Regulation of genes for HLA class II antigens in cell lines from patients with severe combined immunodeficiency

Extracellular Vesicles based STAT3 delivery as innovative therapeutic approach to restore STAT3 signaling deficiency

Extracellular Vesicles (EVs) have been proposed as a promising tool for drug delivery because of their natural ability to cross biological barriers, protect their cargo, and target specific cells. Moreover, EVs are not recognized by the immune system as foreign, reducing the risk of an immune response and enhancing biocompatibility. Herein, we proposed an alternative therapeutic strategy to restore STAT3 signaling exploiting STAT3 loaded EVs. This approach could be useful in the treatment of Autosomal Dominant Hyper-IgE Syndrome (AD-HIES), a rare primary immunodeficiency and multisystem disorder due to the presence of mutations in STAT3 gene. These mutations alter the signal transduction of STAT3, thereby impeding Th17 CD4+ cell differentiation that leads to the failure of immune response. We set up a simple and versatile method in which EVs were loaded with fully functional STAT3 protein. Moreover, our method allows to follow the uptake of STAT3 loaded vesicles inside cells due to the presence of EGFP in the EGFP-STAT3 fusion protein construct. Taken together, the data presented in this study could provide the scientific background for the development of new therapeutic strategy aimed to restore STAT3 signaling in STAT3 misfunction associated diseases like AD-HIES. In the future, the administration of fully functional wild type STAT3 to CD4+ T cells of AD-HIES patients might compensate its loss of function and would be beneficial for these patients, lowering the risk of infections, the use of medications, and hospitalizations.

Cell-Derived Vesicles for Antibiotic Delivery-Understanding the Challenges of a Biogenic Carrier System

Recently, extracellular vesicles (EVs) sparked substantial therapeutic interest, particularly due to their ability to mediate targeted transport between tissues and cells. Yet, EVs' technological translation as therapeutics strongly depends on better biocompatibility assessments in more complex models and elementary in vitro-in vivo correlation, and comparison of mammalian versus bacterial vesicles. With this in mind, two new types of EVs derived from human B-lymphoid cells with low immunogenicity and from non-pathogenic myxobacteria SBSr073 are introduced here. A large-scale isolation protocol to reduce plastic waste and cultivation space toward sustainable EV research is established. The biocompatibility of mammalian and bacterial EVs is comprehensively evaluated using cytokine release and endotoxin assays in vitro, and an in vivo zebrafish larvae model is applied. A complex three-dimensional human cell culture model is used to understand the spatial distribution of vesicles in epithelial and immune cells and again used zebrafish larvae to study the biodistribution in vivo. Finally, vesicles are successfully loaded with the fluoroquinolone ciprofloxacin (CPX) and showed lower toxicity in zebrafish larvae than free CPX. The loaded vesicles are then tested effectively on enteropathogenic Shigella, whose infections are currently showing increasing resistance against available antibiotics.

Enhancing the Stabilization Potential of Lyophilization for Extracellular Vesicles

Extracellular vesicles (EV) are an emerging technology as immune therapeutics and drug delivery vehicles. However, EVs are usually stored at -80 °C which limits potential clinical applicability. Freeze-drying of EVs striving for long-term stable formulations is therefore studied. The most appropriate formulation parameters are identified in freeze-thawing studies with two different EV types. After a freeze-drying feasibility study, four lyophilized EV formulations are tested for storage stability for up to 6 months. Freeze-thawing studies revealed improved colloidal EV stability in presence of sucrose or potassium phosphate buffer instead of sodium phosphate buffer or phosphate-buffered saline. Less aggregation and/or vesicle fusion occurred at neutral pH compared to slightly acidic or alkaline pH. EVs colloidal stability can be most effectively preserved by addition of low amounts of poloxamer 188. Polyvinyl pyrrolidone failed to preserve EVs upon freeze-drying. Particle size and concentration of EVs are retained over 6 months at 40 °C in lyophilizates containing 10 mm K- or Na-phosphate buffer, 0.02% poloxamer 188, and 5% sucrose. The biological activity of associated beta-glucuronidase is maintained for 1 month, but decreased after 6 months. Here optimized parameters for lyophilization of EVs that contribute to generate long-term stable EV formulations are presented.

Hot EVs - How temperature affects extracellular vesicles

In recent years, extracellular vesicles (EVs) and outer membrane vesicles (OMVs) have become an extensive and diverse field of research. They hold potential as diagnostic markers, therapeutics and for fundamental biological understanding. Despite ongoing studies, numerous information regarding function, content and stability of EVs remains unclear. If EVs and OMVs ought to be used as therapeutics and in clinical environments, their stability is one of the most important factors to be considered. Especially for formulation development, EVs and OMVs need to be stable at higher temperatures. To the best of our knowledge, very little work has been published regarding heat stability of neither EVs nor OMVs. In the present study, we investigated B lymphoblastoid cell-derived EVs and OMVs derived from myxobacterial species Sorangiineae as model vesicles. We exposed the vesicles to 37 °C, 50 °C, 70 °C and 100 °C for 1 h, 6 h and 24 h, and also autoclaved them. Interestingly, physico-chemical analyses such as size, particle concentration and protein concentration showed minor alterations, particularly at 37 °C. Flow cytometry analysis emphasised these results suggesting that after heat impact, EVs and OMVs were still able to be taken up by macrophage-like dTHP-1 cells. These data indicate that both mammalian and bacterial vesicles show intrinsic stability at physiological temperature. Our findings are important to consider for vesicle formulation and for advanced bioengineering approaches.

