HLA-DR polymorphism affects the interaction with CD4

New insight into the role of fibroblasts in the epithelial immune microenvironment in the single-cell era

The skin is exposed to environmental challenges and contains heterogeneous cell populations such as epithelial cells, stromal cells, and skin-resident immune cells. As the most abundant type of stromal cells, fibroblasts have been historically considered silent observers in the immune responses of the cutaneous epithelial immune microenvironment (EIME), with little research conducted on their heterogeneity and immune-related functions. Single-cell RNA sequencing (scRNA-seq) and spatial transcriptomics (ST) have overcome the limitations of bulk RNA sequencing and help recognize the functional and spatial heterogeneity of fibroblasts, as well as their crosstalk with other types of cells in the cutaneous EIME. Recently, emerging single-cell sequencing data have demonstrated that fibroblasts notably participate in the immune responses of the EIME and impact the initiation and progression of inflammatory skin diseases. Here, we summarize the latest advances in the role of fibroblasts in the cutaneous EIME of inflammatory skin diseases and discuss the distinct functions and molecular mechanisms of activated fibroblasts in fibrotic skin diseases and non-fibrotic inflammatory skin diseases. This review help unveil the multiple roles of fibroblasts in the cutaneous EIME and offer new promising therapeutic strategies for the management of inflammatory skin diseases by targeting fibroblasts or the fibroblast-centered EIME.

Fucosylation of HLA-DRB1 regulates CD4+ T cell-mediated anti-melanoma immunity and enhances immunotherapy efficacy

Immunotherapy efficacy is limited in melanoma, and combinations of immunotherapies with other modalities have yielded limited improvements but also adverse events requiring cessation of treatment. In addition to ineffective patient stratification, efficacy is impaired by paucity of intratumoral immune cells (itICs); thus, effective strategies to safely increase itICs are needed. We report that dietary administration of L-fucose induces fucosylation and cell surface enrichment of the major histocompatibility complex (MHC)-II protein HLA-DRB1 in melanoma cells, triggering CD4+ T cell-mediated increases in itICs and anti-tumor immunity, enhancing immune checkpoint blockade responses. Melanoma fucosylation and fucosylated HLA-DRB1 associate with intratumoral T cell abundance and anti-programmed cell death protein 1 (PD1) responder status in patient melanoma specimens, suggesting the potential use of melanoma fucosylation as a strategy for stratifying patients for immunotherapies. Our findings demonstrate that fucosylation is a key mediator of anti-tumor immunity and, importantly, suggest that L-fucose is a powerful agent for safely increasing itICs and immunotherapy efficacy in melanoma.

Single-Cell Transcriptional Analysis Deciphers the Inflammatory Response of Skin-Resident Stromal Cells

The skin is the outermost barrier of the body. It has developed a sophisticated system against the ever-changing environment. The application of single-cell technologies has revolutionized dermatology research and unraveled the changes and interactions across skin resident cells in the healthy and inflamed skin. Single-cell technologies have revealed the critical roles of stromal cells in an inflammatory response and explained a series of plausible previous findings concerning skin immunity. Here, we summarized the functional diversity of skin stromal cells defined by single-cell analyses and how these cells orchestrated events leading to inflammatory diseases, including atopic dermatitis, psoriasis, vitiligo, and systemic lupus erythematosus.

Single cell transcriptional zonation of human psoriasis skin identifies an alternative immunoregulatory axis conducted by skin resident cells

Psoriasis is the most common skin disease in adults. Current experimental and clinical evidences suggested the infiltrating immune cells could target local skin cells and thus induce psoriatic phenotype. However, recent studies indicated the existence of a potential feedback signaling loop from local resident skin cells to infiltrating immune cells. Here, we deconstructed the full-thickness human skins of both healthy donors and patients with psoriasis vulgaris at single cell transcriptional level, and further built a neural-network classifier to evaluate the evolutional conservation of skin cell types between mouse and human. Last, we systematically evaluated the intrinsic and intercellular molecular alterations of each cell type between healthy and psoriatic skin. Cross-checking with psoriasis susceptibility gene loci, cell-type based differential expression, and ligand-receptor communication revealed that the resident psoriatic skin cells including mesenchymal and epidermis cell types, which specifically harbored the target genes of psoriasis susceptibility loci, intensively evoked the expression of major histocompatibility complex (MHC) genes, upregulated interferon (INF), tumor necrosis factor (TNF) signalling and increased cytokine gene expression for primarily aiming the neighboring dendritic cells in psoriasis. The comprehensive exploration and pathological observation of psoriasis patient biopsies proposed an uncovered immunoregulatory axis from skin local resident cells to immune cells, thus provided a novel insight for psoriasis treatment. In addition, we published a user-friendly website to exhibit the transcriptional change of each cell type between healthy and psoriatic human skin.

