RESUMO
Successful expansion of functional CD4(+) CD25(+) regulatory T cells (T(reg)) ex vivo under good manufacturing practice conditions has made T(reg) -cell therapy in clinical transplant tolerance induction a feasible possibility. In animals, T(reg) cells home to both transplanted tissues and local lymph nodes and are optimally suppressive if active at both sites. Therefore, they have the opportunity to suppress both naïve and memory CD4(+) CD25(-) T cells (Tresp). Clinical transplantation commonly involves depleting therapy at induction (e.g. anti-CD25), which favors homeostatic expansion of memory T cells. Animal models suggest that T(reg) cells are less suppressive on memory, compared with naïve Tresp that mediate allograft rejection. As a result, in the context of human T(reg) -cell therapy, it is important to define the effectiveness of T(reg) cells in regulating naïve and memory Tresp. Therefore, we compared suppression of peripheral blood naïve and memory Tresp by fresh and ex vivo expanded T(reg) cells using proliferation, cytokine production and activation marker expression (CD154) as readouts. With all readouts, naïve human Tresp were more suppressible by approximately 30% than their memory counterparts. This suggests that T(reg) cells may be more efficacious if administered before or at the time of transplantation and that depleting therapy should be avoided in clinical trials of T(reg) cells.
Assuntos
Antígenos CD4/imunologia , Memória Imunológica , Subunidade alfa de Receptor de Interleucina-2/imunologia , Linfócitos T Reguladores/imunologia , Separação Celular , Células Cultivadas , Citometria de Fluxo , HumanosRESUMO
The vast majority of new human HLA class I alleles are formed by conversions between existing alleles of the same locus. A notable exception to this rule is HLA-B*4601 formed by replacement of residues 66-76 of the alpha 1 helix of B*1501 by the homologous segment of Cw*0102. This inter-locus recombination, which brings together characteristic elements of HLA-B and HLA-C structure, is shown here to influence function dramatically. Naturally processed peptides bound by B*4601 are distinct from those of its parental allotypes B*1501 and Cw*0102 and dominated by three high abundance peptides. Such increased peptide selectivity by B*4601 is unique among HLA-A,B,C allotypes. For other aspects of function, presence of the small segment of HLA-C-derived sequence in an otherwise HLA-B framework converts B*4601 to an HLA-C-like molecule. Alloreactive cytotoxic T lymphocytes (CTL), natural killer (NK) cells, and cellular glycosidases all recognize B*4601 as though it were an HLA-C allotype. These unusual properties are those of an allotype which has frequencies as high as 20% in south east Asian populations and is associated with predisposition to autoimmune diseases and nasopharyngeal carcinoma.
Assuntos
Genes MHC Classe I , Antígenos HLA-B/imunologia , Antígenos HLA-C/imunologia , Peptídeos/imunologia , Sequência de Aminoácidos , Células Cultivadas , Antígenos HLA-B/genética , Humanos , Células Matadoras Naturais/imunologia , Modelos Moleculares , Dados de Sequência Molecular , Peptídeos/química , Ligação Proteica , Estrutura Terciária de Proteína , Recombinação Genética , Relação Estrutura-Atividade , Linfócitos T Citotóxicos/imunologia , TransfecçãoRESUMO
BACKGROUND: Polymorphism among class I molecules of the major histocompatibility complex (MHC) confers allotypic specificity on the peptides that these molecules bind and present to cytotoxic T lymphocytes. Evolution of new human HLA class I alleles usually involves gene recombination events that replace a segment of one allele with the homologous region of another. In this study, the impact of these evolutionary changes has been assessed by comparison of the peptide-binding specificities of six related HLA-B allotypes. RESULTS: Endogenous peptides bound by HLA-B*5401, HLA-B*5501, HLA-B*5502, HLA-B*5601, HLA-B*6701 and HLA-B*0702 were characterized. Despite differing by 1-9 of the amino-acid residues comprising their peptide-binding sites, all these allotypes share a dominant preference for peptides that have proline at position 2. Polymorphism results in differing selection of carboxy-terminal and secondary anchor residues, but the peptide-binding specificities are sufficiently similar that there is overlap in the repertoires of peptides bound by these allotypes. Complete sequence determination of individual peptides revealed four that could be isolated from two or more allotypes. Members of the closely related HLA-B22 family--HLA-B*5401, HLA-B*5501, HLA-B*5502 and HLA-B*5601--show only minor differences in their peptide-binding specificities. This marked similarity is reflected at the functional level, as alloreactive cytotoxic T lymphocytes generated against HLA-B*5401 and HLA-B*5501 exhibited cross-reactive recognition. CONCLUSION: The isolation of identical endogenously bound peptides from six HLA-B allotypes demonstrates overlap in the repertoires of peptides bound in vivo by different allotypes. We speculate that the shared preference for binding peptides with proline at position 2 reflects a selective pressure to retain this specificity, which may be based upon peptide availability in vivo. Characterization of the overlap between the repertoires of peptides bound by HLA-B allotypes could simplify the development of peptide-based vaccines that are targeted to cytotoxic T cells, as single peptides would be effective for humans of different HLA types.
