Public TCR use by herpes simplex virus-2-specific human CD8 CTLs

Recombination of germline TCR alpha and beta genes generates polypeptide receptors for MHC peptide. Ag exposure during long-term herpes simplex infections may shape the T cell repertoire over time. We investigated the CD8 T cell response to HSV-2 in chronically infected individuals by sequencing the hypervariable regions encoding TCR alpha and beta polypeptides from T cell clones recognizing virion protein 22 aa 49-57, an immunodominant epitope. The most commonly detected TCRBV gene segment, found in four of five subjects and in 12 of 50 independently derived T cell clones, was TCRBV12-4. Nineteen to seventy-two percent of tetramer-binding cells in PBMCs were stained ex vivo with a TCRBV12 mAb. Three alpha-chain and three beta-chain public TCR sequences were shared between individuals. Public heterodimers were also detected. Promiscuous pairing of a specific TCRVA1-1 sequence with several different TCRB polypeptides was observed, implying a dominant structural role for the TCRA chain for these clonotypes. Functional avidity for cytotoxicity and IFN-gamma release was relatively invariant, except for one subject with both high avidity and unique TCR sequences and lower HSV-2 shedding. These data indicate that the CD8 response to a dominant alpha-herpesvirus epitope converges on preferred TCR sequences with relatively constant functional avidity.

Soluble HLA-G and HLA-A,-B,-C serum levels in patients with allergic rhinitis

BACKGROUND

Allergic rhinitis (AR) is characterized by Th2-polarized immune response. Soluble HLA (sHLA) molecules play an immunomodulatory activity. So far, however, no study investigated them in AR.

OBJECTIVE

The aim of this study was to evaluate sHLA-G and sHLA-A,-B,-C serum levels in AR patients with pollen allergy and in a group of healthy controls.

METHODS

Forty-nine AR patients were enrolled. A group of healthy nonallergic subjects was considered as control. sHLA-G and sHLA-A,-B,-C serum levels were determined by immunoenzymatic method. The study was conducted during the winter, such as outside the pollen season.

RESULTS

Allergic patients had significantly higher levels of both sHLA-G (P < 0.0001) and sHLA-A,-B,-C (P = 0.011) molecules than normal controls. Moreover, there was a significant relationship between these two soluble molecules (r = 0.69) in allergic patients.

CONCLUSION

The present study provides the first evidence that both sHLA-G and sHLA-A,-B,-C serum levels are significantly increased in AR patients with pollen allergy.

Expression, purification and preliminary X-ray crystallographic analysis of the human major histocompatibility antigen HLA-B*1402 in complex with a viral peptide and with a self-peptide

The product of the human major histocompatibility (HLA) class I allele HLA-B*1402 only differs from that of allele HLA-B*1403 at amino-acid position 156 of the heavy chain (Leu in HLA-B*1402 and Arg in HLA-B*1403). However, both subtypes are known to be differentially associated with the inflammatory rheumatic disease ankylosing spondylitis (AS) in black populations in Cameroon and Togo. HLA-B*1402 is not associated with AS, in contrast to HLA-B*1403, which is associated with this disease in the Togolese population. The products of these alleles can present peptides with Arg at position 2, a feature shared by a small group of other HLA-B antigens, including HLA-B*2705, the prototypical AS-associated subtype. Complexes of HLA-B*1402 with a viral peptide (RRRWRRLTV, termed pLMP2) and a self-peptide (IRAAPPPLF, termed pCatA) were prepared and were crystallized using polyethylene glycol as precipitant. The complexes crystallized in space groups P2(1) (pLMP2) and P2(1)2(1)2(1) (pCatA) and diffracted synchrotron radiation to 2.55 and 1.86 A resolution, respectively. Unambiguous solutions for both data sets were obtained by molecular replacement using a peptide-complexed HLA-B*2705 molecule (PDB code 1jge) as a search model.

Expression and Functional Analysis of Human Leukocyte Antigen Class I Antigen-Processing Machinery in Medulloblastoma

Defects in the expression and/or function of the human leukocyte antigen (HLA) class I antigen-processing machinery (APM) components are found in many tumor types. These abnormalities may have a negative impact on the interactions of tumor cells with host's immune system and on the outcome of T cell-based immunotherapy. To the best of our knowledge, no information is available about APM component expression and functional characteristics in human medulloblastoma cells (Mb). Therefore, in the present study, we have initially compared the expression of APM components in Mb, an embryonal pediatric brain tumor with a poor prognosis, with that in noninfiltrating astrocytic pediatric tumors, a group of differentiated brain malignancies with favorable prognosis. LMP2, LMP7, calnexin, beta2-microglobulin-free heavy chain (HC) and beta2-microglobulin were down-regulated or undetectable in Mb lesions, but not in astrocytic tumors or normal fetal cerebellum. Two Mb cell lines (DAOI and D283) displayed similar but not superimposable defects in APM component expression as compared with primary tumors. To assess the functional implications of HLA class I APM component down-regulation in Mb cell lines, we tested their recognition by HLA class I antigen-restricted, tumor antigen (TA)-specific CTL, generated by stimulations with dendritic cells that had been transfected with Mb mRNA. The Mb cell lines were lysed by TA-specific CTL in a HLA-restricted manner. Thus, defective expression of HLA class I-related APM components in Mb cells does not impair their ability to present TA to TA-specific CTL. In conclusion, these results can contribute to optimize T cell-based immunotherapeutic strategies for Mb treatment.

HLA-B*2704, an Allotype Associated with Ankylosing Spondylitis, Is Critically Dependent on Transporter Associated with Antigen Processing and Relatively Independent of Tapasin and Immunoproteasome for Maturation, Surface Expression, and T Cell Recognition: Relationship to B*2705 and B*2706

B*2704 is strongly associated to ankylosing spondylitis in Asian populations. It differs from the main HLA-B27 allotype, B*2705, in three amino acid changes. We analyzed the influence of tapasin, TAP, and immunoproteasome induction on maturation, surface expression, and T cell allorecognition of B*2704 and compared some of these features with B*2705 and B*2706, allotypes not associated to disease. In the tapasin-deficient .220 cell line, this chaperone significantly influenced the extent of folding of B*2704 and B*2705, but not their egress from the endoplasmic reticulum. In contrast, B*2706 showed faster folding and no accumulation in the endoplasmic reticulum in the absence of tapasin. Surface expression of B*2704 was more tapasin dependent than B*2705. However, expression of free H chain decreased in the presence of this chaperone for B*2705 but not B*2704, suggesting that more suboptimal ligands were loaded on B*2705 in the absence of tapasin. Despite its influence on surface expression, tapasin had little effect on allorecognition of B*2704. Both surface expression and T cell recognition of B*2704 were critically dependent on TAP, as established with TAP-deficient and TAP-proficient T2 cells. Both immunoproteasome and surface levels of B*2704 were induced by IFN-gamma, but this had little effect on allorecognition. Thus, except for the differential effects of tapasin on surface expression, the tapasin, TAP, and immunoproteasome dependency of B*2704 for maturation, surface expression, and T cell recognition are similar to B*2705, indicating that basic immunological features are shared by the two major HLA-B27 allotypes associated to ankylosing spondylitis in human populations.