Next-Generation HLA Sequence Analysis Uncovers Seven HLA-DQ Amino Acid Residues and Six Motifs Resistant to Childhood Type 1 Diabetes

HLA-DQA1 and -DQB1 genes have significant and potentially causal associations with autoimmune type 1 diabetes (T1D). To follow up on the earlier analysis on high-risk HLA-DQ2.5 and DQ8.1, the current analysis uncovers seven residues (αa1, α157, α196, β9, β30, β57, and β70) that are resistant to T1D among subjects with DQ4-, 5-, 6-, and 7-resistant DQ haplotypes. These 7 residues form 13 common motifs: 6 motifs are significantly resistant, 6 motifs have modest or no associations (P values >0.05), and 1 motif has 7 copies observed among control subjects only. The motifs "DAAFYDG," "DAAYHDG," and "DAAYYDR" have significant resistance to T1D (odds ratios [ORs] 0.03, 0.25, and 0.18; P = 6.11 × 10^-24, 3.54 × 10^-15, and 1.03 × 10^-21, respectively). Remarkably, a change of a single residue from the motif "DAAYHDG" to "DAAYHSG" (D to S at β57) alters the resistance potential, from resistant motif (OR 0.15; P = 3.54 × 10^-15) to a neutral motif (P = 0.183), the change of which was significant (Fisher P value = 0.0065). The extended set of linked residues associated with T1D resistance and unique to each cluster of HLA-DQ haplotypes represents facets of all known features and functions of these molecules: antigenic peptide binding, peptide-MHC class II complex stability, β167-169 RGD loop, T-cell receptor binding, formation of homodimer of α-β heterodimers, and cholesterol binding in the cell membrane rafts. Identification of these residues is a novel understanding of resistant DQ associations with T1D. Our analyses endow potential molecular approaches to identify immunological mechanisms that control disease susceptibility or resistance to provide novel targets for immunotherapeutic strategies.

Eleven Amino Acids of HLA-DRB1 and Fifteen Amino Acids of HLA-DRB3, 4, and 5 Include Potentially Causal Residues Responsible for the Risk of Childhood Type 1 Diabetes

Next-generation targeted sequencing of HLA-DRB1 and HLA-DRB3, -DRB4, and -DRB5 (abbreviated as DRB345) provides high resolution of functional variant positions to investigate their associations with type 1 diabetes risk and with autoantibodies against insulin (IAA), GAD65 (GADA), IA-2 (IA-2A), and ZnT8 (ZnT8A). To overcome exceptional DR sequence complexity as a result of high polymorphisms and extended linkage disequilibrium among the DR loci, we applied a novel recursive organizer (ROR) to discover disease-associated amino acid residues. ROR distills disease-associated DR sequences and identifies 11 residues of DRB1, sequences of which retain all significant associations observed by DR genes. Furthermore, all 11 residues locate under/adjoining the peptide-binding groove of DRB1, suggesting a plausible functional mechanism through peptide binding. The 15 residues of DRB345, located respectively in the β49-55 homodimerization patch and on the face of the molecule shown to interact with and bind to the accessory molecule CD4, retain their significant disease associations. Further ROR analysis of DR associations with autoantibodies finds that DRB1 residues significantly associated with ZnT8A and DRB345 residues with GADA. The strongest association is between four residues (β14, β25, β71, and β73) and IA-2A, in which the sequence ERKA confers a risk association (odds ratio 2.15, P = 10^-18), and another sequence, ERKG, confers a protective association (odds ratio 0.59, P = 10^-11), despite a difference of only one amino acid. Because motifs of identified residues capture potentially causal DR associations with type 1 diabetes, this list of residuals is expected to include corresponding causal residues in this study population.

Identifying coevolutionary patterns in human leukocyte antigen (HLA) molecules

The antigenic peptide, major histocompatibility complex molecule (MHC; also called human leukocyte antigen, HLA), coreceptor CD8, or CD4 and T-cell receptor (TCR) function as a complex to initiate effectors' mechanisms of the immune system. The tight functional and physical interaction among these molecules may have involved strong coevolution links among domains within and between proteins. Despite the importance of unraveling such dependencies to understand the arms race of host-pathogen interaction, no previous studies have aimed at achieving such an objective. Here, we perform an exhaustive coevolution analysis and show that indeed such dependencies are strongly shaping the evolution and probably the function of these molecules. We identify intramolecular coevolution in HLA class I and II at domains important for their immune activity. Most of the amino acid sites identified to be coevolving in HLAI have been also detected to undergo positive Darwinian selection highlighting therefore their adaptive value. We also identify coevolution among antigen-binding pockets (P1-P9) and among these and TCR-binding sites. Conversely to HLAI, coevolution is weaker in HLAII. Our results support that such coevolutionary patterns are due to selective pressures of host-pathogen coevolution and cooperative binding of TCRs, antigenic peptides, and CD8/CD4 to HLAI and HLAII.

