Association of the AChRalpha-subunit gene (CHRNA), DQA1*0101, and the DR3 haplotype in myasthenia gravis. Evidence for a three-gene disease model in a subgroup of patients

Myasthenia gravis (MG) is an autoimmune disease of the neuromuscular junction having multigene control. HLA-linked loci and the HB*14 micro-satellite marker located within the CHRNA gene which encodes the muscular acetylcholine receptor (AChR) alpha-subunit, the target self-antigen, were previously associated with MG. Combined analysis of these loci revealed a significant increase of DQA1*0101 alleles in HB*14+ vs. HB*14- patients and of DQA1*0501 alleles in HB*14/DQA1*0101 patients. Importantly, the effect of DQA1*0101 was independent of allelically associated DQB1 and DRB1 genes. In contrast, the effect of DQA1*0501 could not be dissociated from that of DRB1*03 and DQB1*0201 on the extended DR3 haplotype. These results indicate that a combination of three genes, of which two are linked to HLA, contributes to disease susceptibility in a subgroup of MG patients.

Measles virus nucleocapsid protein binds to FcgammaRII and inhibits human B cell antibody production

Despite the development of an efficient specific immune response during measles virus (MV) infection, an immunosuppression occurs contributing to secondary infections. To study the role of nucleocapsid protein (NP) in MV-induced immunosuppression, we produced recombinant MV NP. Purified recombinant NP exhibited biochemical, antigenic, and tridimensional structure similar to viral NP. By flow cytometry, we showed that viral or recombinant NP bound to human and murine B lymphocytes, but not to T lymphocytes. This binding was specific, independent of MHC class II expression, and dependent of the B lymphocyte activation state. The murine IIA1. 6 B cell line, deficient in the Fc receptor for IgG (FcgammaRII) expression, did not bind NP efficiently. Transfected IIA1.6 cells expressing either murine FcgammaRIIb1 or b2, or human FcgammaRIIa, b1*, or b2 isoforms efficiently bound NP. Furthermore, this binding was inhibited up to 90% by monoclonal antibodies 2.4G2 or KB61 specific for murine and human FcgammaRII, respectively. Finally, the in vitro Ig synthesis of CD40- or Ig-activated human B lymphocytes in the presence of interleukin (IL)-2 and IL-10 was reduced by 50% in the presence of recombinant NP. These data demonstrate that MV NP binds to human and murine FcgammaRII and inhibits in vitro antibody production, and therefore suggests a role for NP in MV-induced immunosuppression.

HLA class II DRB1, DQA1 and DQB1 polymorphisms in the Polish population from Wielkopolska

HLA DRB1, DQA1 and DQB1 alleles were determined by DNA PCR-SSO typing in a sample of 99 individuals originating from Wielkopolska (midwestern Poland). A high number of alleles (38 DRB1, 8 DQA1 and 14 DQB1) was detected at each locus, many of them presenting notable frequencies in this population. The three HLA loci are thus characterized by very high heterozygosity levels (93% for DRB1, 85% for DQA1, and 88% for DQB1), which confirms the results found for other European populations. A total of 6 DRB1-DQA1-DQB1 haplotypes are detected with an estimated frequency higher than 5%, namely, DRB1*1501-DQA1*0102-DQB1*0602, DRB1*0701-DQA1*0201-DQB1*0201, DRB1*0101-DQA1*0101-DQB1*0501, DRB1*1101-DQA1*0501-DQB1*0301, DRB1*03011-DQA1*0501-DQB1*0201, and DRB1*1301-DQA1*0103-DQB1*0603. A genetic distance analysis between the Polish and other world populations tested for HLA class II indicates that the Wielkopolska community is close to geographically close, rather than linguistically related populations from Europe. More generally, a good agreement between genetics and geography is found for DRB1 and DQB1 polymorphisms in Europe, suggesting that these two loci are highly informative for assessing historical relationships among humans.