Residual expression of functional MHC class II molecules in twin brothers with MHC class II deficiency is cell type specific

We examined major histocompatibility complex (MHC) class II expression in B cells, peripheral blood monocytes, activated T cells, epidermal Langerhans cells, monocyte-derived dendritic cells, dermal microvascular endothelial cells (DMEC) and fibroblasts of twin brothers with MHC class II deficiency. Although residual human leucocyte antigen (HLA)-DR expression was found on a subpopulation of epidermal Langerhans cells and a subset of peripheral blood monocyte-derived dendritic cells, the patients' B cells, monocytes and activated T cells were HLA-DR negative. After treatment with interferon-gamma (IFN-gamma), the patients' DMEC expressed HLA-DR but not -DP and -DQ at the protein and mRNA level, whereas IFN-gamma failed to induce HLA-DR expression on dermal fibroblasts. The patients' monocyte-derived dendritic cells were capable of processing and presenting tetanus toxoid to autologous T cells, and patient-derived DMEC induced the proliferation of allogeneic CD4(+) T cells in an MHC class II-restricted fashion, indicating that the observed residual MHC class II surface expression was functional. The findings reported show that the defect encountered in these patients is not necessarily expressed to the same extent in different cell lineages, which is relevant for the understanding of the patients' phenotype and also illustrates that only small amounts of MHC class II are needed to mount a functional cellular immune response in vivo.

The bare lymphocyte syndrome and the regulation of MHC expression

The bare lymphocyte syndrome (BLS) is a hereditary immunodeficiency resulting from the absence of major histocompatibility complex class II (MHCII) expression. Considering the central role of MHCII molecules in the development and activation of CD4(+) T cells, it is not surprising that the immune system of the patients is severely impaired. BLS is the prototype of a "disease of gene regulation." The affected genes encode RFXANK, RFX5, RFXAP, and CIITA, four regulatory factors that are highly specific and essential for MHCII genes. The first three are subunits of RFX, a trimeric complex that binds to all MHCII promoters. CIITA is a non-DNA-binding coactivator that functions as the master control factor for MHCII expression. The study of RFX and CIITA has made major contributions to our comprehension of the molecular mechanisms controlling MHCII genes and has made this system into a textbook model for the regulation of gene expression.

Different binding of NF-Y transcriptional factor to DQA1 promoter variants

Polymorphism in the HLA-DQA1 promoter (QAP) sequences could influence the gene expression through a differential binding of transcriptional factors. Considering the main role played by the Y-box in the transcription, we focused on the QAP4 variants differing for a G vs A transition from the QAP Y-box consensus sequence. Electrophoretic Mobility Shift Assay using the two Y-box sequences was performed to determine whether this mutation could be reflected in an allele-specific binding of transcriptional factors. Indeed, the NF-Y specific band, recognised by supershift experiments, was clearly observed using the Y-box consensus probe but it was barely detectable with the QAP4 one. On the contrary, two other complexes were found to more strongly interact with QAP4 Y-box in comparison to the consensus sequence. The analysis of a selected panel of HLA homozygous lymphoblastoid cell lines by competitive RT-PCR and by Northern blotting revealed that the DQA1 *0401, *0501,*0601 alleles regulated by the QAP4 promoters were less expressed at the mRNA level than the DQA1* 0201 allele regulated by the QAP2.1 variant. In conclusion, these results show an evident reduction of NF-Y binding to the mutated QAP4 Y-box and a decreased mRNA accumulation of the DQA1 alleles regulated by these variants.

Residual MHC class II expression on mature dendritic cells and activated B cells in RFX5-deficient mice

Patients with major histocompatibility complex class II (MHC-II) deficiency are known to carry mutations in either the RFX complex or the trans-activator CIITA. While the pivotal role of CIITA for MHC-II gene transcription is supported by the essential absence of MHC-II molecules in CIITA-deficient mice, we demonstrate here that RFX5-/- mice retain expression of MHC-II in thymic medulla, mature dendritic cells, and activated B cells. Nevertheless, RFX5-/- mice develop a severe immunodeficiency due to the lack of MHC-II in thymic cortex, failure of positive selection of CD4+ T cells, and absence of MHC-II on resting B cells and resident or IFNgamma-activated macrophages. This differential requirement for CIITA and RFX5 in subsets of antigen-presenting cells may be specific for the mouse; it may, however, also exist in humans without having been noticed so far.

CCAAT-binding factor NF-Y and RFX are required for in vivo assembly of a nucleoprotein complex that spans 250 base pairs: the invariant chain promoter as a model

The events that lead to promoter accessibility within chromatin are not completely understood. The invariant chain (Ii) promoter was used as a model to determine the contribution of different DNA-binding factors in establishing occupancy of a complex promoter. Gamma interferon induction of the Ii promoter requires the cooperation of multiple cis elements including distal S, X, and Y/CCAAT elements along with proximal GC and Y/CCAAT elements. The heteromeric transcription factor NF-Y binds to both Y/CCAAT elements. Genomic footprinting was used to analyze in vivo protein-DNA contacts for integrated Ii promoters bearing mutations in each element. The results reveal a hierarchy of transcription factor loading with NF-Y binding to the distal Y/CCAAT element being required for establishing protein-DNA interactions over the entire 250 bp analyzed. Mutation of the X box disrupts binding primarily at the adjacent Y/CCAAT element along with a lesser effect on GC box binding. Importantly, this finding is verified with a cell line which lacks a functional X-box-binding factor, RFX, providing physiological validity for the strategy described here. Mutation of both the S element and the GC box results in either no or little effect on transcription factor binding. However, mutation of the proximal Y/CCAAT element disrupts binding to the adjacent GC box and partially reduces binding in the distal S/X/Y domain. The crucial role for NF-Y in establishing promoter occupancy may be related to its histone fold motif, the essential component for assembling nucleosome-like structures.