Human leukocyte antigen class II associations with hepatitis C virus clearance and virus-specific CD4 T cell response among Caucasians and African Americans

The outcome of hepatitis C virus (HCV) infection has been associated with antiviral CD4 T cell response, human leukocyte antigens (HLA) class II genotypes, and ethnicity. However, HLA class II molecules restrict the nature of CD4 T cell response, and HLA distributions differ between ethnic groups. In this study, we asked whether HLA class II genotypes associated with HCV clearance are shared between Caucasian and African Americans and whether they contribute to enhanced antiviral CD4 T cell response. In a cohort of 93 HCV-seropositive subjects from Northeast America with defined ethnicity, virological outcome, and HCV-specific CD4 T cell proliferation, we confirm the previously reported associations between HCV clearance and two HLA types (DQB1*03, DRB1*11) while identifying a new association with DRB3*02. Strikingly, these associations were identified only among Caucasian [DQB1*03: odds ratio (OR), 10.4; P = 0.031, DRB1*11: OR, 7.0, P = 0.019; DRB3*02: OR, 8.3, P = 0.005; DQB1*03-DRB3*02: OR, 13.5, P = 0.001) but not among African American patients. Furthermore, although HLA DQB1*03, DRB1*11, and DRB3*02 genotypes were associated with increased HCV-specific CD4 T cell response in univariate analyses, these associations were lost when controlling for virological outcomes.

CONCLUSION

We conclude that the immunogenetic basis for HCV clearance differs between ethnic groups and that the association between HLA class II and HCV clearance is not directly explained by antiviral CD4 T cell response.

HLA-B, -DRB1/3/4/5, and -DQB1 gene polymorphisms in human immunodeficiency virus-related Kaposi's sarcoma

Polymorphisms of genes in the human leukocyte antigen (HLA) complex, particularly those encoding HLA-DR, have been suggested as markers of susceptibility to Kaposi's sarcoma (KS). We conducted a case-control study comparing 147 homosexual men who developed KS after infection by human immunodeficiency virus-1 (HIV-1) and human herpes virus 8 (HHV8) with 147 matched dually infected men without HIV-associated KS (HIV-KS) from the Multicenter AIDS Cohort Study. HLA-B, DRB1, DRB3, DRB4, DRB5, and DQB1 polymorphisms were examined by high-resolution DNA-based methods. Differences in distributions of genetic variants were tested by conditional logistic regression. Previously reported relationships with HLA-DRB1 alleles could not be confirmed. Instead, other associations were observed. In univariate analysis, KS was weakly associated with B*2702/5 (odds ratio (OR)=0.40, 95% confidence interval (CI)=0.18-0.91). Similar or stronger associations, positive or negative, were seen for haplotypes containing class II alleles: DRB1*1302-DQB1*0604 (OR=3.67, 95% CI=1.02-13.1), DRB4 (DR53) haplotype family members [OR=0.52, 95% CI=0.32-0.85], and DRB3 (DR52) haplotype family members (OR=1.69, 95% CI=1.07-2.67). The B*1402-DRB1*0102 haplotype, which invariably contains the V281L mutation in the 21-hydroxylase gene governing adrenal steroid biosynthesis, occurred in five cases and one control (OR=5.0, 95% CI=0.58-42.8). In a final multivariable analysis, only DRB1*1302-DQB1*0604 (OR=6.43, 95% CI=1.28-32.3, P=0.02) remained significantly associated with KS. Associations of HLA-DRB families with HIV-KS could reflect underlying immune dysregulation. The HLA B*1402-DRB1*0102 haplotype associated with increased risk of KS might represent an antigen-presenting pathway unfavorable for immune response to HHV8. Alternatively, the relationship might hold a clue to the predilection of KS for men because that haplotype harbors the mutant form of the 21-hydroxylase gene.

Cross-reactive recognition of human and primate cytomegalovirus sequences by human CD4 cytotoxic T lymphocytes specific for glycoprotein B and H

Although the importance of CD4+ T cell responses to human cytomegalovirus (HCMV) has recently been recognized in transplant and immunosuppressed patients, the precise specificity and nature of this response has remained largely unresolved. In the present study we have isolated CD4+ CTL which recognize epitopes from HCMV glycoproteins gB and gH in association with two different HLA-DR antigens, DRA1*0101/DRB1*0701 (DR7) and DRA1*0101/DRB1*1101 (DR11). Comparison of amino acid sequences of HCMV isolates revealed that the gB and gH epitope sequences recognized by human CD4+ T cells were not only conserved in clinical isolates from HCMV but also in CMV isolates from higher primates (chimpanzee, rhesus and baboon). Interestingly, these epitope sequences from chimpanzee, rhesus and baboon CMV are efficiently recognized by human CD4+ CTL. More importantly, we show that gB-specific T cells from humans can also efficiently lyse peptide-sensitized Patr-DR7+ cells from chimpanzees. These findings suggest that conserved gB and gH epitopes should be considered while designing a prophylactic vaccine against HCMV. In addition, they also provide a functional basis for the conservation of MHC class II lineages between humans and Old World primates and open the possibility for the use of such primate models in vaccine development against HCMV.