Selectivity of the major histocompatibility complex class II presentation pathway of cortical thymic epithelial cell lines

Major histocompatibility complex (MHC) restriction of the immune response is established during positive selection of T cells in the thymus. This occurs mainly through interactions of T cell receptor of developing thymocytes with MHC/peptide ligands on cortical thymic epithelial cells (TEC). An ongoing controversy concerns the origin and the role of peptides involved in the positive selection of thymocytes. Evidence provided here shows that processing of MHC class II complexes in cortical TEC differs from that of medullary TEC. Removal of the invariant chain associated with MHC class II complexes was rapid and complete in medullary TEC which present peptides from both exogenous and cytosolic origin. In cortical TEC, a large fraction of class II dimers remained associated with a 10-12-kDa fragment of invariant chain (Ii). Incomplete removal of Ii correlated with the inability of cortical TEC to present peptides from exogenous origin. However, presentation of peptides from cytosolic proteins by cortical TEC remained possible. Thus, most peptides from exogenous proteins may be excluded from participating in positive selection of CD4+ T cells by a mechanism limiting Ii breakdown.

Inhibitor (IK) of IFN-gamma induced HLA class II antigens expression also inhibits HLA class II constitutive expression in the human Raji B cell line

The expression of major histocompatibility complex (MHC) class II antigens is constitutive in professional antigen presenting cells (APCs) but can also be induced by interferon-gamma (IFN-gamma) on the majority of the non professional APCs (e.g. fibroblasts). We have recently characterised a new factor called IK which is an efficient inhibitor of IFN-gamma induction of MHC class II antigens expression. Here, we demonstrate a novel role for IK in MHC class II expression since over-expression of this protein by stable transfection into human B cells led to a total disappearance of constitutive MHC class II mRNA expression. The class II transactivator (CIITA) is necessary for both constitutive and IFN-gamma induced MHC class II expressions. Examination of CIITA mRNA in IK stably transfected clones revealed a marked reduction of CIITA mRNA transcription. Taken together these results demonstrate that the IK protein plays a key role in the constitutive expression of MHC class II antigens and that inhibition induced by IK is upstream of CIITA in this regulatory pathway.

HLA class II-mediated death is induced via Fas/Fas ligand interactions in human splenic B lymphocytes

HLA class II molecules, expressed on the surface of antigen-presenting cells, are responsible for the presentation of antigen-derived peptides to CD4+ helper T lymphocytes. Signaling via these molecules initiates the generation of second messengers leading to programed cell death (PCD) of activated B lymphocytes. The present study examined the mechanism of HLA class II-mediated apoptosis and describes the essential role of the molecule Fas and its ligand (FasL). FasL was expressed in B lymphocytes after stimulation via HLA class II or with phorbol esters. Expression of FasL protein was significantly increased in 50% of B lymphocytes after stimulation via HLA class II, and the level of FasL mRNA was also increased either by activation with phorbol esters and ionomycin or by signaling via HLA class II. Although HLA class II signaling did not change the expression of the Fas molecule, it did lead to increased sensitivity to Fas-mediated apoptosis. The crucial role of Fas/FasL interactions was confirmed by the absence of cell death via HLA class II in B cells lacking Fas expression, and by the significant inhibition of HLA class II-mediated apoptosis in the presence of either an antagonistic anti-Fas or anti-FasL antibody. These data demonstrate FasL expression on activated human B lymphocytes and support the idea that antigen presentation could contribute to the regulation of lymphocyte populations via Fas and FasL interactions.

HLA class II antigens and T lymphocytes in human nasal epithelial cells. Modulation of the HLA class II gene transcripts by gamma interferon

BACKGROUND

Nasal polyps are characterized by a proliferation of the epithelial layer of the mucosa, cellular infiltrates and other pathological changes; however the mechanisms involved in polyp pathogenesis remain largely unclear.

OBJECTIVES

We have taken two different approaches to study the cellular events involved in nasal polyposis.