An isotype-specific activator of major histocompatibility complex (MHC) class II genes that is independent of class II transactivator

Patients with one type of major histocompatibility complex class II combined immunodeficiency have mutations in a gene termed class II transactivator (CIITA), which coordinately controls the transcription of the three major human class II genes, HLA-DR, -DQ, and -DP. However, the experimentally derived B-lymphoblastoid cell line, clone 13, expresses high levels of HLADQ in the absence of HLA-DR and HLA-DP, despite its mapping by complementation analysis to this group. It was possible that one of the clone 13 CIITA alleles bore a mutation that allowed HLA-DQ, but not HLA-DR or -DP transcription. Alternatively, another factor, distinct from CIITA, might control HLA-DQ expression. We report here that ectopic expression of CIITA cDNAs derived by reverse transcriptase polymerase chain reaction from clone 13 do not restore expression of HLA-DQ in another CIITA-deficient cell line, RJ2.2.5. In addition, no CIITA protein is detectable in clone 13 nuclear extracts. In contrast, somatic cell fusion between clone 13 and RJ2.2.5 restored expression of the HLA-DQ haplotype encoded by the RJ2.2.5 DQB gene. Taken together, these data demonstrate the existence of an HLA-DQ isotype-specific trans-acting factor, which functions independently of CIITA.

Major histocompatibility complex class II deficiency: a clinical review

Major histocompatibility complex Class II deficiency or bare lymphocyte syndrome is a rare combined immunodeficiency that accounts for 5% of all cases of severe combined immunodeficiency. The syndrome is characterized by a lack of human leucocyte antigen Class II gene expression, absence of cellular and humoral T-cell immune response to foreign antigens, and impaired antibody productions, resulting in extreme susceptibility to viral, bacterial and fungal infections. In some patients, there is a reduced cell surface expression of human leucocyte antigen Class I molecules also. Major histocompatibility complex Class II deficiency is an autosomal recessive disease, most frequent in the Mediterranean area. The disease is caused by impaired gene regulation involving trans-acting proteins. Somatic cell genetics using cell fusion experiments identified four complementation groups, all resulting in the same clinical manifestation. Two regulatory genes have been identified so far: Class II trans activator and regulatory factor X5. Supportive treatment includes intravenous gammaglobulin and prophylaxis against Pneumocystis carinii. The only curative treatment is bone-marrow transplantation.

Regulation of MHC class II genes: lessons from a disease

Precise regulation of major histocompatibility complex class II (MHC-II) gene expression plays a crucial role in the control of the immune response. A major breakthrough in the elucidation of the molecular mechanisms involved in MHC-II regulation has recently come from the study of patients that suffer from a primary immunodeficiency resulting from regulatory defects in MHC-II expression. A genetic complementation cloning approach has led to the isolation of CIITA and RFX5, two essential MHC-II gene transactivators. CIITA and RFX5 are mutated in these patients, and the wild-type genes are capable of correcting their defect in MHC-II expression. The identification of these regulatory factors has furthered our understanding of the molecular mechanisms that regulate MHC-II genes. CIITA was found to be a non-DNA binding transactivator that functions as a molecular switch controlling both constitutive and inducible MHC-II expression. The finding that RFX5 is a subunit of the nuclear RFX-complex has confirmed that a deficiency in the binding of this complex is indeed the molecular basis for MHC-II deficiency in the majority of patients. Furthermore, the study of RFX has demonstrated that MHC-II promoter activity is dependent on the binding of higher-order complexes that are formed by highly specific cooperative binding interactions between certain MHC-II promoter-binding proteins. Two of these proteins belong to families of which the other members, although capable of binding to the same DNA motifs, are probably not directly involved in the control of MHC-II expression. Finally, the facts that CIITA and RFX5 are both essential and highly specific for MHC-II genes make possible novel strategies designed to achieve immunomodulation via transcriptional intervention.

Genetic evidence for a new type of major histocompatibility complex class II combined immunodeficiency characterized by a dyscoordinate regulation of HLA-D alpha and beta chains

Major histocompatibility complex (MHC) class II combined immunodeficiency (CID), also known as type II bare lymphocyte syndrome, is an autosomal recessive genetic disorder characterized by the complete lack of expression of MHC class II antigens. The defect results from a coordinated lack of transcription of all class II genes. Cell fusion studies using many patient- and experimentally derived class II-negative cell lines have identified four distinct genetic complementation groups. In this report, we present genetic evidence that cell lines derived from two newly described MHC class II-deficient patients, KER and KEN, represent a fifth complementation group. In addition, the KER and KEN cell lines display a unique pattern of dyscoordinate regulation of their MHC class II genes, which is reflected in a new phenotype of in vivo promoter occupancy as revealed by in vivo genomic footprinting. These data point to a new defect that can result in the MHC class II-deficient phenotype.