Interactions between major histocompatibility complex class II surface expression and HIV: implications for pathogenesis

Although it has been almost 20 years since the first cases of acquired immunodeficiency syndrome (AIDS) were documented, the pathogenesis is still not completely understood. Interactions between major histocompatibility complex (MHC) Class I and human immunodeficiency virus (HIV), resulting in down-regulation of MHC-I surface expression, have been reported to contribute to pathogenesis by suppressing the host's immune response. Interactions between MHC Class II and HIV have also been described, but it is unclear how these contribute to the pathogenesis. MHC-II surface expression on HIV-infected monocytes and monocytic cell lines has been described to be increased as well as decreased when compared to uninfected control monocytes. HIV-specific mechanisms appear to down-regulate MHC-II expression on blood monocytes during HIV-1 infection, whereas host mechanisms up-regulate MHC-II expression in response to infection of blood monocytes as well as brain macrophages. A balance between these two may determine MHC-II expression levels in individual patients. Altogether, HIV seems to be able to benefit from both low and high levels of MHC-II surface expression. The first results in reduced immune surveillance of the host, allowing the virus to replicate faster; the second increases infectivity of the virus as a result of higher MHC-II density on macrophages and virion particles.

Antigen-induced T cell death is regulated by CD4 expression

Activation induced cell death (AICD) is a major physiologic pathway that regulates T cell homeostasis. In CD4 T cells, AICD is mediated mainly through Fas/FasL interactions. Although TCR occupancy triggers AICD, the contribution of its tightly associated CD4 coreceptor to the process that leads to AICD is not known. Here we show that CD4 molecule plays an essential regulatory role of TCR dependent AICD. Loss of CD4 rendered activated 5kc T cell hybridoma resistant to AICD. The resistance of CD4 negative 5kc T cells to AICD was due to selective inhibition of FasL expression and it could be reversed by addition of recombinant FasL. Furthermore, a direct functional link between CD4 and FasL was demonstrated by induction of FasL upon CD4 crosslinking in a TCR independent fashion. The importance of CD4 interaction with MHC/peptide complex in mediating AICD was also evident in normal T cells that could survive chronic stimulation with anti-CD3 but died after short period of proliferation after stimulation with MHC/peptide. Thus it appears that AICD is controlled by the CD4 molecule via regulation of FasL expression. These findings have important implications for our understanding of mechanisms of peripheral tolerance as well as pathogenesis of autoimmune diseases.

Lack of coreceptor allows survival of chronically stimulated double-negative alpha/beta T cells: implications for autoimmunity

Lymphoproliferative diseases are characterized by massive accumulation of CD4(-)CD8(-)B220(+) (double-negative [DN]) T cells in peripheral organs. Although evidence indicates these cells are derived from mature autoreactive alpha/beta T cells, the significance of coreceptor downregulation is not known. In this study, we examined the role CD4 coreceptor plays in the survival of repeatedly stimulated T cells. CD4(+/+) and CD4(-/-) T cells from AND T cell receptor (TCR) transgenic mice exhibited similar phenotypes after antigenic stimulation, but the CD4(-/-) T cells survived in much larger numbers than the CD4(+/+) cells upon primary and secondary major histocompatibility complex (MHC)/peptide stimulation. Enhanced survival of CD4(-/-) T cells was due to decreased apoptosis rather than enhanced proliferation. Similarly, circumvention of the CD4/MHC interaction by using a surrogate TCR ligand that does not engage CD4 led to significant enhancement of CD4(+/+) cells than when stimulated with MHC/peptide. Finally, we generated DN B220(+) T cells using an in vitro model system and showed they were more tolerant to chronic stimulation than CD4(+/+) cells. Together, these results indicate that coreceptor engagement controls expansion of normal T cells. In the absence of coreceptor, T cells survive chronic stimulation and express B220 as seen in autoimmune lymphoproliferative diseases.