METHODS

First, through use of immunohistochemical methods, we have studied the expression of HLA class II antigens in epithelial cells of nasal polyps and the distribution of lymphocytes in the epithelium and in the subepithelial layer in patients with clinical conditions, such as asthma, atopy, aspirin intolerance or cystic fibrosis, and in subjects with an absence of concomitant diseases. Second, in order to investigate whether HLA class II expression is controlled at the pre- or post-transcriptional level, we studied the effect of interferon gamma (INF gamma) on epithelial cells in primary culture, which were derived from HLA class II negative and HLA class II positive nasal polyps. Total RNA was extracted from the cells and reverse-transcribed, and the c-DNA corresponding to DR, DP, DQ loci was amplified by PCR.

RESULTS

Expression of HLA class II antigens by the epithelia of nasal polyps was more common in the presence rather than in the absence of concomitant asthma, atopy or cystic fibrosis (59% versus 40%). HLA-DR was the only HLA class II antigen expressed in the seven polyps taken from cystic fibrosis patients. The number of CD8+ cells was significantly higher in polyps associated with known clinical conditions and HLA class II antigen expression than it was in 'isolated' polyps and in HLA class II negative polyps. RNA transcripts for at least one or all three HLA-DR, DP and DQ antigens were detected in 10 cultures of the II HLA class II positive polyps. Conversely, 8 of 10 cultures derived from HLA class II negative polyps did not express HLA class II transcripts in the absence of INF gamma. Adding INF gamma (100 U/ml) to the latter cell cultures caused expression of transcripts of one or more HLA class II genes.

CONCLUSIONS

We have shown that HLA class II antigens were more frequently detected in polyps of patients with an identified clinical syndrome than in those of asymptomatic subjects. Our results also suggest that IFN gamma regulates expression of HLA class II antigens in airway epithelial cells of the nasal polyps at the transcriptional level, and that cultured cells from nasal polyps represent a suitable model to investigate immune mechanisms involved in diseases such as atopy, asthma and cystic fibrosis.

Two widely used anti-DR alpha monoclonal antibodies bind to an intracellular C-terminal epitope

In this report we show that two widely-used monoclonal antibodies, TAL-1B5 and DA6.147, which react with the HLA-DR alpha chain on immunoblots, recognize the C-terminal intracellular tail of this HLA-DR subunit. We demonstrate that both MoAbs react with a synthetic peptide representing the intracellular C-terminal tail of the DR alpha chain and that mutant DR molecules lacking this part of the alpha chain lose reactivity with TAL-1B5 and DA6.147, both in Western blot analysis and in intracellular FACS staining.

[Antigen presentation and macrophages]

T-cells recognize antigenic peptides associated with HLA molecules belonging to Class I (HLA-A, -B, or -C) or Class II (HLA-DP, -DQ, -DR). Roughly, Class I HLA molecules represent antigens to cytotoxic CD8+ T-cells and Class II HLA molecules to helper CD4+ T-cells. Class II HLA molecules primarily present "exogenic" peptides that penetrate within cells by endocytosis, whereas Class I HLA molecules present "endogenic" peptides produced within cells. In both cases, the mechanisms of antigen presentation are closely liked to the biosynthesis of HLA molecules and to the expression of other molecules including proteasome (LMP) and the peptide transporters (TAP) needed to transport peptides through the endoplasmic reticulum in the case of Class I molecules, and invariant chain (Ii) and HLA-DM antigens in the case of Class II molecules. In addition, "exogenous" presentation by Class I molecules has recently been described, and may be relatively specific of phagocytic cells such as macrophages.

Differences in endogenous peptides presented by HLA-B*2705 and B*2703 allelic variants. Implications for susceptibility to spondylarthropathies