Human MHC class II gene transcription directed by the carboxyl terminus of CIITA, one of the defective genes in type II MHC combined immune deficiency

Type II major histocompatibility complex combined immune deficiency (type II MHC CID or bare lymphocyte syndrome) is a congenital immunodeficiency disease characterized by absent MHC class II expression. Four distinct complementation groups have been identified. Recently, the defective gene in group II type II MHC CID has been isolated and termed CIITA. Here, we demonstrate that CIITA is an MHC class II gene-specific transcription activator. The transcription activation function is provided by the N-terminal acidic domain (amino acids 26-137), which is experimentally exchangeable with a heterologous viral transcription-activating domain. The specificity of CIITA for three major MHC class II genes, DR, DQ and DP, is mediated by its remaining C-terminal residues (amino acids 317-1130). The transactivation of multiple cis elements, especially S and X2, of the DR alpha proximal promoter in group II CID cells is CIITA dependent. Since CIITA overexpression in normal cells did not increase class II expression, we propose that initiation of CIITA expression serves as the on-off switch, while availability of downstream interactor(s) limits transcription.

A novel DNA-binding regulatory factor is mutated in primary MHC class II deficiency (bare lymphocyte syndrome)

Regulation of MHC class II gene expression is an essential aspect of the control of the immune response. Primary MHC class II deficiency is a genetically heterogeneous disease of gene regulation that offers the unique opportunity of a genetic approach for the identification of the functionally relevant regulatory genes and factors. Most patients exhibit a characteristic defect in the binding of a nuclear complex, RFX, to the X box motif of MHC class II promoters. Genetic complementation of a B-lymphocyte cell line from such a patient with a cDNA expression library has allowed us to isolate RFX5, the regulatory gene responsible for the MHC class II deficiency. This gene encodes a novel DNA-binding protein that is indeed a subunit of the RFX complex. Mutations in the RFX5 gene have been characterized in two patients. Transfection of the patient's cells with the RFX5 cDNA repairs the binding defect and fully restores expression of all the endogenous MHC class II genes in vivo.

Molecular characterization of major histocompatibility complex class II gene expression and demonstration of antigen-specific T cell response indicate a new phenotype in class II-deficient patients

Major histocompatibility complex (MHC) class II deficiency is an inherited autosomal recessive combined immunodeficiency. The disease is known as bare lymphocyte syndrome (BLS). BLS is characterized by a lack of constitutive MHC class II expression on macrophages and B cells as well as a lack of induced MHC class II expression on cells other than professional antigen-presenting cells (APCs) due to the absence of mRNA and protein of the human leukocyte antigen (HLA) class II molecules, designated HLA-DR, -DQ, and -DP. The defect in gene expression is located at the transcriptional level and affects all class II genes simultaneously. Here we have analyzed transcription and protein expression of class II antigens in Epstein-Barr virus (EBV)-transformed B lymphoblastoid cell lines and mononuclear cells (MNCs) of twin brothers. Whereas flow cytometric analysis failed to detect class II antigens on the cell surface of the patients' EBV-B cells and MNCs, examination of the genes coding for HLA-DR, -DQ, -DP, and the invariant chain (Ii) by reverse transcriptase-polymerase chain reaction amplification resulted in an unusual mRNA pattern in the B cell lines of the patients (HLA-DR alpha +, -DR beta, -DQ alpha +, -DQ beta -, -DP alpha -; -DP beta +, Ii+). In accordance with these findings no HLA-DR beta-specific protein was detected by immunoblotting, whereas low levels of HLA-DR alpha and normal levels of Ii were present. In contrast to EBV-B cells, the MNCs of both patients displayed a residual HLA-DR beta, -DQ beta, and -DP alpha mRNA signal. Furthermore, HLA-DR beta-specific protein was found in addition to HLA-DR alpha by immunoblotting of cell lysates, even though it was clearly decreased as compared with controls. Our results indicate that the defect in class II antigen expression is not necessarily present to the same extent in B cells and cells of other lineages. mRNA levels of HLA-DR beta were found to be enriched in adherent cells within the MNC fraction. Further investigations indicated that the MHC class II expressed is functional in antigen presentation, as the two boys' CD4+ T cells became activated and expressed interleukin-2R after stimulation of peripheral blood mononuclear cell cultures with recall antigen (tetanus toxoid). Furthermore, T cells tested in one of the two patients responded to both MHC class I and II allostimulation, and this response was inhibited by monoclonal antibodies of the respective specificity.(ABSTRACT TRUNCATED AT 400 WORDS)

Signal transmission through MHC class II molecules in a human B lymphoid progenitor cell line: different signaling pathways depending on the maturational stages of B cells

The function of MHC class II HLA-DR molecules expressed on a human B lymphoid progenitor cell line FL8.2.4.4 (abbreviated as FL4.4) was examined. FL4.4 cells expressed HLA-DR molecules and stimulation of the DR molecules by anti-DR mAb or by superantigen TSST-1 induced strong augmentation of homocytic aggregation and protein tyrosine phosphorylation in FL4.4 cells. Induced homocytic aggregation in FL4.4 consists both of LFA-1/ICAM-1-dependent and -independent pathways as revealed by mAb blocking experiments. Metabolic inhibitors, NaN3 and cytochalasin B, blocked the induced homocytic aggregation of FL4.4. Early mature Daudi B cell lines also showed a similar type of homocytic aggregation by stimulation with anti-DR mAb. Daudi cells are more sensitive to protein kinase inhibitors herbimycin A and H7 than FL4.4 cells in their blocking of induced homocytic aggregation, while W7 showed stronger inhibitory effects on FL4.4 cells than on Daudi cells. Western blotting analysis revealed that the stimulation of DR molecules induced protein tyrosine phosphorylation of 100-kDa, 90-kDa, 60-kDa and 55-kDa proteins in FL4.4 cells, while, in Daudi cells 110-kDa, 100-kDa and 80-kDa proteins were phosphorylated. These results suggest that different signaling pathways through class II molecules are employed depending on the maturational stage of B-cell differentiation.

