera. Depletion of a small percentage (congruent to 4%) of DR+ cells on a cell-sorter failed to abrogate the capacity of E72 to stimulate MLC and cell-mediated cytotoxicity (CMC) responses. We found that normal lymphocytes primed with E72 responded in secondary MLC to lymphocytes and leukaemias, suggesting that the lymphocyte-activating determinant (LAD) on E72 is not leukaemia-specific. In addition, E72 induced CMC responses to both leukaemias and lymphocytes. We suggest that E72 may express a novel HLA or non-HLA LAD.