The association between HLA-B27 and spondylarthropathies is currently being reinvestigated in the light of HLA-B27 subtyping. At least 11 different subtypes have been described among which B*2703, B*2706, and B*2709 could be less closely associated with disease at the population level. Differences in the presentation of antigenic peptides by these subtypes could be related to differences in disease susceptibility. We focused our work on the comparison of B*2705 and B*2703 which differ at a single position at residue 59 in pocket A of the peptide binding groove. Endogenous peptides from the human C1R line transfected by B*2705 or B*2703 were acid-eluted and separated by HPLC. Major individual fractions were sequenced by Edman NH2-terminal degradation. Differences observed between B*2705 versus B*2703 individual ligands were confirmed in an in vitro stabilization assay with T2-B*2705 or B*2703 transfected cells in the presence of synthetic peptides. One B*2705 associated peptide is derived from the sequence 169-179 in the second extracellular domain of several HLA class I molecules including HLA-B27. This sequence (RRYLENGKETL) is highly homologous to a previously reported sequence (LRRYLENGK) sharing similarities with proteins from enteric bacteria. We show here that it is naturally presented as a major endogenous peptide by B*2705 and B*2702 disease-associated subtypes and not by B*2703.

Analysis of HLA haplotypes in families with type 1 diabetes mellitus in La Réunion island

To analyse HLA and insulin-dependent diabetes mellitus (IDDM) association in the ethnically mixed population of La Réunion island, we carried out a family study on 70 diabetic subjects. HLA-DQA1, -DQB1 and -DRB1 typing was performed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP), completed by PCR-sequence-specific oligonucleotide (SSO) and PCR-sequence-specific priming (SSP). Haplotype-relative risks (HRR) were determined with the non-transmitted parental haplotypes as controls, and relative risks (RR) were calculated with a classical case-control study. The most significant risks were found for the cis and trans combinations between DQA1*03 or *0501 (Arg52+) and DQB1*02 or *0302 (Asp57-) alleles, suggesting a direct role for the HLA-DQ heterodimer in IDDM susceptibility. Interestingly, due to the mixed origin of the population, the trans-encoded DQ molecules in the (DR3)-DQA1*0501-DQB1*02/(DR4)-DQA1*03-DQB1*0302 subjects were also found cis-encoded in patients with the (DR7 or 9)-DQA1*03-DQB1*02 haplotype and in a patient with the rare (DR11)-DQA1*0501-DQB1*0302 haplotype. A relative predispositional effect (RPE) analysis gave significant haplotype-IDDM+ associations in the following order: (DR3)-DQA1*0501-DQB1*02 > (DR4)-DQA1*03-DQB1*0302 > (DR9)-DQA1*03- DQB*02 > (DR7)-DQA1*03-DQB1*02 > (DR2)-DQA1*01-DQB1*0502. No protective effect remained significant once the susceptible haplotypes were removed. A stratification study showed a stronger influence of the DQ genes than DRB1 alleles within the DR7 haplotypes. On the other hand, IDDM subjects with only one susceptible haplotype had inherited this haplotype more often from their father than from their mother. This paternal effect could be related to the greater risk of IDDM in offspring of diabetic fathers than the risk in offspring of diabetic mothers.

HLA class II signaling mediates cellular activation and programmed cell death

The class II human leucocyte antigens (HLA class II) are principally peptide presentation molecules. Signal transduction by these molecules has also been shown to transmit activation signals in both B and T lymphocytes by a pathway including protein tyrosine kinase activation, an intracellular calcium flux, and both the activation and transcriptional regulation of protein kinase C (PKC) isoforms. Apoptosis can also result from human leukocyte antigen class II stimulation. Inhibitors of gene transcription were used to inhibit activation and, therefore, to distinguish the signal transduction pathways important for apoptosis. This approach provided evidence that cellular activation and apoptosis undertook separate signaling pathways, and that PKC and intracellular calcium were shared between the two pathways, while tyrosine kinase activity was essential for cell activation. Further studies using cord blood B cells showed that these cells were incapable of generating a calcium flux after HLA class II ligation and were not subject to cell death. The importance of sustained levels of calcium for programmed cell death (PCD) was underlined since the restoration of a calcium flux enabled PCD of cord blood B cells via HLA class II. These results demonstrate that HLA class II stimulation initiates two distinct signal transduction pathways.