Functional complementation of major histocompatibility complex class II regulatory mutants by the purified X-box-binding protein RFX

Major histocompatibility complex (MHC) class II deficiency, or bare lymphocyte syndrome (BLS), is a disease of gene regulation. Patients with BLS have been classified into at least three complementation groups (A, B, and C) believed to correspond to three distinct MHC class II regulatory genes. The elucidation of the molecular basis for this disease will thus clarify the mechanisms controlling the complex regulation of MHC class II genes. Complementation groups B and C are characterized by a lack of binding of RFX, a nuclear protein that normally binds specifically to the X box cis-acting element present in the promoters of all MHC class II genes. We have now purified RFX to near homogeneity by affinity chromatography. Using an in vitro transcription system based on the HLA-DRA promoter, we show here that extracts from RFX-deficient cells from patients with BLS (BLS cells) in groups B and C, which are transcriptionally inactive in this assay, can be complemented to full transcriptional activity by the purified RFX. As expected, purified RFX also restores a completely normal pattern of X box-binding complexes in these mutant extracts. This provides the first direct functional evidence that RFX is an activator of MHC class II gene transcription and that its absence is indeed responsible for the regulatory defect in MHC class II gene expression in patients with BLS.

Functional complementation of major histocompatibility complex class II regulatory mutants by the purified X-box-binding protein RFX

Major histocompatibility complex (MHC) class II deficiency, or bare lymphocyte syndrome (BLS), is a disease of gene regulation. Patients with BLS have been classified into at least three complementation groups (A, B, and C) believed to correspond to three distinct MHC class II regulatory genes. The elucidation of the molecular basis for this disease will thus clarify the mechanisms controlling the complex regulation of MHC class II genes. Complementation groups B and C are characterized by a lack of binding of RFX, a nuclear protein that normally binds specifically to the X box cis-acting element present in the promoters of all MHC class II genes. We have now purified RFX to near homogeneity by affinity chromatography. Using an in vitro transcription system based on the HLA-DRA promoter, we show here that extracts from RFX-deficient cells from patients with BLS (BLS cells) in groups B and C, which are transcriptionally inactive in this assay, can be complemented to full transcriptional activity by the purified RFX. As expected, purified RFX also restores a completely normal pattern of X box-binding complexes in these mutant extracts. This provides the first direct functional evidence that RFX is an activator of MHC class II gene transcription and that its absence is indeed responsible for the regulatory defect in MHC class II gene expression in patients with BLS.

T cell differentiation and generation of the antigen-specific T cell repertoire in man: observations in MHC class II deficiency

The circulating T cell pool of an MHC class II-deficient patient was shown to lack the MHC class II-specific T cell functions. This was demonstrated by the absence of MHC class II-specific alloreactive T cells and a substantially decreased number of circulating CD4+ lymphocytes. The patient's T cells did respond to an allostimulus, although the restriction pattern of this reaction remains speculative. The function and distribution of peripheral T cell subsets from the patient resemble findings in MHC class II-deficient mice, which also lack interaction of T cell precursors with MHC class II-bearing accessory cells during thymic differentiation. Our data support the concept that T cell differentiation in humans is similar, and that the human MHC-restricted T cell repertoire depends on prior interaction of T cell precursors with self MHC.

Major histocompatibility complex class II deficiency: clinical manifestations, immunologic features, and outcome

Major histocompatibility complex class II deficiency (bare lymphocyte syndrome) is a rare primary immunodeficiency disorder characterized by profound defects in human leukocyte antigen class II expression, inconsistent and incomplete expression of human leukocyte antigen class I molecules, and a complete lack of cellular and humoral immune responses to foreign antigens. To define the clinical and immunologic characteristics, outcome, and natural history of major histocompatibility complex class II deficiency, we retrospectively analyzed 30 consecutive patients. Clinical onset occurred in the first year of life, usually involving recurrent bronchopulmonary infections and chronic diarrhea. The clinical course was complicated by viral meningoencephalitis, hepatitis, cholangitis, and various autoimmune phenomena. Prognosis was very poor: the mean age at the time of death was 4 years. The main cause of death was overwhelming viral infection. Recent advances in bone marrow transplantation have raised hopes of curative treatment: 6 of 14 patients who underwent bone marrow transplantation were cured. Long-term survival after human leukocyte antigen-identical and haploidentical bone marrow transplantation seemed to depend primarily on the presence of preexisting viral infections.

The human leukocyte antigens and their relationship to infection

Human leukocyte antigen DR (HLA-DR) expression on peripheral blood monocytes has been found to correlate highly with infection in many clinical scenarios. This is particularly true for the trauma patient, where changes in HLA-DR expression predate and therefore often predict development of infection. Expression of this antigen is limited to immunocompetent cells, such as B lymphocytes, macrophages, and activated T cells. The HLA-DR heterodimer is required for major histocompatibility complex restricted antigen presentation, a key step in the development of a specific immune response. The degree of monocyte HLA-DR expression may reflect the ability eventually to present antigen, since close correlation has been found between the two. There was remarkable reproducibility of monocyte HLA-DR expression among > 100 asymptomatic volunteers without regard to age, gender, race, and sampling time. Immunosuppressive medication had no effect. Incubation of monocytes from severely infected patients with endotoxin distinguished survivors from those who died by enhanced HLA-DR expression in the survivors. Of several agents that enhance HLA-DR expression, interferon-gamma has received the most attention in experimental models as well as humans. Although promising in selected patients, further clinical trials will be needed to define its specific role. Identification of the patient at high risk for infection, particularly following trauma, will be crucial for the efficient evaluation of future therapeutic interventions. Monocyte HLA-DR expression is the first simple assessment of the host immune response to play an important role in this endeavor.