HLA-B*5701 typing by sequence-specific amplification: validation and comparison with sequence-based typing

Susceptibility to abacavir hypersensitivity (ABC HSR) is strongly associated with alleles carried on the 57.1 ancestral haplotype including HLA-B*5701 and Hsp70 Hom M493T. In one study, prospective testing for HLA-B*5701 and exclusion of individuals carrying this allele, from receiving abacavir, substantially lowered the incidence of ABC HSR to 0% (95% confidence interval 0-0.075%). The presence of HLA-B*5701 is usually detected by standard serological tests and by molecular genetic methods such as sequence-based typing (SBT). While the former test cannot discriminate between HLA-B57 subtypes, the expensive SBT may not be readily available in all laboratories. Hence, an alternate method was developed to detect HLA-B*5701 using allele and group-specific polymerase chain reaction-sequence-specific primers (PCR-SSP) typing. This PCR-SSP-typing method positively amplified all HLA-B*5701 alleles in concordance with their SBT-assigned typing. This multiplexed SSP assay was able to distinguish between HLA-B*5701 (n = 10) and closely related HLA-B57 alleles B*5702 (n = 2), -B*5703 (n = 1), -B*5704 (n = 1) alleles and non-HLA-B*57 alleles (n = 61). In conclusion, this method of HLA-B*5701 detection is a rapid and accurate typing method with high specificity, sensitivity and reproducibility.

HIV-1 viral escape in infancy followed by emergence of a variant-specific CTL response

Mutational escape from the CTL response represents a major driving force for viral diversification in HIV-1-infected adults, but escape during infancy has not been described previously. We studied the immune response of perinatally infected children to an epitope (B57-TW10) that is targeted early during acute HIV-1 infection in adults expressing HLA-B57 and rapidly mutates under this selection pressure. Viral sequencing revealed the universal presence of escape mutations within TW10 among B57- and B5801-positive children. Mutations in TW10 and other B57-restricted epitopes arose early following perinatal infection of B57-positive children born to B57-negative mothers. Surprisingly, the majority of B57/5801-positive children exhibited a robust response to the TW10 escape variant while recognizing the wild-type epitope weakly or not at all. These data demonstrate that children, even during the first years of life, are able to mount functional immune responses of sufficient potency to drive immune escape. Moreover, our data suggest that the consequences of immune escape may differ during infancy because most children mount a strong variant-specific immune response following escape, which is rarely seen in adults. Taken together, these findings indicate that the developing immune system of children may exhibit greater plasticity in responding to a continually evolving chronic viral infection.

Immune selection of hot-spot beta 2-microglobulin gene mutations, HLA-A2 allospecificity loss, and antigen-processing machinery component down-regulation in melanoma cells derived from recurrent metastases following immunotherapy

Scanty information is available about the mechanisms underlying HLA class I Ag abnormalities in malignant cells exposed to strong T cell-mediated selective pressure. In this study, we have characterized the molecular defects underlying HLA class I Ag loss in five melanoma cell lines derived from recurrent metastases following initial clinical responses to T cell-based immunotherapy. Point mutations in the translation initiation codon (ATG-->ATA) and in codon 31 (TCA-->TGA) of the beta(2)-microglobulin (beta(2)m) gene were identified in the melanoma cell lines 1074MEL and 1174MEL, respectively. A hot-spot CT dinucleotide deletion within codon 13-15 was found in the melanoma cell lines 1106MEL, 1180MEL, and 1259MEL. Reconstitution of beta(2)m expression restored HLA class I Ag expression in the five melanoma cell lines; however, the HLA-A and HLA-B,-C gene products were differentially expressed by 1074MEL, 1106MEL, and 1259MEL cells. In addition, in 1259MEL cells, the Ag-processing machinery components calnexin, calreticulin, and low m.w. polypeptide 10 are down-regulated, and HLA-A2 Ags are selectively lost because of a single cytosine deletion in the HLA-A2 gene exon 4. Our results in conjunction with those in the literature suggest the emergence of a preferential beta(2)m gene mutation in melanoma cells following strong T cell-mediated immune selection. Furthermore, the presence of multiple HLA class I Ag defects within a tumor cell population may reflect the accumulation of multiple escape mechanisms developed by melanoma cells to avoid distinct sequential T cell-mediated selective events.

CD4 and CD8 T-lymphocyte recognition of prostate specific antigen in granulomatous prostatitis

In order to develop immunotherapies for prostate cancer, many groups are exploring vaccination strategies to induce an immune response against prostate specific antigen (PSA). To determine if T-cell recognition of PSA might be a feature of a naturally occurring human disease, we have studied patients with prostatitis, a poorly understood clinical syndrome of men in which there is evidence that an immune response directed against the prostate may be occurring. We wished to determine if a T-cell response to PSA might be occurring in these patients. We generated long-term T-cell lines from peripheral blood mononuclear cells (PBMC) of one patient with granulomatous prostatitis using purified PSA as an antigen. Several CD4+ and CD8+ TcR alpha/beta+ T-cell lines were selected for PSA reactivity as measured by at least a threefold increase in IFN-gamma secretion in response to PSA presented by irradiated autologous PBMC. CD4 and CD8 T-cell lines recognized PSA in the context of HLA-DRbeta1*1501 and HLA-B*0702, respectively. The specificity and HLA restriction of the lines was confirmed using EBV-B cell lines infected with a recombinant PSA-expressing vaccinia virus and also engineered to express PSA by retroviral transfection. HLA-matched targets infected by control vector as well as HLA-mismatched PSA-expressing targets did not induce the response. The data demonstrate that PSA-specific T cells are present in the PBMC of this patient with granulomatous prostatitis, who may be manifesting naturally the type of immune response directed at the prostate that is the goal of prostate cancer immunotherapy. However, the Class I-restricted epitope has not yet been demonstrated to be expressed on the surface of prostate cancer cells. To our knowledge, this is the first demonstration of HLA-DRB1*1501- or HLA-B*0702-restricted responses to PSA and extends the number of HLA molecules accommodating the use of PSA antigen as a candidate vaccine for prostate cancer immunotherapy.

Human macrophages, but not dendritic cells, are activated and produce alpha/beta interferons in response to Mopeia virus infection

Lassa virus (LV) and Mopeia virus (MV) are closely related members of the Arenavirus genus, sharing 75% amino acid sequence identity. However, LV causes hemorrhagic fever in humans and nonhuman primates, whereas MV cannot induce disease. We have previously shown that antigen-presenting cells (APC)-macrophages (MP) and dendritic cells (DC)-sustain high replication rates of LV but are not activated, suggesting that they play a role in the immunosuppression observed in severe cases of Lassa fever. Here, we infected human APC with MV and analyzed the cellular responses induced. MV infection was productive in MP and even more so in DC. Apoptosis was not induced in either cell type. Moreover, unlike DC, MP were early and strongly activated in response to MV, as shown by the increased surface expression of CD86, CD80, CD54, CD40, and HLA-abc and by the production of mRNA encoding alpha interferon (IFN-alpha), IFN-beta, tumor necrosis factor alpha and interleukin-6. In addition, MV-infected MP produced less of the virus than DC, which was related to the fact that these cells secreted IFN-alpha. Thus, the strong activation of MP is probably a major event in the control of MV infection and may be involved in the induction of an adaptive immune response in infected hosts. These results may explain the difference in pathogenicity between LV and MV.