Assuntos
Antígenos HLA-B/metabolismo , Peptídeos/metabolismo , Sequência de Aminoácidos , Antígenos HLA-B/genética , Humanos , Dados de Sequência Molecular , Prolina/metabolismo , Ligação Proteica , Homologia de Sequência de AminoácidosRESUMO
Class I molecules of the major histocompatibility complex bind peptides derived from cytosolic proteins and display them on the cell surface. This function alerts cytotoxic T cells to the presence of intracellular pathogens. Class I molecule assembly requires the association of the heavy chain with beta 2-microglobulin, accompanied by peptide loading via specific transporters. This study localizes where these assembly steps take place, using monoclonal antibodies recognizing class I molecules in different assembly states to analyze subcellular fractions of the early secretory pathway. The distribution of peptide-loaded class I molecules was more localized than the distribution of the total pool of class I molecules in the early secretory pathway. Loaded molecules colocalized with the peptide transporter, free heavy chains, and the chaperone calnexin in high density rough endoplasmic reticulum (RER) membranes. These data suggest that subunit assembly and peptide acquisition occur at the same intracellular site. Class I molecules also localized to less dense subfractions of the early secretory pathway, which contained comparatively less peptide-loaded molecules than the high density RER fractions, at steady state. Following a 15 degrees C temperature block, class I molecules accumulated in these less dense membrane fractions, indicating that these fractions represent the intermediate compartment where empty class I molecules are trapped in mutant cells. In the presence of cycloheximide, a pool of class I molecules recycling to the RER was detected suggesting empty molecules recycle to acquire peptide.
Assuntos
Antígenos de Histocompatibilidade Classe I/metabolismo , Membro 2 da Subfamília B de Transportadores de Cassetes de Ligação de ATP , Transportadores de Cassetes de Ligação de ATP/metabolismo , Transporte Biológico , Compartimento Celular/imunologia , Centrifugação com Gradiente de Concentração , Retículo Endoplasmático Rugoso/metabolismo , Humanos , Linfoma de Células B , Frações Subcelulares/imunologia , Frações Subcelulares/metabolismo , Células Tumorais CultivadasRESUMO
The relative contributions of putative T-cell receptor (TCR)-contacting and peptide-binding residues of a major histocompatibility complex (MHC) class II restriction element to serologic and antigen-specific T-cell recognition were investigated by site-specific mutagenesis. Amino acids 70 and 71 in the DR beta 1 domain of DR4 Dw10 are uniquely differnet from the other Dw subtypes of DR4. Residue 70 is predicted to be located at the membrane-distal surface of the class II molecule, where it may influence T-cell recognition by a direct interaction with a TCR. Residue 71 is predicted to form part of the antigen-binding groove where its influence on T-cell recognition may be mediated indirectly via an effect on peptide binding. Transfected murine L cells were produced expressing the products of DR4 Dw10B genes in which the codons for residues 70 and 71 had been mutated towards DR4 Dw14. Support for the predicted orientations of beta-chain residues 70 and 71 was lent by the observation that only residue 70 plays an important role in the formation of a serologic determinant. Mutation of this residue was sufficient to produce recovery of recognition by a human monoclonal antibody, NI, which has specificity for all the DR4 subtypes with the exception of DR4 Dw10. The human T-cell clone HA1.7, specific for influenza virus hemagglutinin (HA) peptide 307-319 and restricted by DR1 Dw1, exhibits degeneracy of MHC restriction on the DR4 Dw subtypes with the exception of DR4 Dw10.(ABSTRACT TRUNCATED AT 250 WORDS)
Assuntos
Artrite Reumatoide/imunologia , Antígenos HLA-D/imunologia , Antígeno HLA-DR4/imunologia , Receptores de Antígenos de Linfócitos T/imunologia , Linfócitos T/imunologia , Animais , Artrite Reumatoide/sangue , Sítios de Ligação , Células Clonais , Suscetibilidade a Doenças/sangue , Antígenos HLA-D/sangue , Antígenos HLA-D/genética , Antígeno HLA-DR4/sangue , Antígeno HLA-DR4/genética , Cadeias HLA-DRB1 , Camundongos , Mutagênese Sítio-Dirigida , Conformação ProteicaRESUMO
A seven-year-old iatrogenically immunosuppressed girl developed simultaneous bilateral iris tumors associated with granulomatous iridocyclitis, splenomegaly, and an immunoblastic pleocytosis. Serologic studies suggested a current active Epstein-Barr virus infection. Tumor biopsy showed a polyclonal plasmacytoid lymphoproliferative process, establishing the diagnosis of posttransplant lymphoproliferative disorder. Low-dose local irradiation produced rapid and complete iris tumor regression with restoration of vision in both eyes. To our knowledge, this is the first report of ocular involvement in posttransplant lymphoproliferative disorder.