The genes for MHC class II regulatory factors RFX1 and RFX2 are located on the short arm of chromosome 19

RFX1 is a transacting DNA-binding regulatory factor involved in the control of MHC class II gene expression. RFX2 is a structurally very similar protein with identical DNA binding features. A member of the family of RFX factors is affected in an autosomal recessive disease, MHC class II deficient combined immunodeficiency (CID), caused by a defect in a trans-acting regulatory factor controlling MHC class II gene expression. In situ hybridization with 3H-labeled RFX1 cDNA has allowed us to identify two distinct targets on the short arm of chromosome 19 (19p13.1 and 19p13.2-p13.3). With the use of biotinylated genomic cosmid clones specific for RFX1 and RFX2, respectively, it was then possible to localize RFX1 at 19p13.1 and RFX2 at 19p13.2-p13.3. These two regulatory genes are thus assigned to a region of high gene density and RFX1 is close to another DNA-binding factor, LYL1.

Effect of epidermal growth factor in HLA class I and class II transcription and protein expression in human breast adenocarcinoma cell lines

The spontaneous expression of HLA class I and class II molecules in two human breast carcinoma cell lines (MCF7, T47D) and their modulation during epidermal growth factor treatment are reported. Transcription was analysed by Northern blot and hybridisation with HLA class II and class I cDNA specific probes. The expression of cell surface determinants was examined by internal protein labelling with 35s-methionine, immunoprecipitation with monoclonal antibodies specific for HLA class I or class II, followed by isolation of the immune complex on protein A-Sepharose; at least a quantification of glycoprotein was performed by chromatofocusing. Glycoprotein quantification showed a significant increase of HLA class I and class II (DR) antigen expression after stimulation by epidermal growth factor (0.02 microgram ml-1) in the two cell lines, when compared with untreated cell controls. However, with epidermal growth factor treatment of MCF7 and T47D cells, low increases in the amounts of HLA class I and class II RNA were obtained. These differences between expressed antigens and correspondent RNA amounts would be explained by the fact that EGF in these two cell lines acts more in post-transcription for HLA class I and class II antigens.

B-cell factor 1 is required for optimal expression of the DRA promoter in B cells

The X box in the DRA promoter of the human histocompatibility complex is required for expression of the DRA gene in B cells. We show that a B-cell factor binds to a sequence that is clearly distinguishable from binding sites for the previously described X box binding nuclear proteins RF-X, NF-X, NF-Xc, NF-S, hXBP, and AP-1. Mutations in the DRA X box that disrupt the binding of this factor result in a lower level of gene expression, as does the presence of Id (a trans-dominant regulatory protein that negatively regulates helix-loop-helix proteins). Furthermore, this factor is recognized by antibodies directed against the helix-loop-helix protein A1, a mouse homolog of the immunoglobulin enhancer binding proteins E12/E47, and it binds to sequences in other genes that were previously shown to bind these proteins. By these criteria, this factor is BCF-1.

B-cell factor 1 is required for optimal expression of the DRA promoter in B cells

The X box in the DRA promoter of the human histocompatibility complex is required for expression of the DRA gene in B cells. We show that a B-cell factor binds to a sequence that is clearly distinguishable from binding sites for the previously described X box binding nuclear proteins RF-X, NF-X, NF-Xc, NF-S, hXBP, and AP-1. Mutations in the DRA X box that disrupt the binding of this factor result in a lower level of gene expression, as does the presence of Id (a trans-dominant regulatory protein that negatively regulates helix-loop-helix proteins). Furthermore, this factor is recognized by antibodies directed against the helix-loop-helix protein A1, a mouse homolog of the immunoglobulin enhancer binding proteins E12/E47, and it binds to sequences in other genes that were previously shown to bind these proteins. By these criteria, this factor is BCF-1.

Transcriptional regulation of HLA-DRA gene

Transcriptional regulation of class II genes is complex. DRA, for example, is expressed in both tissue-specific and lymphokine-inducible fashion. High levels of expression in B and activated T cells depend upon a lymphoid-specific transcriptional enhancer located in the first intron and on the upstream and downstream promoter elements. Conserved upstream promoter Z and X sequences (CUS) are the main determinants of this complex regulation. At least four distinct trans-acting factors that might be differentially expressed in various cell types bind to these Z and X boxes. These are members of JUN, helix-loop-helix (HLH), C/EBP and ETS families of proteins.