Preferential HLA usage in the influenza virus-specific CTL response

To study whether individual HLA class I alleles are used preferentially or equally in human virus-specific CTL responses, the contribution of individual HLA-A and -B alleles to the human influenza virus-specific CTL response was investigated. To this end, PBMC were obtained from three groups of HLA-A and -B identical blood donors and stimulated with influenza virus. In the virus-specific CD8(+) T cell population, the proportion of IFN-gamma- and TNF-alpha-producing cells, restricted by individual HLA-A and -B alleles, was determined using virus-infected C1R cells expressing a single HLA-A or -B allele for restimulation of these cells. In HLA-B*2705- and HLA-B*3501-positive individuals, these alleles were preferentially used in the influenza A virus-specific CTL response, while the contribution of HLA-B*0801 and HLA-A*0101 was minor in these donors. The magnitude of the HLA-B*0801-restricted response was even lower in the presence of HLA-B*2705. C1R cells expressing HLA-B*2705, HLA-A*0101, or HLA-A*0201 were preferentially lysed by virus-specific CD8(+) T cells. In contrast, the CTL response to influenza B virus was mainly directed toward HLA-B*0801-restricted epitopes. Thus, the preferential use of HLA alleles depended on the virus studied.

HLA-A and -B phenotypes associated with tuberculosis in population from north-eastern Romania

HLA antigens are involved in inducing either susceptibility or resistance to different diseases. Many studies reported various associations between HLA antigens and tuberculosis, depending on race, ethnic group and geographic area.

AIM

Our purpose was to identify HLA class I antigens inducing susceptibility to tuberculosis in population from North-Eastern Romania.

PATIENTS AND METHODS

The study group consisted of 50 tuberculosis patients and the control group included 90 healthy people. HLA-A and HLA-B antigens were determined using the CDC-NIH (complement-dependent-cytotoxicity-National Institute of Health) assay. A comparison was made between the frequency of HLA antigens expression in the two studied groups.

RESULTS

HLA-B18 and HLA-A29(19) were expressed more frequently in tuberculosis patients. The difference was statistically significant only for HLA-B18 antigen. HLA-B7 and -B61(40) antigens were expressed with statistically significant higher frequency in controls compared to tuberculosis patients. The frequency of other HLA-A and HLA-B antigens was either comparable in the two groups or without statistical significance. CONCLUSIONS We found a positive association between HLA-B18 antigen and tuberculosis, while HLA-B7 and HLA-B61(40) antigens seem to protect against the disease.

[Human leukocyte antigen--B/C transcription in oral squamous cell carcinomas]

OBJECTIVE

The aim of this study was to investigate the mRNA expression levels of human leukocyte antigen Class I at different progressive stages of human oral squamous cell carcinomas.

METHODS

The expression of mRNA of human leukocyte antigen--B/C was detected in 23 primary tumors, 10 metastatic focuses and 11 histological normal oral epithelia using in situ hybridization method with a digoxigenin--labeled DNA probe. The probe was human leukocyte antigen--B/C locus specific.

RESULTS

The hybridization signals were present in the cytoplasm of either normal epithelia or tumor cells. The integrated optical density values of the hybridization signals were detected with the aid of an image analysis system. The results showed that the average integrated optical density values of the primary tumors were statistically lower than the normal oral epithelia (P < 0.05), but there was no significant difference between metastatic tumors and the primary tumors or the normal epithelia. The integrated optical density values measured in the metastatic tumors also did not show statistically differences compared with the primary tumors of the same patients.

CONCLUSION

Impaired regulation of human leukocyte antigen--B/C transcription could occur but might not be directly associated with metastasis of oral squamous cell carcinomas.

Down-regulation of HLA-A expression correlates with a better prognosis in colorectal cancer patients

To evaluate the prognostic impact of human leukocyte antigen class I (HLA-I) expression on immune surveillance in colorectal cancer, we studied 88 curatively resected tumors for HLA-A and HLA-B/C expression and correlated these data to clinical and histopathological parameters. HLA-A was normal (all tumor cells had HLA expression) in 32%, reduced (HLA-negative and -positive tumor cells coexisted) in 56%, or absent (no tumor cells expressed HLA) in 12% of evaluable cases. HLA-B/C was normal in 47%, reduced in 47%, and absent in 7% of the cases. Considering both markers, total HLA-I expression was normal in 27%, reduced in 63%, absent in 7%, and could not be evaluated in 3% of the cases due to absent HLA-A expression in tumor and normal cells. Down-regulation of HLA-A expression significantly correlated with a lower tumor stage (p = 0.005), mucinous tumors (p = 0.05), a lower incidence of recurrences (p = 0.03), and a longer disease-free survival (p = 0.02). Down-regulation of HLA-B/C expression correlated with a lower tumor stage (p < 0.001) and a longer disease-free survival (p = 0.04). In multivariate analysis, HLA-A down-regulation was the only prognostic factor correlated with a longer disease-free survival (p = 0.02). Six tumors were negative for HLA-A and -B/C and did not recur during follow-up. Therefore, we analyzed microsatellite instability (MSI) in these cases. Three of these six tumors indeed showed down-regulation of MLH-1, MSH-2, or MSH-6, indicating a MSI-high phenotype. Beta-2-microglobulin protein expression was lost in five of six of the HLA-I-negative cases, but frame shift mutations in three repetitive sequences in beta2-microglobulin were absent. In contrast, loss of MLH-1, MSH-2, and MSH-6-protein expression was only observed in two of nine matched controls with reduced or normal HLA-A and -B/C expression. Our data showed that HLA-I was down-regulated in 72% of colorectal cancers and provided independent prognostic information for a longer disease-free survival. The better prognosis may be caused by elimination of HLA-negative cells by natural killer cells or by an attenuated tumor aggressiveness, as is seen in tumors with a MSI-high phenotype.

Integrated functional genomics approach for the design of patient-individual antitumor vaccines

Our aim is to identify as many candidates as possible for tumor-associated T-cell epitopes in individual patients. First, we performed expression profiling of tumor and normal tissue to identify genes exclusively expressed or overexpressed in the tumor sample. Then, using mass spectrometry, we characterized up to 77 different MHC ligands from the same tumor sample. Several of the MHC ligands were derived from overexpressed gene products, one was derived from a proto-oncogene, and another was derived from a frameshift mutation. At least one was identified as an actual T-cell epitope. Thus, we could show that by combining these two analytic tools, it is possible to propose several candidates for peptide-based immunotherapy. We envision the use of this novel integrated functional genomics approach for the design of antitumor vaccines tailored to suit the needs of each patient.

[Influence of HLA class I molecules expression on tumor cell resistance to NK lysis and the IFN-gamma regulatory effect]

OBJECTIVE

To investigate the relation between the NK lysis and HLA molecules expressed on the target cells as well as the regulatory effect of IFN-gamma.

METHODS

The level of HLA-ABC molecules on seven human tumor cell lines were detected through the indirect immune fluorescence stain. NK lysis changes were observed after the blocking of HLA molecules on the target cells with the anti-HLA monoclonal antibodies or treating target cells with IFN-gamma.

RESULTS

1. Most of the tumor cell lines showed a complete or partial loss of HLA-ABC molecules, 2. After the HLA molecules had been marked on the target cells with the anti-HLA-ABC antibodies, the tumor cell susceptibility to the lysis of NK cells attack increased significantly and 3. After having being treated with IFN-gamma 500 U/ml for more than 48 hours, the HLA-ABC molecule levels on K562, M21 and PG cells went up. At the same time, their susceptibility to NK lysis was reduced. However, the resistance to Karpas, HL60 and HT29 NK lysis demonstrated a noticeable increase. The IFN-gamma promoted the apoptosis of HL60 and HT29 cells.