Immunoglobulin superfamily proteins: structure, mechanisms, and drug discovery

We review the recent progress made in our laboratories in structure-based drug design targeting proteins of the immunoglobulin superfamily (IgSF). We will focus on the CD4 protein, which is involved in T cell function, as a specific example of how the general concept and methodologies can be applied. Recent studies of CD4 structure and function have revealed new insight into possible mechanisms for CD4 self-association and its role in binding to major histocompatibility complex (MHC) class II molecules and initiation of T cell activation. This has led to the formulation of a hypothetical model of co-oligomerization of CD4, MHC class II, and T cell receptor (TCR). Such a basic understanding of CD4 structure and mechanisms has aided the development of a new generation of potential immunotherapeutics targeting specific CD4 surface functional sites. The design and discovery of small molecular inhibitors of CD4 and other IgSF proteins, in peptide, peptidomimetic, and nonpeptidic organic forms have opened new avenues for chemical research in which peptide, organic, and more recently combinatorial chemistry techniques can be used to further develop these promising lead analogs into a new generation of effective pharmaceuticals.

Allele-specific and peptide-dependent recognition of swine leukocyte antigen class I by human cytotoxic T-cell clones

BACKGROUND

The T-cell mediated immune responses play a major role in xenograft rejection. However, the mechanisms behind human T-cell recognition of porcine xenoantigens remain to be elucidated.

METHODS

Human CD8+ T-cell lines were generated against porcine aortic endothelial cells (PAECs) from y/y and z/z haplotypes of Yucatan inbred swine. T-cell clones were obtained by limiting dilution. The human T-cell receptor (TCR)-swine leukocyte antigen (SLA) class I interaction was characterized.

RESULTS

The human CD8+ T-cell mediated direct recognition of PAECs was SLA haplotype-specific. The haplotype specificity was restricted by the SLA class I allelic polymorphism. To characterize the role of SLA-bound peptides in the human TCR-SLA class I interaction, we stripped peptides from SLA molecules by a brief acid treatment. Using z/z-specific CD8+ T cells as effectors, we demonstrated that the acid-treatment, which stripped SLA molecules of bound peptides, decreased the lysis of PAECs by 72%. Addition of peptides eluted from affinity purified z/z SLA class I molecules, but not from the irrelevant y/y SLA class I, restored the lysis of acid-treated z/z PAECs. In addition, the lysis of a human HLA class I negative cell line, 721.221, transfected with a relevant SLA class I allele derived from the z/z haplotype, was significantly increased with the addition of relevant z/z peptides. These experiments indicated that both SLA class I and bound peptides were required for recognition by human CD8+ T cells. Cloning studies identified two groups of xenoreactive T-cell clones. Group I clones recognized distinct porcine peptides in the context of SLA class I molecules, whereas group II clones recognized human endogenous cross-reactive peptides presented by SLA class I.

CONCLUSIONS

Our results demonstrated that, despite the differences in MHC molecules between species, human T-cell recognition of porcine MHC is similar to direct allo-recognition, that is, human TCR recognizes xenogeneic SLA-peptide complexes.

BALB/c Invariant Chain Mutant Mice Display Relatively Efficient Maturation of CD4+ T Cells in the Periphery and Secondary Proliferative Responses Elicited upon Peptide Challenge

Allelic differences are known to influence many important aspects of class II biosynthesis, including subunit assembly, Ii chain associations, and DM-mediated peptide loading. Mutant mouse strains lacking Ii chain expression have been previously studied on mixed genetic backgrounds. The present experiments describe cellular and functional characteristics of congenic BALB/c Ii chain mutants. As expected, class II surface expression was markedly decreased, but in contrast to I-Ad-transfected cell lines, serological analysis of BALB/c Ii chain-deficient spleen cells gave no evidence for discordant expression of class II conformational epitopes. Thus, we conclude that properly folded class II molecules are exported via the Ii chain-independent pathway. Functional assays demonstrate consistently superior peptide-loading capabilities, suggesting that these I-Ad molecules are empty or occupied by an easily displaced peptide(s). Defective B cell development was observed for three mutant strains established on diverse genetic backgrounds. Ii chain function is also essential for optimal class II surface expression by mature splenic dendritic cells. Surprisingly, we observe in BALB/c Ii chain mutants, relatively efficient maturation of CD4+ T cells in the periphery and secondary proliferative responses elicited upon peptide challenge. The milder phenotype displayed by BALB/c Ii chain mutants in comparison with class II functional defects previously described for mouse strains lacking Ii chain is likely to have an effect on disease susceptibility.