HLA-DR antigen expression on peripheral blood monocytes correlates with surgical infection

Monocyte human leukocyte antigen-DR (HLA-DR) expression has correlated closely with clinical outcome in severely injured patients at high risk for infection. Monocytes from 77 asymptomatic volunteers expressed HLA-DR antigen with minimal variability in respect to age, gender, race, time of day or year, or serum alcohol level. Patients who developed infection after elective laparotomy had a significantly lower mean percentage of monocytes expressing HLA-DR antigen and a lower mean fluorescent intensity than uninfected patients (p less than 0.05). Severely infected nonsurgical patients had significantly lower values than normal volunteers (p less than 0.01), and the mean fluorescent intensity of those who died from infection was significantly lower than that of those who survived (p less than 0.05). Patients on immunosuppressive regimens after renal transplantation had levels of HLA-DR expression similar to those of the volunteers. Monocyte HLA-DR expression was found to be a reliable marker of clinical infection and showed remarkable reproducibility within the normal uninfected study population.

Class II-antigen-negative patient and mutant B-cell lines represent at least three, and probably four, distinct genetic defects defined by complementation analysis

Expression of class II major histocompatibility complex antigens in defective B-lymphoblastoid cell lines from patients with class II antigen deficiency and from in vitro mutants generated with the same phenotype was studied. By heterogenetic fusion experiments, at least three, and probably four, complementation groups were defined. Furthermore, clone 13 (a DR-, DP-, but DQ+ cell line) appeared to belong to the RJ2.2.5 complementation group, for which all other members are DR-, DP-, and also DQ-. Thus, it is hypothesized that the cell lines of this group lack the activity of a gene that can differentially regulate the DR/DP and the DQ promoters.

Transcription of a subset of human class II major histocompatibility complex genes is regulated by a nucleoprotein complex that contains c-fos or an antigenically related protein

Transcriptional regulation of the human major histocompatibility complex class II genes requires at least two upstream elements, the X and Y boxes, located in the -50- to -150-base-pair region of all class II promoters. The DRA and DPB promoters contain phorbol ester-responsive elements overlapping the 3' side of their X boxes. Mutation of this sequence down-regulates the efficiency of the DRA promoter, suggesting that a positive regulator(s) binds to this site. In this report, anti-sense c-fos RNA and an anti-c-fos antibody were used to show that the product of the protooncogene c-fos or an antigenically related protein is a component of a complex that binds to the X box and is required for maximal transcription from the DRA and DPB promoters. As c-fos (or its related proteins) cannot bind alone to DNA, these results suggest that it may dimerize with other members of the JUN/AP-1 family, such as hXBP1, to participate in the activation of a subset of class II major histocompatibility complex genes.

An isotype-specific trans-acting factor is defective in a mutant B cell line that expresses HLA-DQ, but not -DR or -DP

The B lymphoblastoid cell line clone 13 (a subclone of the mutant cell line P3JHR-1) has been found to express high levels of HLA-DQ; by contrast, HLA-DR and -DP antigens are not expressed and cannot be induced by interferon gamma. Northern blot analysis using gene-specific probes indicated that the lack of surface expression of the DR and DP antigens is due to a marked decrease in the levels of steady-state RNA for both the alpha and beta chains. Southern blots demonstrated that none of the transcriptionally repressed genes are grossly deleted. Preparations of interspecific transient heterokaryons between clone 13 and the class II antigen-positive murine B cell lymphoma, A20, resulted in reactivation of the DRA gene and surface expression of both the DR and DP molecules. The efficiency of the DRA promoter relative to the DQB promoter is markedly and specifically diminished in clone 13 (P3JHR-1) as compared with the parental cell line, Jijoye, as assayed both by transient expression of appropriate chloramphenicol acetyltransferase gene (CAT) constructs and by in vitro transcription analysis. These data clearly demonstrate the existence of an isotype-specific trans-acting factor, and provide direct evidence that the highly homologous class II genes have distinct regulatory mechanisms.

MHC class II regulatory factor RFX has a novel DNA-binding domain and a functionally independent dimerization domain

The regulation of MHC class II gene expression controls T-cell activation and, hence, the immune response. Among the nuclear factors observed to bind to conserved DNA sequences in human leukocyte antigen (HLA) class II gene promoters, RFX is of special interest: Its binding is defective in congenital HLA class II deficiency, a disease of class II gene regulation. The cloning of an RFX cDNA has allowed us to show by transfection of a plasmid directing the synthesis of antisense RFX RNA that RFX is a class II gene regulatory factor. RFX is a novel 979-amino-acid DNA-binding protein that contains three structurally and functionally separate domains. The 91-amino-acid DNA-binding domain is distinct from other known DNA-binding motifs but may be distantly related to the helix-loop-helix motif. The most striking property of RFX is that it can bind stably to the class II X box as either a monomer or a homodimer and that the domain responsible for dimerization is distant from and functionally independent of the DNA-binding domain. This distinguishes RFX from other known dimeric DNA-binding proteins. It also implies that an RFX homodimer has two potential DNA-binding sites. We therefore speculate that RFX could form a DNA loop by cross-linking the two X-box sequences found far apart upstream of MHC class II genes.

Transcription analysis of class II human leukocyte antigen genes from normal and immunodeficient B lymphocytes, using polymerase chain reaction

The RNA transcript levels of all human leukocyte antigen class II loci were determined from class II congenital immunodeficient B cells by polymerase chain reaction amplification of cDNA. No mRNA was observed under conditions in which 0.01% normal levels could be visualized. Pre-mRNA could be amplified from normal B cells but not from immunodeficient B cells, indicating a transcription defect.

Transcription analysis of class II human leukocyte antigen genes from normal and immunodeficient B lymphocytes, using polymerase chain reaction

The RNA transcript levels of all human leukocyte antigen class II loci were determined from class II congenital immunodeficient B cells by polymerase chain reaction amplification of cDNA. No mRNA was observed under conditions in which 0.01% normal levels could be visualized. Pre-mRNA could be amplified from normal B cells but not from immunodeficient B cells, indicating a transcription defect.