CONCLUSION

The NK cells are capable of recognizing the HLA molecules on the target cells and show no lysis in providing a negative signal with the KIRs, an effect which the anti-HLA monoclonal antibodies are able to eliminate. IFN-gamma can be applied to make up for the loss of HLA molecules on some of the tumor cells, it can also facilitate some of the tumor cells' apoptosis.

Differences in the expression of human class I MHC alleles and their associated peptides in the presence of proteasome inhibitors

We have studied the contributions of proteasome inhibitor-sensitive and -insensitive proteases to the generation of class I MHC-associated peptides. The cell surface expression of 13 different human class I MHC alleles was inhibited by as much as 90% or as little as 40% when cells were incubated with saturating concentrations of three different proteasome inhibitors. Inhibitor-resistant class I MHC expression was not due to TAP-independent expression or preexisting internal stores of peptides. Furthermore, it did not correlate with the amount or specificity of residual proteasome activity as determined in in vitro proteolysis assays and was not augmented by simultaneous incubation with multiple inhibitors. Mass spectrometry was used to directly characterize the peptides expressed in the presence and absence of proteasome inhibitors. The number of peptide species detected correlated with the levels of class I detected by flow cytometry. Thus, for many alleles, a significant proportion of associated peptide species continue to be generated in the presence of saturating levels of proteasome inhibitors. Comparison of the peptide-binding motifs of inhibitor-sensitive and -resistant class I alleles further suggested that inhibitor-resistant proteolytic activities display a wide diversity of cleavage specificities, including a trypsin-like activity. Sequence analysis demonstrated that inhibitor-resistant peptides contain diverse carboxyl termini and are derived from protein substrates dispersed throughout the cell. The possible contributions of inhibitor-resistant proteasome activities and nonproteasomal proteases residing in the cytosol to the peptide profiles associated with many class I MHC alleles are discussed.

HLA-A and HLA-B transcription decrease with ageing in peripheral blood leucocytes

Immunosenescence involves modifications of humoral and cellular immunity. In a previous study, we have shown a locus-dependent reduction of HLA class-I cell surface expression on peripheral lymphocytes and monocytes with advancing age. Here we report the quantitative analysis of HLA-A and -B transcripts from PBL of 54 healthy subjects aged 21-90 years. Using a competitive RT-PCR method, we observed a significant decrease of HLA-A (P < 0.0001) and -B (P = 0.0025) mRNA contents with increasing age. Secondly, to investigate this locus-dependent alteration of HLA class-I transcription, we performed EMSA using nuclear extracts from PBL of five young (24-31-year-old) and 5 elderly (58-69 years old) donors with locus A and B sequences of the Enh-A as probes. No qualitative variation of EMSA profiles appeared between the two groups of donors with 6 and 4 bandshift for the locus A and B, respectively. Quantitatively, we observed a significant increase of B4 intensity in the elderly group compared to the young group (P < 0.05). These results suggest that the variation of DNA binding protein could contribute to the lower transcription of HLA-A and -B with ageing. These alterations of HLA class-I expression at the transcriptional level could lead to the unresponsiveness of CD8 T cells due to default of antigen presentation with ageing.

Non-expression of HLA-B*5111N is caused by an insertion into the cytosine island at exon 4 creating a frameshift stop codon

The identification of the "blank" allele HLA-B*5111N, which was detected in German and Czech individuals, is described. In the pedigree analysis this new allele segregates with the serological haplotype HLA-A2; B-; DR4 which is frequent in Czech population. The non-expression of B*5111N is caused by the insertion of an additional cytosine molecule at the cytosine island between the nucleotides 621-626 (codons 183-185, first three codons of exon 4) leading to a frame shift that creates a stop codon at codon 196. This insertion may be explained either by conversion with the pseudogene HLA-J or by slipped-strand mispairing. In order not to overlook the presence of alleles with altered expression in case of hematopoietic stem cell transplantation, both serological and DNA-based typing should be performed (Note).

Unbalanced expression of HLA-A and -B antigens: a specific feature of cutaneous melanoma and other non-hemopoietic malignancies reverted by IFN-gamma

Conflicting evidences suggested that levels of HLA-A and -B antigens expressed on normal and neoplastic cells of given individuals are genetically predetermined, or, on the other hand, regulated by molecular mechanisms generating the down-regulated expression of HLA-B antigens frequently observed on melanoma cells. In our study, we quantitated, both at the protein and mRNA level, the amounts of HLA-A and -B antigens constitutively expressed on 23 primary cultures of metastatic melanomas and on autologous peripheral blood mononuclear cells (PBMC). Flow cytometric analyses identified a significantly (p < 0.01) lower expression of HLA-B antigens on melanoma cell cultures but not on autologous PBMC. Consistently, lower amounts of HLA-B antigens mRNA were detected by RNase protection assay exclusively in neoplastic cells. This unbalanced expression of HLA-A and -B antigens was readily reverted by interferon (IFN)-gamma but not by the DNA hypomethylating agent 5-aza-2'-deoxycytidine in 4 melanoma cell cultures investigated. Significantly (p < 0.05) lower levels of HLA-B antigens were also detected on cells from solid malignancies of different histotypes but not on neoplastic cells from hemopoietic neoplasms; levels of HLA-B antigens were rapidly up-regulated by IFN-gamma exclusively on non-hemopoietic transformed cells. Together, these data strongly argue against a genetic predetermination of the amounts of HLA-A and -B antigens expressed on normal and neoplastic cells of distinct melanoma patients and suggest that constitutively low levels of HLA-B antigens are a specific feature of non-hemopoietic transformed cells that is controlled by common regulatory mechanism(s) and that is possibly shared by non-hemopoietic normal cells.

HLA-G1 co-expression boosts the HLA class I-mediated NK lysis inhibition

It is now acknowledged that the pattern of HLA-G expression is not restricted to extravillous cytotrophoblast cells, as several studies described HLA-G in HLA class I+ cells, such as thymic epithelial cells, cytokine-activated monocytes and some tumors. In these situations, HLA-G may provide an additional inhibitory signal to escape from NK cell-mediated cytotoxicity. Accordingly, the aim of this study was to define the behavior of HLA-G once it is co-expressed into an HLA-A, -B, -C and -E+ cell line. For this purpose, HLA-G1 cDNA was transfected into an HLA class I+ melanoma cell line which was used as a target towards freshly isolated peripheral blood NK cells. Cytotoxic experiments using either anti-HLA-G1 or anti-HLA-G1 inhibitory receptor mAb show that HLA-G1 boosts the HLA class I-mediated inhibition of polyclonal NK cells through interaction with ILT-2, which appears as the major HLA-G1 inhibitory receptor involved. Nevertheless, HLA-G1 is also able to inhibit the cytolytic activity of an ILT-2- NK clone which otherwise expresses another HLA-G1 inhibitory receptor belonging to the KIR103 gene family. In order to more precisely define the relative role exerted by HLA-G1 versus -E on polyclonal NK cells, antibody-blocking assays were carried out using either anti-HLA class I or anti-CD94/NKG2A. Results demonstrate that in the absence of HLA-G1, the naturally expressed HLA class I-mediated NK inhibition is predominantly exerted by HLA-E through binding with CD94/NKG2A. In contrast, once HLA-G1 is expressed, it becomes the major NK inhibitory ligand.