Assuntos
Terapia de Imunossupressão , Neoplasias da Íris/diagnóstico , Transtornos Linfoproliferativos/diagnóstico , Plasmocitoma/diagnóstico , Criança , Ciclosporina/uso terapêutico , Feminino , Rejeição de Enxerto , Humanos , Neoplasias da Íris/etiologia , Neoplasias da Íris/radioterapia , Transplante de Fígado , Transtornos Linfoproliferativos/etiologia , Transtornos Linfoproliferativos/radioterapia , Plasmocitoma/etiologia , Plasmocitoma/radioterapia , Complicações Pós-OperatóriasRESUMO
Although the T-cell response to allogeneic cells is typically regarded as a detrimental phenomenon responsible for rejection of transplanted allografts and graft-vs.-host disease following haematopoietic stem cell transplantation, beneficial components also exist within the alloreactive population. Alloreactive T cells specific for tumour antigens can contribute to the elimination of malignant cells, and alloantigen-specific regulatory T cells can promote transplant tolerance. The challenge is to separate the good from the bad. We review how the identification, isolation and manipulation of beneficial alloreactive T cells has grown from a greater understanding of the molecular basis of the T-cell alloresponse and how alloaggression could be exploited for immunotherapy.
Assuntos
Doença Enxerto-Hospedeiro/imunologia , Efeito Enxerto vs Tumor/imunologia , Transplante de Células-Tronco Hematopoéticas , Isoantígenos/imunologia , Neoplasias/imunologia , Linfócitos T/imunologia , Transferência Adotiva , Doença Enxerto-Hospedeiro/etiologia , Humanos , Ativação Linfocitária/imunologia , Neoplasias/terapia , Linfócitos T/transplante , Tolerância ao Transplante/imunologia , Transplante HomólogoRESUMO
A series of transfected L cell lines were generated expressing the products of wild-type or recombinant HLA-DR1/H-2Ek beta-chain-encoding genes paired to DR alpha or E alpha. The recombinant genes were created by reciprocal exchange of the gene segments encoding the amino (NH2)-terminal and carboxy (COOH)-terminal halves of the beta 1 domain and the beta 2 domain. The majority of the serologic determinants, predicted from the genetic composition of the class II dimers, were expressed indicating that no gross conformational changes were induced by the creation of the interspecies recombinant molecules. Subtle conformational variation was detected by the anti-H-2Eb,k,s mAb Y17. Epitope expression was dependent on the presence of the E alpha-chain and NH2-terminal sequence from the beta 1 domain of H-2Ek. Substitution of DR1 sequence in either region led to loss of recognition by Y17. This pattern of reactivity maps the Y17 epitope either to the E alpha-chain or to an exposed sequence on the fourth strand of the beta sheet of the beta 1 domain. If the Y17 epitope is located on the E alpha-chain this raises the interesting possibility that the conformation of this chain, which is invariant by sequence, may vary according to the beta-chain with which it is coexpressed. The ability of the recombinant class II dimers to present Ag to the pigeon cytochrome c-specific, H-2Ek-restricted T cell hybridoma 2B4 was assessed. Transfected L cells expressing E beta k paired to E alpha or DR alpha presented Ag with equal efficiency, and the beta 2 domain of H-2Ek could be substituted with the equivalent region from DR1 without any loss of response. Wild-type DR1 failed to function as a restriction element, however, substitution of the COOH-terminal portion of the beta 1 domain with the equivalent sequence from H-2Ek was sufficient to produce a partial recovery of Ag recognition. Cells expressing a recombinant beta 1 domain comprising the COOH-terminal sequence from H-2Ek and the NH2-terminal sequence from DR1 presented Ag when paired to DR alpha but failed to do so when paired to E alpha. This indicates that a subtle conformational disturbance caused by mismatching of the NH2-terminal region of the beta-chain and the alpha-chain can have pronounced effects on T cell recognition.(ABSTRACT TRUNCATED AT 400 WORDS)