The class II major histocompatibility complex antigen deficiency syndrome: consequences of absent class II major histocompatibility antigens for lymphocyte differentiation and function

The class II major histocompatibility complex antigen deficiency syndrome is a rare immunodeficiency disease associated with defective expression of the class II antigens encoded for by the major histocompatibility complex. Clinically, this syndrome is manifest as a combined immunodeficiency presenting early in life, and affected individuals are susceptible to a variety of severe and/or opportunistic infections. Chronic, severe diarrhea and malabsorption are also characteristically found, and death is common within the first few years of life. Although the precise molecular lesions responsible for the failure of membrane antigen expression in this syndrome have not yet been identified, the pathogenetic mechanisms involve regulatory defects in the transcription of structural genes encoding for class II antigens. The absence of class II MHC antigens results in profound abnormalities in lymphocyte function and differentiation. Of central importance is the defective MHC-restricted interactions between CD4+ "helper" T lymphocytes and the various types of antigen-presenting cells found in the skin and elsewhere. The absence of class II MHC antigens also appears to alter the ability of affected B cells to be activated by a variety of membrane-mediated stimuli, and it profoundly disrupts both the intrathymic development and post-thymic differentiation of immunoregulatory T cells. This "experiment of nature" thus demonstrates the critical role of class II MHC antigens in the proper development and function of the immune system.

Two DNA-binding proteins discriminate between the promoters of different members of the major histocompatibility complex class II multigene family

The regulation of major histocompatibility complex (MHC) class II gene expression is a key feature of the control of normal and abnormal immune responses. In humans, class II alpha - and beta-chain genes are organized in a multigene family with three distinct subregions, HLA-DR, -DQ, and -DP. The regulation of these genes is generally coordinated, and their promoters contain highly conserved motifs, in particular the X and Y boxes. We have identified five distinct proteins that bind to specific DNA sequences within the first 145 base pairs of the HLA-DR promoter, a segment known to be functionally essential for class II gene regulation. Among these, RF-X is of special interest, since mutants affected in the regulation of MHC class II gene expression have a specific defect in RF-X binding. Unexpectedly, RF-X displays a characteristic gradient of binding affinities for the X boxes of three alpha-chain genes (DRA greater than DPA much greater than DQA). The same observation was made with recombinant RF-X. We also describe a novel factor, NF-S, which bound to the spacer region between the X and Y boxes of class II promoters. NF-S exhibited a reverse gradient of affinity compared with RF-X (DQA greater than DPA much greater than DRA). As expected, RF-X bound well to the mouse IE alpha promoter, while NF-S bound well to IA alpha. The drastic differences in the binding of RF-X and NF-S to different MHC class II promoters contrasts with the coordinate regulation of HLA-DR, -DQ, and -DP genes.

Two DNA-binding proteins discriminate between the promoters of different members of the major histocompatibility complex class II multigene family

The regulation of major histocompatibility complex (MHC) class II gene expression is a key feature of the control of normal and abnormal immune responses. In humans, class II alpha - and beta-chain genes are organized in a multigene family with three distinct subregions, HLA-DR, -DQ, and -DP. The regulation of these genes is generally coordinated, and their promoters contain highly conserved motifs, in particular the X and Y boxes. We have identified five distinct proteins that bind to specific DNA sequences within the first 145 base pairs of the HLA-DR promoter, a segment known to be functionally essential for class II gene regulation. Among these, RF-X is of special interest, since mutants affected in the regulation of MHC class II gene expression have a specific defect in RF-X binding. Unexpectedly, RF-X displays a characteristic gradient of binding affinities for the X boxes of three alpha-chain genes (DRA greater than DPA much greater than DQA). The same observation was made with recombinant RF-X. We also describe a novel factor, NF-S, which bound to the spacer region between the X and Y boxes of class II promoters. NF-S exhibited a reverse gradient of affinity compared with RF-X (DQA greater than DPA much greater than DRA). As expected, RF-X bound well to the mouse IE alpha promoter, while NF-S bound well to IA alpha. The drastic differences in the binding of RF-X and NF-S to different MHC class II promoters contrasts with the coordinate regulation of HLA-DR, -DQ, and -DP genes.

Mutational analysis of the DRA promoter: cis-acting sequences and trans-acting factors

Class II major histocompatibility genes are expressed at high levels in B lymphocytes and are gamma interferon (IFN-gamma) inducible in many other cells. Previously, we observed that DRA promoter sequences from positions -150 to +31 determine the tissue specificity of this class II gene. Moreover, Z and X boxes located between positions -145 and -87 conferred B-cell specificity and IFN-gamma inducibility upon a heterologous promoter. In this study, sequences from positions -145 to -35 in the DRA promoter were systematically mutated by using oligonucleotide cassettes. Z (-131 to -125), pyrimidine (-116 to -109), X (-108 to -95), Y (-73 to -61), and octamer (-52 to -45) boxes were required for B-cell specificity and, with the exception of the octamer box, for IFN-gamma inducibility. Z box and sequences flanking Z and X boxes helped to determine low levels of expression in T and uninduced cells. In phenotypically distinct cells, shared and distinct proteins bound to these conserved upstream sequences. However, few correlations between expression and DNA-binding proteins could be made. Similar proteins bound to Z and X boxes, and the Z box most likely represents a duplication of the X box.