Mechanisms for genetically predetermined differential quantitative expression of HLA-A and -B antigens

Previous studies showed that different HLA-A and -B antigens are differentially expressed in cells. Their relative quantities are genetically predetermined and inherited according to Mendelian laws. To investigate mechanisms responsible for this differential expression, a correlation study between the relative quantities of different HLA-A and -B proteins and their mRNA levels in eight different HLA-phenotyped lymphoblastoid cell lines (LCLs) were performed. The results show proportional correlation in all the studied cell lines except those that are positive for HLA-A24. Study of the turnover of HLA antigens reveals that different HLA-A and -B antigens are proportionally degraded. Measurement of the relative quantities of HLA-A and -B mRNAs in six LCLs before and after treatment with 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB), an inhibitor of RNA polymerase II, demonstrates that HLA-A and -B mRNAs are proportionally degraded except slight differences in two LCLs. Measurement of the relative quantities of different HLA-A and -B pre-mRNAs in nuclei shows that they are not proportional to the relative quantities of their respective mature mRNAs in cytoplasm in four of six LCLs. These results indicate that combinations of different regulatory steps which include gene transcription, pre-mRNA splicing and mRNA degradation are involved in the genetically predetermined quantitative differential expression of HLA-A and -B antigens. Transcription of HLA genes and splicing of HLA pre-mRNAs appear to be the dominant regulatory steps.

Differential expression of human major histocompatibility class I loci: HLA-A, -B, and -C

Expression of the human class I MHC loci, HLA-A, -B, and -C, was examined by reverse transcription and competitive PCR with locus-specific primers. This approach allows unambiguous identification of target sequences by analysis of the amplified products. JY and Pala lymphoblastoid B cells express more HLA-A than HLA-B mRNAs and little HLA-C mRNA. Raji Burkitt lymphoma and HeLa carcinoma cells express approximately equal amounts of HLA-A and HLA-C mRNAs but less HLA-B mRNA. Jar trophoblast cells express no HLA class I mRNAs. Surprisingly, K562 leukemia cells express significant amounts of HLA-C mRNA. However, K562 cells contain no detectable HLA-A or -B mRNAs, suggesting that these loci are regulated independently. Furthermore, cultured endothelial cells and smooth muscle cells express low, approximately equal amounts of HLA-A, -B, and -C mRNAs, whereas donor-matched, EBV transformed B cells express much more HLA-B mRNA, suggesting that cell type dependent regulation underlies differential locus expression. Finally, expression of HLA class I molecules on the cell surface correlates with total HLA mRNAs but not with mRNAs encoded by any one locus. Differential expression of these HLA class I loci may contribute to cell-type dependent immune reactions by preferentially presenting distinct peptides to T cells.

Distinct functions of tapasin revealed by polymorphism in MHC class I peptide loading

Peptide assembly with class I molecules is orchestrated by multiple chaperones including tapasin, which bridges class I molecules with the TAP and is critical for efficient Ag presentation. In this paper, we show that, although constitutive levels of endogenous murine tapasin apparently are sufficient to form stable and long-lived complexes between the human HLA-B*4402 (B*4402) and mouse TAP proteins, this does not result in normal peptide loading and surface expression of B*4402 molecules on mouse APC. However, increased expression of murine tapasin, but not of the human TAP proteins, does restore normal cell surface expression of B*4402 and efficient presentation of viral Ags to CTL. High levels of soluble murine tapasin, which do not bridge TAP and class I molecules, still restore normal surface expression of B*4402 in the tapasin-deficient human cell line 721.220. These findings indicate distinct roles for tapasin in class I peptide loading. First, tapasin-mediated bridging of TAP-class I complexes, which despite being conserved across the human-mouse species barrier, is not necessarily sufficient for peptide loading. Second, tapasin mediates a function which probably involves stabilization of empty class I molecules and which is sensitive to structural compatibility of components within the loading complex. These discrete functions of tapasin predict limitations to the study of HLA molecules across some polymorphic and species barriers.

Biosynthesis of HLA-C heavy chains in melanoma cells with multiple defects in the expression of HLA-A, -B, -C molecules

Recent investigations have shown that malignant transformation may down-regulate the expression of class I HLA molecules, beta2-microglobulin (beta2m) and members of the antigen-processing machinery. In the present study, we HLA-genotyped and identified at a biochemical level the three (HLA-A25, -B8, -Cw7) class I alleles expressed by the previously described [D'Urso CM et al (1992) J Clin Invest 87: 284-292] beta2m-defective human melanoma FO-1 cell line and tested their ability to interact with calnexin, calreticulin and the TAP (transporter associated with antigen processing) complex. All these alleles were found to bind calnexin, but not calreticulin or the poorly expressed TAP complex, both in parental and beta2m-transfected FO-1 cells, demonstrating a complex defect of class I expression in FO-1 cells. In these conditions, Cw7 heavy chains interacted with calnexin more strongly than A25 and B8, and preferentially accumulated in the endoplasmic reticulum, in both a calnexin-associated and a calnexin-free form. In addition, they could be transported to the cell surface at low levels even in the absence of beta2m, without undergoing terminal glycosylation. These results establish a parallel between HLA-C and the murine Db and Ld molecules which have been found to be surface expressed and functional in beta2m-defective cells. They also demonstrate distinctive features of HLA-C molecules. We propose that the accumulation of several assembly intermediates of HLA-C might favour the binding of peptide antigens not readily bound by HLA-A and -B molecules in neoplastic cells with suboptimal class I expression.

Is the expression of classical HLA class I antigens on trophoblast of importance for human pregnancy?

PROBLEM

Human leukocyte antigen (HLA)-C and possibly also HLA-B seem to be expressed on the extravillous trophoblast. These antigens carry epitopes that function as ligands for natural killer (NK)-cell-inhibitory receptors. Antitrophoblast cytotoxicity mediated by decidual NK cells might be involved in miscarriage. We thus found it relevant to elucidate whether parental HLA-C and -Bw polymorphism play a role in recurrent miscarriage (RM).

METHOD OF STUDY

HLA-C and -Bw investigations by DNA-based techniques were undertaken in 35 couples with unexplained RM and in 30 couples with normal fecundity. The number of HLA-C- and -Bw-related supertypic specificities that can bind NK-cell-inhibitory receptors was evaluated in selected couples.

RESULTS

The proportions of couples with RM and control couples carrying four HLA-C alleles with the same NK-cell-inhibitory supertypic specificities were equal. In 46% of studied couples with RM, all four HLA-B alleles carried the HLA-Bw6 supertypic specificity, which was significantly higher than the corresponding frequency (17%) in the control couples (P < 0.02).

CONCLUSIONS

The expression of polymorphic HLA-C on trophoblasts does not seem to play a role in RM. Assuming that HLA-B is expressed on trophoblasts, we may suggest that the revealed predominance of HLA-Bw6 expression (which excludes the presence of HLA-Bw4-protective antigens) may predispose a particular couple to the RM phenomenon.