Immunosuppressory mini-regions of HLA-DP and HLA-DR

Our previous studies showed, that the,TPQRGDVYT, QRGDVYT and RGDVYT fragments, located in the beta164-172 loop of HLA-DQ, strongly suppress the humoral and cellular immune response, while their shorter analogs, RGDV, RGDVY, and QRGDVY, show only weak stimulatory activity in respect to humoral immunological response. The fragments contain the RGDVY sequence that is analogous to thymopentin (pentapeptide RKDVY, an immune system activator) as well as the RGD sequence, known for its importance for cellular association phenomena. Based on the crystal structure of HLA-DR1, we also designed and synthesized a cyclic analog C*RGDVYC* (where C* indicates Cys participating in disulfide bridge) with restricted conformation, which strongly suppresses both humoral and cellular immune response. In the present study we synthesized and tested the immunological properties of the linear and cyclic HLA-DP and HLA-DR counterparts of all the above HLA-DQ fragments. Although the results show that the linear HLA-DP fragments possess moderate immunosuppressory potency, their conformationally restricted analog, C*QGDVYC*C shows a considerable suppression of both humoral and cellular immune response. The nonapeptide fragment of HLA-DR, VPRSGEVYT and particularly its cyclic analog C*SGEVYC*, are strong suppressors of the humoral response.

A novel HLA-DR12 allele (DRB1*1206) found in a Korean B-cell line

At least 6 HLA-DRB1*12 alleles have been identified to date with nucleotide polymorphism occurring at codons 37, 57-58, 60, 67, 85 and 87. In this report, we describe the identification of another new HLA-DRB1*12 allele: DRB1*1206. This novel allele was found in an Epstein-Barr virus (EBV)-transformed Korean B-cell line "K-KT" having the HLA-phenotype A3, 24; B44, 61; Cw3; Bw4, 6; DR12, 13 during full-length cDNA isolation for cell line characterization and for production of HLA-DR recombinant proteins. The allele was identified initially by cycle sequencing of subcloned HLA-DRB full-length cDNA.

Ligation of MHC class II molecules differentially upregulates TNF beta gene expression in B cell lines of different MHC class II haplotypes

Although the production of selected cytokines by B cells is important for their regulation, little is known about MHC class II-induced cytokine expression in these cells. We designed the present studies to investigate MHC class II-mediated TNF-beta gene expression in 19 EBV-transformed homozygote B cell lines at similar stage of differentiation but presenting different MHC class II haplotypes. Our results demonstrate that in contrast to PMA, engagement of MHC class II with staphylococcal enterotoxin A (SEA), a natural ligand, or with anti-HLA-DR mAb L243, stimulates TNF-beta gene expression in some but not all B cell lines. The differential stimulation of TNF-beta gene expression via MHC class II was not due to the cells MHC class II expression level, nor to their capacity to bind the ligands as evidenced by SEA binding affinity studies. Together these results demonstrate that ligation of MHC class II molecules can stimulate TNF-beta gene expression in a B cell line-dependent manner. The differential cytokine gene expression might be due to an influence of MHC class II haplotype either by a linkage disequilibrium with TNF-beta gene or by a differential association with effector or cell surface molecules.

CD4 dimerization and oligomerization: implications for T-cell function and structure-based drug design

Recent studies of CD4 structure and function have revealed possible mechanisms for CD4 self-association, with implications for its role in T-cell activation. Here, the authors discuss the formulation of a hypothetical three-dimensional model of CD4 oligomerization and how it impacts on the understanding of T-cell function and rational drug design targeting specific CD4 surface functional sites.

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

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

T cell response to myelin basic protein in the context of the multiple sclerosis-associated HLA-DR15 haplotype: peptide binding, immunodominance and effector functions of T cells

In this study, we evaluated the role of the two functional HLA-DR heterodimers, DR2a (DR alpha paired with the beta chain encoded by DRB5*0101) and DR2b (DR alpha paired with the beta chain encoded by DRB1*1501), that are coexpressed in the multiple sclerosis (MS)-associated haplotype HLA-DR15 Dw2, in presenting myelin basic protein (MBP) peptides to MBP-specific T cell lines (TCL). Our results show that both HLA-DR molecules serve as restriction elements for HLA-DR15-restricted TCL. Slightly higher numbers of TCL use DR2a as restriction element, and the epitopes contained in the immunodominant C-terminal region (131-159) are uniquely restricted by DR2a. The immunodominant middle epitope (81-99) is recognized in the context of both DR2a and DR2b, but this specificity strongly dominates the DR2b-restricted T cell response. Overall, immunodominance in the MBP-specific T cell response correlated well with peptide binding to DR2a or DR2b, demonstrating that the affinity of MHC-peptide interactions is important for shaping the T cell response to this autoantigen. Furthermore, we show that binding of the middle MBP peptide to HLA-DR15 molecules prevents cleavage by cathepsin D, a protease abundantly found in endosomal processing compartments, and thus contributes to its immunodominance. Surprisingly, the restriction element employed by MBP-specific T cell clones influenced the effector function (i.e., cytotoxic activity) of T cells irrespective of their peptide fine specificity.