Assuntos
Antígenos H-2/imunologia , Antígenos HLA-DR/imunologia , Linfócitos T/imunologia , Sequência de Aminoácidos , Anticorpos Monoclonais , Epitopos/análise , Humanos , Dados de Sequência Molecular , Conformação Proteica , Proteínas Recombinantes/imunologia , Relação Estrutura-AtividadeRESUMO
Foreign allogeneic major histocompatibility complex (MHC) class I and class II molecules elicit an exceptionally vigorous T-cell response. A small component of the alloresponse comprises CD4+ T cells that recognize allogeneic MHC indirectly after processing into peptide fragments that are bound and presented by self-MHC class II. The majority of alloreactive T cells directly recognize intact allogeneic MHC molecules expressed on foreign cells. Some alloreactive T-cell interactions with allogeneic MHC molecules are indifferent to the bound peptide, but evidence suggests that most show specificity to peptide. The vigor and diversity of the direct alloreactive T-cell response can therefore be explained by summation of numerous responses to each of the peptides in the novel set bound by allogeneic MHC molecules. Structural studies definitively show that the overall mechanism of T-cell receptor (TCR) recognition of self-MHC and allogeneic MHC molecules is similar. Many alloreactive T cells recognize several different combinations of MHC and bound peptide that do not necessarily possess structural homology. Flexibility within the TCR structure allows adaptation to the different contact surfaces. Crossreactivity seems to be an intrinsic property of the TCR required, because a single TCR must possess the ability to interact with both self-MHC during positive selection and at least one combination of foreign antigenic peptide presented by self-MHC. Recognition of allogeneic MHC molecules is an inadvertent consequence of the need for TCR crossreactivity.
Assuntos
Isoantígenos , Complexo Principal de Histocompatibilidade/imunologia , Receptores de Antígenos de Linfócitos T/imunologia , Linfócitos T/imunologia , Animais , Humanos , Isoantígenos/química , Isoantígenos/imunologia , Conformação ProteicaRESUMO
Tapasin plays a critical role in promoting peptide binding by major histocompatibility complex (MHC) class I molecules in the endoplasmic reticulum. In its absence, cell surface expression of most allotypes is significantly reduced. Two exceptions are HLA-A*0201 and HLA-B*2705. In this study, the repertoire of peptides bound endogenously by these allotypes in the absence of tapasin was examined and stability of the HLA class I/peptide complexes assessed. Similar quantities of peptides were recovered from B*2705 complexes expressed in the absence and presence of tapasin and the composition of the peptide pools were not radically different. However, the stability of B*2705 molecules expressed at the surface of tapasin-deficient cells was found to be reduced which suggests there are subtle changes to the peptide repertoire. The impact of the absence of tapasin was more dramatic for A*0201. Although equivalent levels of cell surface A*0201 are expressed in the presence and absence of tapasin, very little A*0201 glycoprotein was recovered from tapasin-deficient cells suggesting the complexes readily dissociate. Consistent with reduced stability, A*0201 complexes were found to be rapidly lost from the surface of tapasin-deficient cells. Analysis of the small quantity of endogenously bound peptides recovered from A*0201 expressed in the absence of tapasin revealed a complex mixture typical of A*0201 molecules expressed in normal cells. Therefore these molecules are unable to exploit the alternative supply of TAP-independent A*0201-binding peptides present in the endoplasmic reticulum. Loading of A*0201 with peptides from both TAP-dependent and TAP-independent sources is significantly compromised without tapasin.