Absence of imprinting of HLA class Ia genes leads to co-expression of biparental alleles on term human trophoblast cells upon IFN-gamma induction

Human trophoblast cells have developed various efficient regulatory mechanisms to prevent cell surface expression of the classical HLA-A, -B, and (but not always) -C class I molecules. This allows them to escape maternal alloimmune attack during pregnancy. However, recent results have demonstrated that such a lack of expression could be reversed in villous cytotrophoblast cells purified from term placenta by in vitro IFN-gamma treatment. In this context, we investigated whether both maternal and paternal HLA class Ia antigens were co-dominantly expressed in such trophoblast cells. Using polymerase chain reaction sequence-specific primers for HLA-A and HLA-C alleles, we detected transcripts of both paternal and maternal origins, showing that these genes were not affected by genomic imprinting, at least in term placenta. After in vitro IFN-gamma treatment, the polymorphic HLA-A and HLA-B antigens of both parental origins become detectable at the cell surface, as assessed by flow cytometry and/or complement-dependent microtoxicity test. Appearance of paternal antigens on trophoblast cells upon IFN-gamma induction raises the question of the in vivo biological consequences of this phenomena, in term of materno-fetal tolerance and in particular of a potential allogeneic cytotoxic immune response.

[Presence of alternatively spliced messenger RNA for HLA-A, -B and -C in platelets]

Recently we demonstrated that platelets contain specific messenger RNA (mRNA) encoding for the transmembrane HLA class I molecule (44 kDa). In this study we analyzed lymphocytes as well as platelets for the presence of alternatively spliced mRNA with deleted transmembrane domain resulting in soluble HLA class I antigens (39 kDa). PCR amplification of lymphocyte RNA led to a product specific for alternatively spliced cDNA corresponding to the presence of soluble HLA in plasma, while this product could not be obtained from platelet mRNA. These results suggest that platelets in contrast to lymphocytes are unable to synthesize soluble HLA antigens via alternative splicing.

NK cells from human MHC class I (HLA-B) transgenic mice do not mediate hybrid resistance killing against parental nontransgenic cells

We have investigated the capacity of human MHC class I HLA-B gene products, HLA-B27, -B7 (fully human), and -B7kb (human-mouse hybrid consisting of the alpha1 and alpha2 domains of HLA-B7, and the alpha3 and cytoplasmic domains of mouse H-2Kb), expressed on mouse NK cells during ontogeny to influence NK recognition of otherwise syngeneic mouse target cells. Despite a high level of surface expression of the transgene (comparable to that of endogeneous H-2DbKb molecules), the direct killing of YAC-1 targets, and the killing of P815 targets in a redirected lysis assay, the NK effectors of these transgenic mice could not mediate hybrid resistance-like killing of nontransgenic C57BL/6 target cells either in vitro or in vivo. Splenocytes from B6-B27 mice could be used to generate CTL lines against a B27-binding peptide, implying that T cells restricted by HLA-B27 developed during ontogeny. NK cells from B6-B27 could lyse B6-B27 Con A lymphoblasts pulsed with Db-binding peptide but not B27-binding peptides. Taken together, our results show that these human HLA-B transgene products cannot function as class I MHC "self" elements for mouse NK cells, even when present throughout ontogeny.

Nicotinamide decreases cytokine-induced activation of orbital fibroblasts from patients with thyroid-associated ophthalmopathy

We used flow cytometry to investigate the effects of nicotinamide, an inhibitor of poly (ADP ribose) synthetase, on the cell-surface expression of cytokine-induced human leukocyte antigen (HLA)-A,B,C antigen, HLA-DR antigen, intercellular adhesion molecule 1, CD44, and Fas expression in cultured orbital fibroblasts from patients with thyroid-associated ophthalmopathy. After two to seven passages, cultured orbital fibroblasts were incubated for 3 days with interferon gamma or tumor necrosis factor alpha in the presence of nicotinamide. Nicotinamide inhibited the induction of both HLA-DR and intercellular adhesion molecule 1 expression by cytokines on fibroblasts but did not interfere with induction of HLA-A,B,C, or CD44 expression. Nicotinamide also inhibited the proliferation of orbital fibroblasts, as assessed by a [3H]-thymidine incorporation assay and cell counts. Nicotinamide also enhanced the expression of the apoptosis-mediating protein Fas on fibroblasts. Our data suggest that nicotinamide inhibits cytokine-induced activation of fibroblasts and thus may decrease the autoimmune injury to the orbit in thyroid-associated ophthalmopathy.

Hierarchy of Epstein-Barr virus-specific cytotoxic T-cell responses in individuals carrying different subtypes of an HLA allele: implications for epitope-based antiviral vaccines

Major histocompatibility complex class I-restricted Epstein-Barr virus (EBV)-specific cytotoxic T lymphocytes (CTLs) in healthy virus carriers constitute a primary effector arm of the immune system in controlling the proliferation of virus-infected B cells in vivo. These CTLs generally recognize target epitopes included within the latent antigens of the virus. For example, CTLs from HLA B44+ healthy virus carriers often recognize peptide EENLLDFVRF [corrected] from EBV nuclear antigen 6. However, the strength of this response directly correlates with the HLA B44 subtype expressed by the individual donor. Indeed, HLA B*4405+ virus carriers consistently show a very high frequency of CTL precursors for the EENLLDFVRF [corrected] epitope, while a much weaker response is seen in HLA B*4403+ and HLA B*4402+ individuals. This disparity is not due to an intrinsic difference in the CTLs generated by individuals carrying different subtypes of HLA B44. In fact, virus-specific CTLs recognize EENLLDFVRF [corrected] peptide-sensitized HLA B*4405+ target cells more efficiently than B*4402+ or B*4403+ target cells irrespective of the HLA B44 subtype expressed by the donors from whom these effectors were isolated. This effect is evident whether the CTL epitope is endogenously processed or exogenously presented. In addition, a comparison of the intracellular transport kinetics of different B44 subtypes revealed that the B*4405 allele is rapidly assembled and arrives in the trans-Golgi compartment at a faster rate than B*4402 or B*4403. Based on these results, we propose that HLA class I alleles that are capable of binding peptides more efficiently from the intracellular pool, and are rapidly assembled and transported, may confer a protective advantage against viral infection.

Regulation of human monocyte apoptosis by the CD14 molecule

Bacterial products such as LPS have been shown to activate monocytes and to increase CD14 expression, while anti-inflammatory cytokines, i.e., IL-4, down-regulate CD14. Furthermore, activation of monocytes increases survival, whereas deactivation evokes apoptosis (programmed cell death, PCD). This correlation among activation, CD14 expression, and the lifespan of the cells prompted us to investigate the role of CD14 in monocyte apoptosis. The effects of LPS and IL-4 on the expression of CD14, indicated by binding of Leu M3 Ab, and PCD of monocytes were studied simultaneously and in a kinetic fashion by multiparameter flow cytometry. Monocyte PCD was determined by binding of FITC-conjugated annexin V, which indicates apoptotic cell death in early stages, and was confirmed using well-established detection methods, i.e., DNA electrophoresis, electron microscopy, or colorimetric DNA staining. The present study shows that the LPS-induced increase in CD14 expression rescued monocytes from apoptosis, whereas IL-4 treatment first down-regulated CD14 expression and consecutively evoked apoptosis. CD14-/annexin V- monocytes were not apoptotic as confirmed by DNA electrophoresis, whereas CD14-/ annexin V+ monocytes showed clear apoptotic features. Kinetic studies ruled out that monocytes first bound annexin V and later lost the CD14 Ag. Other molecules, such as HLA-A, -B, and -C Ags, were not down-regulated during apoptosis. Enzymatic removal of membrane-bound CD14 by phosphatidylinositol-specific phospholipase C evoked PCD similarly to IL-4. These results suggest that regulation of CD14 receptor expression is an early effector mechanism mediating life or death of monocytes. Down-regulation or removal of the receptor triggers apoptosis, whereas up-regulation promotes survival.