The Acquisition of Host-Derived Major Histocompatibility Complex Class II Glycoproteins by Human Immunodeficiency Virus Type 1 Accelerates the Process of Virus Entry and Infection in Human T-Lymphoid Cells

Infection by human immunodeficiency virus type 1 (HIV-1) results in a progressive depletion of CD4+ T lymphocytes, leading to fatal immunodeficiency. The mechanisms causing the marked loss of CD4+ T lymphocytes are incompletely understood. However, several lines of evidence indicate that direct cytopathology mediated by HIV-1 is a key element in such CD4+ T-cell depletion. In this study, we investigated whether the previously reported incorporation of host-derived major histocompatibility class II glycoproteins (MHC-II) on HIV-1 can alter its replicative capacity. To achieve this goal, virus stocks were produced in parental MHC-II–expressing RAJI cells and in MHC-II–negative RAJI mutants (RM3), both of which have been stably transfected with human CD4 cDNA to allow productive infection with HIV-1. An enhancement of the rate/efficiency of virus entry was seen after infection with normalized amounts of virions carrying host-derived MHC-II on their surface as compared with inoculation with virions devoid of cellular MHC-II. Data from time-course and infectivity experiments showed that the kinetics of infection were more rapid for virions bearing host-derived MHC-II glycoproteins than for MHC-II–free HIV-1 particles. These results suggest that virally embedded cellular MHC-II glycoproteins are functional and can have a positive effect on early events in the virus replicative cycle. Therefore, we show that the acquisition of cellular MHC-II glycoproteins by HIV-1 can modify its biologic properties and might, consequently, influence the pathogenesis of this retroviral disease.

The Acquisition of Host-Derived Major Histocompatibility Complex Class II Glycoproteins by Human Immunodeficiency Virus Type 1 Accelerates the Process of Virus Entry and Infection in Human T-Lymphoid Cells

Infection by human immunodeficiency virus type 1 (HIV-1) results in a progressive depletion of CD4+ T lymphocytes, leading to fatal immunodeficiency. The mechanisms causing the marked loss of CD4+ T lymphocytes are incompletely understood. However, several lines of evidence indicate that direct cytopathology mediated by HIV-1 is a key element in such CD4+ T-cell depletion. In this study, we investigated whether the previously reported incorporation of host-derived major histocompatibility class II glycoproteins (MHC-II) on HIV-1 can alter its replicative capacity. To achieve this goal, virus stocks were produced in parental MHC-II–expressing RAJI cells and in MHC-II–negative RAJI mutants (RM3), both of which have been stably transfected with human CD4 cDNA to allow productive infection with HIV-1. An enhancement of the rate/efficiency of virus entry was seen after infection with normalized amounts of virions carrying host-derived MHC-II on their surface as compared with inoculation with virions devoid of cellular MHC-II. Data from time-course and infectivity experiments showed that the kinetics of infection were more rapid for virions bearing host-derived MHC-II glycoproteins than for MHC-II–free HIV-1 particles. These results suggest that virally embedded cellular MHC-II glycoproteins are functional and can have a positive effect on early events in the virus replicative cycle. Therefore, we show that the acquisition of cellular MHC-II glycoproteins by HIV-1 can modify its biologic properties and might, consequently, influence the pathogenesis of this retroviral disease.

Quantitative but not qualitative variation in MHC class II alters CD4 interaction and influences T cell repertoire formation

The influence of the interaction between CD4 and MHC class II molecules on selection of the T cell repertoire was studied in transgenic mice expressing human or human/mouse hybrid MHC class II beta chains. Either wild-type DR beta chains (DR1 beta) or hybrid beta chains comprising the beta1 domain of DR and the beta2, transmembrane, and intracytoplasmic domains of I-E (DRbeta 1Ebeta2) were introduced into and expressed in transgenic mice as a heterodimer with endogenous I-E alpha. Mice expressing low levels of DR1beta:I-E alpha or those expressing low or higher levels of the hybrid DRbeta 1Ebeta2:I-E alpha were studied. Immunization with a suboptimal dose of influenza nucleoprotein peptide exposed a fivefold lower frequency of DR-restricted, peptide-specific, IL-2-secreting T cells in the mice with low-level expression of DRbeta1 Ebeta2:I-E alpha when compared to mice expressing the same molecule at higher levels. The frequency in DRbeta wild-type mice was only twofold lower than that measured in mice with comparable levels of expression of DRbeta 1Ebeta2. These results suggest that positive selection is sensitive to quantitative variation in MHC class II density, unmasked when antigen is limiting, but is relatively insensitive to qualitative variation in the MHC class II: CD4 interaction.