HLA class II molecule signal transduction leads to either apoptosis or activation via two different pathways

The class II human leukocyte antigens (HLA class II) are constitutively expressed on antigen presenting cells (APC) and are essential for peptide presentation to helper T lymphocytes. Signal transduction by HLA class II molecules on B lymphocytes has been described and has been shown in many cases to induce cellular proliferation. However, since signalling via HLA class II can also lead to apoptosis, it has not been clear how the outcome of the signals is determined. We have distinguished two separate HLA class II-initiated pathways leading to either proliferation or apoptosis of primary human B lymphocytes. Proliferation requires new gene transcription and activation of src family tyrosine kinases. In contrast, apoptosis is significantly increased in the absence of transcription/translation. It is dependent on serine/threonine phosphatases and cytoskeletal mobility. An extracellular source of calcium was essential for apoptosis, suggesting the need for sustained high level of intracellular calcium. Activation of iso-enzymes of the protein kinase C family was needed for both pathways. We therefore conclude that HLA class II molecules can initiate two distinct signalling pathways leading to either proliferation or apoptosis of APC.

Association of HLA class II genes with susceptibility to Crohn's disease

BACKGROUND

Published studies on the association between HLA class II genes and inflammatory bowel disease are contradictory perhaps because of the limited size and ethnic heterogeneity of the populations studied.

AIM

To compare the frequencies of HLA class II genes in a large number of French patients with Crohn's disease and in an ethnically matched control group.

METHODS

344 patients (196 F, 148 M, mean age 23.6 years) with Crohn's disease were molecularly genotyped for the HLA-DQB1 and DRB1 alleles. The results were compared with those for an ethnically matched control population of 488 white adults.

RESULTS

There were two significant variations of alleles at the DQB1 locus: an increase in DQB1*0501 allele frequency (chi 2 = 10.6, corrected p value (pc) = 0.01, odds ratio (OR) = 1.61) and a decrease in DQB1*0602/0603 allele frequencies (chi 2 = 8.43, pc = 0.037, OR = 0.66). DRB1 analysis showed associations with three allelic variations: an increase in the frequencies of DRB1*01 (chi 2 = 12.86, pc = 0.003, OR = 1.75) and DRB1*07 alleles (chi 2 = 11.18, pc = 0.008, OR = 1.58) and a very significant decrease in that of the DRB1*03 allele (chi 2 = 19.7, pc = 9.10(-5), OR = 0.46).

CONCLUSION

The alleles DRB1*01 and DRB1*07 are associated with susceptibility to Crohn's disease. The strong negative association between the DRB1*03 allele and Crohn's disease suggests that the HLA-DRB1*03 allele mediates 'resistance' to Crohn's disease.

Decreased frequency of HLA-DRB1 13 alleles in Frenchwomen with HPV-positive carcinoma of the cervix

Specific types of human papillomaviruses (HPV) are associated with most cases of pre-invasive and invasive neoplasia of the uterine cervix. HLA phenotype influences susceptibility and resistance to viral infections and may therefore influence the course of HPV-associated tumors. Some data suggest that specific HLA class-II alleles may be associated with protection from or susceptibility to papillomavirus-associated lesions, but these results are still controversial. Using molecular probes, we looked for associations between specific DQA1, DQB1, DRB1 HLA class-II alleles, HPV types and cervical cancer. The analysis was performed on a population of 126 patients with invasive cervical cancer. For HLA typing, 165 healthy individuals were taken as controls. The DRB1 1301/02 allele frequency significantly decreased in patients (11%) as compared to controls (29%). This difference in frequency was dependent on the HPV-positive status of tumors and was no longer significant in the group of HPV-negative lesions. The same trends were observed with the DRB1 1301/02-DQA1 0103-DQB1 0603 haplotype frequency. An increase in the frequency of the DRB1 1401/07 and DRB1 03 alleles was observed in patients under 40. Contrary to what has been reported in the literature, no increase in the DRB1 15 allele frequency was observed in our series and only a slight increase in the DQB1 03 frequency was found in patients (70%) compared to controls (58%). In our study, no positive correlations between cervical cancer in Frenchwomen and specific HLA DR-DQ haplotypes has been found. In contrast, a negative correlation between DRB1 1301/ 02 alleles and HPV-positive tumors has been observed. This may suggest a protective effect of DR13 against HPV-associated lesions of the cervix.