HLA phenotypes in healthy aged subjects

One hundred and seventy-one unrelated elderly healthy subjects selected according to the Senieur protocol (57 men and 114 women), aged 75-104 years, and 405 healthy individuals (238 men and 167 women), aged 18-65 years, were typed for HLA-A, HLA-B, and HLA-DR antigens. The purpose of the study was to investigate a possible association between HLA antigens and longevity. In the total group of elderly, an increased frequency of HLA-B16 (11.11 vs. 5.43%) and HLA-DR7 (38.33 vs. 15.67%) and a decreased frequency of HLA-B15 (1.75 vs. 5.18%) and HLA-DR4 (11.66 vs. 24.15%) were observed. The HLA-B15DR4 haplotype was not represented (vs. 2.1%), HLA-A1B8 was found with a low frequency (2.9 vs. 4.4%), and HLA-B8DR3 was very rarely found (1.6 vs. 10.1%), whereas the HLA-B13DR7 haplotype was observed with an increased frequency (6.6 vs. 3.3%). These results are in agreement with other published data and suggest that longevity in humans may be influenced by the genetic background.

Role of HLA-B*5101 binding nonamer peptides in formation of the HLA-Bw4 public epitope

HLA-Bw4 is one of two HLA-B public epitopes which are discriminated by specific alloantisera and mAb. It is believed that the 77-83 of HLA-B molecules form the Bw4 epitope recognized by specific antibodies. This epitope is also recognized by NKB1 receptors on NK cells. We investigated the role of a peptide bound to HLA-B molecules on the formation of the Bw4 epitope recognized by two HLA-Bw4-specific mAb, TU109 and TU48, which recognized the difference of the Bw4 epitope among HLA-B52, -B52 and -B53. Recognition of the HLA-B*5101-peptide complex by these mAb was examined using a panel of HLA-B*5101 binding nonamer peptides. The sequence of HLA-B*5101 binding peptides has a minimum influence on the binding of TU48 mAb to HLA-B*5101 molecules. In contrast, the binding of TU109 mAb to HLA-B*5101 molecules was critically influenced by the sequence of a peptide bound to HLA-B*5101 molecules. TU109 mAb did not recognize HLA-B*5101 binding peptides carrying small or negatively charged residues at P8. The results were confirmed by a panel of mutant peptides at P8. Taken together, these results indicate that a positively charged or neutralized side chain of P8 is critical for the epitope formation of Bw4 recognized by this mAb.

Kinetically coordinated induction of TAP1 and HLA class I by IFN-gamma: the rapid induction of TAP1 by IFN-gamma is mediated by Stat1 alpha

Transporter associated with Ag processing-1 (TAP1) is induced by IFN-gamma more rapidly than is HLA class I. Kinetic analysis of transfectants reveals that IFN-gamma activates the TAP1 promoter more rapidly than the HLA-B7 class I promoter. A gamma-activating sequence (GAS) in the TAP1 promoter is necessary for the rapid induction by IFN-gamma. Two overlapping IFN consensus sequences contribute to the constitutive and TNF-induced expression of TAP1 but are not necessary for the IFN-gamma response. Moreover, IFN-gamma activates the GAS-binding protein Stat1 alpha much more rapidly than it induces the IFN consensus sequence-binding protein IRF-1, which mediates the response of the HLA-B7 class I promoter. We conclude that IFN-gamma uses different transcription factors to regulate the sequence of appearance of these interacting gene products.

Selective loss of human leukocyte antigen class I allele expression in advanced renal cell carcinoma

The expression of human leukocyte antigen (HLA) class I alleles was analyzed in 65 renal cell carcinomas using one-dimensional isoelectric focusing. Normal organ tissue and peripheral blood lymphocytes were used as controls. The patients were serologically typed using the standard microcytotoxicity test. Forty-two patients were staged as pT1 or pT2, and 23 patients had advanced tumor stages (pT3/pT4). In all cases the HLA-A,B phenotypes were confirmed using one-dimensional isoelectric focusing. The expression of HLA expression was reduced in two tumors [1 x HLA-A1(pT2); 1 x HLA-A28 (pT2)]. In three carcinomas the expression of HLA-A1 was lost. One tumor showed a combined loss of HLA-A2 and HLA-B38. These selective losses occurred in tumor stage pT3 (n = 1) or pT4 (n = 3; P = 0.013, Fisher's exact test). This leads to the conclusion that the loss of HLA expression is predominantly present in advanced tumor stages.

Low HLA-C expression at cell surfaces correlates with increased turnover of heavy chain mRNA

In comparison with HLA-A and -B, the protein products of the HLA-C locus are poorly characterized, in part because of their low level of expression at the cell surface. Here, we examine how protein-protein interactions during assembly and regulation of the mRNA level affect cell surface expression of HLA-C. We find that intrinsic properties of the HLA-C heavy chain proteins do not correlate with low cell surface expression: HLA-C heavy chains associate and dissociate with beta 2-microglobulin (beta 2m) at rates comparable to those found for HLA-A and -B, and increased competition for beta 2m does not alter the surface expression of HLA-C. From studies of chimeric genes spliced from the HLA-B7 and -Cw3 genes, we find that chimeric proteins containing the B7 peptide-binding groove can have low cell surface expression, suggesting that inefficiency in binding peptides is not the cause of low cell surface expression for HLA-C. The surface levels of HLA-A, -B, or -C in cells transfected with cDNA can be similar, implicating noncoding regions of HLA-C heavy chain genes in the regulation of surface expression. We find that HLA-C mRNA is expressed at lower levels than HLA-B mRNA and that this difference results from faster degradation of the HLA-C message. Experiments examining chimeric B7/Cw3 and B7/Cw6 genes suggest that a region determining low expression of HLA-C is to be found between the 3' end of exon 3 and a site in the 3' untranslated region, approximately 600 bases downstream of the translation stop codon.

Hepatitis C virus (HCV) genotype, tissue HCV antigens, hepatocellular expression of HLA-A,B,C, and intercellular adhesion-1 molecules. Clues to pathogenesis of hepatocellular damage and response to interferon treatment in patients with chronic hepatitis C

To obtain information on the mechanisms of hepatocellular damage and the determinants of response to interferon, hepatitis C virus (HCV) genotype, tissue HCV antigens, hepatocellular expression of HLA-A,B,C and intercellular adhesion-1 molecules, and the number of lobular T lymphocytes were studied in 38 anti-HCV-positive patients. 14 patients did not show a primary response to interferon treatment. HCV genotype 1b was detected in 11 of them. They displayed higher scores of HCV-positive hepatocytes, HLA-A,B,C, and ICAM-1 molecules expression than with the responders. HCV-infected hepatocytes maintained the capacity to express HLA-A,B,C and ICAM-1 molecules. CD8-positive T cells in contact with infected hepatocytes and Councilman-like bodies were observed. A significant correlation was found between the number of lobular CD8-positive T cells and alanine amino transferase levels. No differences were observed in clinical, biochemical, and histological features between patients with high and low number of hepatocytes containing HCV antigens. These data suggest a prominent role of T cell-mediated cytotoxicity in the genesis of hepatocellular damage. The high expression of interferon-inducible antigens like HLA-A,B,C molecules suggests the presence of strong activation of the interferon system possibly related to high HCV replication in nonresponder patients infected with genotype 1b.