The presence of host-derived HLA-DR1 on human immunodeficiency virus type 1 increases viral infectivity

Human immunodeficiency virus type 1 (HIV-1) incorporates several host cell components when budding out of the infected cell. One of the most abundant host-derived molecules acquired by HIV-1 is the HLA-DR determinant of the major histocompatibility complex class II (MHC-II) molecules. The fact that CD4 is the natural ligand of MHC-II prompted us to determine if such virally embedded cellular components can affect the biology of the virus. Herein, we report for the first time that the incorporation of cellular HLA-DR1 within HIV-1 enhances its infectivity. This observation was made possible with virions bearing or not bearing on their surfaces host-derived HLA-DR1 glycoproteins. Such virus stocks were prepared by a transient-expression system based on transfection of 293T cells with a recombinant luciferase-encoding HIV-1 molecular clone along with plasmids encoding the alpha and beta chains of HLA-DR1. Cell-free virions recovered from transfected cells were shown to have efficiently incorporated host-derived HLA-DR1 glycoproteins. Infectivity was increased by a factor of 1.6 to 2.3 for virions bearing on their surfaces host-derived HLA-DR1. The observed enhancement of HIV-1 infectivity was independent of the virus stocks used and was seen in several T-lymphoid cell lines, in a premonocytoid cell line, and in primary peripheral blood mononuclear cells. Finally, we determined that the presence of virion-bound cellular HLA-DR1 is associated with faster kinetics of virus infection. Taken together, these results suggest that HLA-DR-1-bearing HIV-1 particles had a greater infectivity per picogram of viral p24 protein than HLA-DR1-free virions.

Functional significance of polymorphism among MHC class II gene promoters

The functional significance of polymorphism among MHC class II promoters in man and mouse is here reviewed, mainly in terms of the hypothesis of differential expression. The hypothesis proposes that differences between antigen-presenting cells in MHC class II expression exert a co-dominant effect on the Th1-Th2 cytokine balance, such that class II molecules of one type come to control to a greater extent the production of one group of cytokines, and those of another type the production of the alternative group. The survey deals with the influence of signal strength and antigen-presenting cell type on T-cell subset differentiation; functional differences between MHC class II molecules not obviously related to determinant selection; disease protection mediated by HLA alleles; mechanisms possibly responsible for allotypic and isotypic bias; overdominance (heterozygous advantage) in selection for expression of class II alleles; MHC class II promoter structure and function; inter-locus and inter-allele variability within human MHC class II gene upstream regulatory regions; a comparison of these polymorphisms in mouse and man; read-out of class II promoter function; and a comparison with expression of MHC class I. We conclude that the evidence that this variation is functionally active (i.e. controls expression) is increasing, but is not yet compelling. The crucial test still to come, we suggest, is whether or not the biological effects attributable to this polymorphism will line up with molecular studies on expression.

HLA-DR4-IE chimeric class II transgenic, murine class II-deficient mice are susceptible to experimental allergic encephalomyelitis

To investigate the development of HLA-DR-associated autoimmune diseases, we generated transgenic (Tg) mice with HLA-DRA-IE alpha and HLA-DRB1*0401-IE beta chimeric genes. The transgene-encoded proteins consisted of antigen-binding domains from HLA-DRA and HLA-DRB1*0401 molecules and the remaining domains from the IE(d)-alpha and IE(d)-beta chains. The chimeric molecules showed the same antigen-binding specificity as HLA-DRB1*0401 molecules, and were functional in presenting antigens to T cells. The Tg mice were backcrossed to MHC class II-deficient (IA beta-, IE alpha-) mice to eliminate any effect of endogenous MHC class II genes on the development of autoimmune diseases. As expected, IA alpha beta or IE alpha beta molecules were not expressed in Tg mice. Moreover, cell-surface expression of endogenous IE beta associated with HLA-DRA-IE alpha was not detectable in several Tg mouse lines by flow cytometric analysis. The HLA-DRA-IE alpha/HLA-DRB1*0401-IE beta molecules rescued the development of CD4+ T cells in MHC class II-deficient mice, but T cells expressing V beta 5, V beta 11, and V beta 12 were specifically deleted. Tg mice were immunized with peptides, myelin basic protein (MBP) 87-106 and proteolipid protein (PLP) 175-192, that are considered to be immunodominant epitopes in HLA-DR4 individuals. PLP175-192 provoked a strong proliferative response of lymph node T cells from Tg mice, and caused inflammatory lesions in white matter of the CNS and symptoms of experimental allergic encephalomyelitis (EAE). Immunization with MBP87-106 elicited a very weak proliferative T cell response and caused mild EAE. Non-Tg mice immunized with either PLP175-192 or MBP87-106 did not develop EAE. These results demonstrated that a human MHC class II binding site alone can confer susceptibility to an experimentally induced murine autoimmune disease.