Proportional amplification of individual HLA-A and -B antigens during upregulated expression of total class I HLA molecules

Our recent studies demonstrated that each specific HLA-A or -B antigen is not expressed in equal quantity in cells of an individual and that the relative amounts of different HLA-A and -B antigens are genetically predetermined following Mendelian laws. These findings suggest the potential genetic importance of varied quantitative HLA expression on target cells in determining the sensitivity to cytotoxic T lymphocytes. It would be important to know whether the amounts of different HLA antigens are differentially or proportionally amplified after upregulated expression of total HLA antigens. We have therefore determined the effects of IFN treatment, EBV transformation, and influenza virus infection on the quantitative expression of total HLA antigens and the relative quantities of different specific HLA-A and -B antigens in human fibroblasts cell line and peripheral blood mononuclear leukocytes. In contrast to earlier studies using the transfected HLA genes, our results show that different individual HLA-A and -B antigens are proportionally and not differentially amplified during upregulated expression of total class I HLA molecules. This finding indicates that the genetic predetermination of varied quantitative expression of HLA antigens may play a role in influencing antiviral immunity and disease susceptibility.

Lithocholic acid inhibits the expression of HLA class I genes in colon adenocarcinoma cells. Differential effect on HLA-A, -B and -C loci

Loss of HLA antigen expression is considered to be one of the mechanisms whereby tumor cells escape immune surveillance. We recently observed reduced or lost expression of HLA antigens during human colon carcinogenesis. We studied the effect of bile acids (BAs), long implicated in the pathogenesis of colon cancer, on the expression of HLA class I antigens in human colon adenocarcinoma cells. Lithocholic acid (LCA) decreased by 42% the expression of HLA class I antigens on the surface of these cells. This dose-dependent reduction was specific for both the target genes and the chemical structure of LCA, and was not evident in cultured liver cells. None of the other BAs that were tested manifested this effect. LCA, and to a lesser extent deoxycholic acid (DCA), decreased steady-state HLA class I mRNA levels. LCA decreased the rate of transcription of HLA-B (64%) and HLA-C (87%) but not HLA-A; DCA had a similar but less pronounced effect. In transient gene expression (CAT assays) experiments, we evaluated the role of a 0.6-0.7 kb EcoRI/XbaI sequence from the 5' flanking region of HLA-A2, -B7 and -Cw7 genes in the regulation of class I gene expression by LCA. LCA down-regulated by 70% the expression of the reporter gene for all three genes. We interpret these results as indicating a differential regulation of the three HLA loci by LCA. Our findings, demonstrating a profound effect of LCA on HLA class I gene regulation, raise the possibility that such a mechanism may be operative in vivo.

Transcriptional suppression of HLA-B expression by c-Myc is mediated through the core promoter elements

In melanoma, HLA class I expression is suppressed by overexpression of the c-myc oncogene. This suppression has severe consequences for the recognition of these tumor cells by the immune system of the organism. We show here that transcription of the HLA-B locus, which is mainly affected by c-Myc, is downmodulated at the level of initiation of transcription. The transcriptional activity of various HLA-B reporter constructs was tested in a melanoma cell line with low endogenous c-myc expression and in transfectants with high stable and transient c-myc expression. We demonstrated that the responsive region can be mapped to the core promoter region of HLA class I, ruling out any effects of c-myc overexpression on the enhancer A or enhancer B regions. The region subject to downregulation is confined to a 43 base pair fragment encompassing the CCAAT and TATA elements. By coupling this region to a heterologous viral enhancer, we showed that the downmodulation by c-Myc is independent of the presence and nature of an enhancer. These results suggest a mechanism in which c-Myc downregulates the expression of HLA class I genes by interfering with the basal level of transcription.

Generation of HLA-B55 restricted T lymphocyte mediated cytotoxicity against autologous LCL

The lymphocytes of one HLA-A11 positive individual (A1, A11, B49, B55) were stimulated in vitro with the autologous EBV transformed lymphoblastoid cell line (LCL). The culture contained HLA-A1, A11 and B55 restricted, LCL selective cytotoxic T cells (CTLs). In the T cell culture stimulated four times, the lysis of A11 and B55 carrying targets suggested that the subsets of the two latter CTL types had similar size. After further stimulations the B55 restricted CTLs were enriched in the culture. Earlier results suggested that in HLA-A11 positive individuals the A11-restricted LCL-selective CTL subset dominates. The sensitivity of a target panel including Burkitt lymphoma (BL) lines suggested that the peptide presented by the B55 molecule differs in A and B type EBV strain carrying cells.

Transcriptional regulation of HLA-A and -B: differential binding of members of the Rel and IRF families of transcription factors

HLA-A and -B transplantation antigens can be expressed differentially at the basal level and in response to interferons (IFNs). To determine which DNA control elements and nuclear factors are responsible for these differences, HLA-A and -B upstream regulatory regions were used in expression and mobility-shift analyses. The HLA-A enhancer was found to contain two Rel (KBF/NF-kappa B) binding motifs, while the HLA-B enhancer has only one and is transactivated less well by overexpression of the NF-kappa B p65 subunit. On the other hand, the HLA-B IFN response element mediates a much stronger induction by IFNs and has a higher affinity for IRF-1 and -2, which are transcription factors implicated in the regulation of major histocompatibility complex class I genes. These results suggest a molecular basis for the way in which HLA-A and -B loci have adapted to be differentially expressed and to respond to different sets of cytokine signals.

Quantitative expression of HLA class I molecules in acute non-lymphoblastic leukaemia cells

The present study concerns a panel of 33 acute non lymphoblastic leukaemia (ANLL) patients, previously typed for HLA-A,B serological specificities and including samples with a normal HLA-A,B phenotype (3,4 detected specificities) as well as samples with missing and extra specificities. Samples were analysed at the protein and/or RNA level in order to verify whether the observed typing anomalies were due to a modified quantitative expression of class I molecules. The number of HLA-A,B assigned specificities correlated significantly with the cell surface class I expression detected by indirect immunofluorescence using the monomorphic anti-class I MoAb W6/32 (Spearman rank correlation test, P < 0.01) and with the amount of class I Heavy Chain (HC, P < 0.05) and beta-2-microglobulin (beta 2m, P < 0.05) evaluated by Western blot in whole cell extracts. The RNA analysis suggested a HC-beta 2m coordinated down regulation at the mRNA level in a patient with no assigned HLA-A,B specificities. Another patient with no detectable HLA-A,B specificities showed a low expression selectively of the beta 2m protein. The results reported here demonstrate a heterogenous quantitative HLA class I expression in ANLL blasts, analogous to results reported for solid tumours.

Different rates of HLA class I molecule assembly which are determined by amino acid sequence in the alpha 2 domain

Assembly of HLA class I molecules was studied using pulse-chase labeling of B-lymphoblastoid cell lines with 35S-methionine, immunoprecipitation with antibodies detecting free or beta 2-microglobulin-associated heavy chain and isoelectric focusing. Marked differences between the products of different class I alleles were noted. HLA-B51 assembled very inefficiently, with considerable free heavy chain still detected in an unsialated form after a four hour chase. The closely related molecule HLA-B35 was in contrast rapidly assembled, all newly synthesized heavy chain being detected in a beta 2m-associated sialated form within 30 minutes. Analysis of naturally occurring variants related to HLA-B35 and HLA-B51 localized the region determining assembly efficiency to the alpha 2 domain, in which these molecules differ at eight amino acid residues. The effect was not due to a linked dominant gene, as both patterns of assembly were observed in a single cell line.