Assuntos
Antiporters/metabolismo , Antígenos HLA-A/metabolismo , Imunoglobulinas/metabolismo , Antígenos de Superfície/metabolismo , Células Cultivadas , Citometria de Fluxo , Antígeno HLA-A2 , Antígenos HLA-B/metabolismo , Humanos , Proteínas de Membrana Transportadoras , Ligação Proteica/imunologiaRESUMO
Previous studies showed the human MHC class I heavy chain HLA-B*7301 has a sequence very divergent from other class I alleles. Despite the unusual sequence, we predicted B*7301 would retain the peptide-binding function typical of other HLA-A, B and C glycoproteins, and sequence similarity to B*2705 in a region of the peptide-binding site known as the B pocket suggested B*7301 would bind peptides with Arg at position 2. To test this hypothesis, the peptide-binding specificity of B*7301 was investigated. Sequence analysis of peptides bound endogenously by B*7301 indeed found selectivity for nonamer peptides possessing Arg at position 2 and a preference for small nonpolar residues such as Pro or Ala at the C terminus was also revealed. B*7301 therefore possesses the potential to function as a conventional antigen presenting class I glycoprotein. Functional similarities between B*7301 and B*2705 are discussed in the context of the association of B*27 subtypes with susceptibility to ankylosing sponylitis and arthritic diseases.
Assuntos
Antígenos HLA-B/imunologia , Peptídeos/imunologia , Sítios de Ligação , Linhagem Celular Transformada , Humanos , Peptídeos/químicaRESUMO
A radioimmunoassay was developed for salmonid melanin concentrating hormone (MCH) and used to measure immunoreactive (ir)MCH in the hypothalamus and pituitary of trout (Salmo gairdneri) and eels, (Anguilla anguilla) maintained under different regimes of background color. In trout, 95% of the total irMCH was located in the pituitary gland. The amount of MCH in both pituitary and hypothalamus was increased when white-adapted trout were transferred to a black background. In eels, a similar change of background led to an accumulation of MCH in the pituitary but not in the hypothalamus. The results suggest that MCH is released from the neurohypophysis in association with physiological color change. Neurointermediate lobes of trout and eels released both ir alpha MSH and irMCH when they were cultured in vitro. The release of alpha MSH was significantly enhanced when endogenous MCH was immunoabsorbed by MCH antiserum added to the culture medium. The results indicate that MCH can induce pallor in fish not only by its peripheral effect on the melanophores but also by an inhibitory action on the release of alpha MSH from the pituitary.
Assuntos
Anguilla/fisiologia , Hormônios Hipotalâmicos , Melaninas/farmacologia , Hormônios Estimuladores de Melanócitos/metabolismo , Hormônios Hipofisários/farmacologia , Salmonidae/fisiologia , Truta/fisiologia , Animais , Hipotálamo/efeitos dos fármacos , Hipotálamo/metabolismo , Técnicas In Vitro , Melaninas/fisiologia , Melanóforos/efeitos dos fármacos , Melanóforos/fisiologia , Hipófise/efeitos dos fármacos , Hipófise/metabolismo , Hormônios Hipofisários/fisiologia , Pigmentação da PeleRESUMO
Evidence of an immune mediated graft-versus-leukaemia effect has led to the belief that T and NK cell based adoptive immunotherapy can constitute effective treatment for relapsed leukaemias. However, work on solid tumours has shown this strategy may be hampered, by an immune escape mechanism in which tumour secreted immunosuppressive factors compromise T and NK cell function. Indeed, acute myeloid leukaemia (AML) cells secrete immunosuppressive factors that block the synthesis of Th1 type cytokines in T cells. We demonstrate here that this immunosuppression, mediated by both HL60 AML cell line and primary AML blasts, inhibits T and NK cell proliferation but not cytolytic activity. Supernatants from HL60 cell line and primary AML blasts inhibited T cell proliferation to mitogenic and alloantigen stimulation but had no effect on cytolytic function. Similarly, the proliferation of NK cells to IL-2 and IL-15 stimulation was inhibited whilst their cytolytic function, shown by lysis of AML blasts, K562 and Daudi cells remained unaffected. The failure of T and NK cells to proliferate was not due to effector cell apoptosis. Indeed, removal of lymphocytes from the immunosuppressive environment partially restored their capacity to respond to mitogenic stimulation. T cells exposed to immunosuppressive supernatants did not increase expression of mitotic inhibitory proteins that arrest cell division, thereby ruling this out as a mechanism of operation for this immunosuppression. T cell expansion requires antigen stimulation, usually provided in the form of AML blasts, therefore our data suggest that NK cells may be more practical for the immunotherapy of AML.
Assuntos
Imunoterapia Adotiva , Células Matadoras Naturais/imunologia , Leucemia Mieloide Aguda/imunologia , Leucemia Mieloide Aguda/terapia , Fatores Supressores Imunológicos/metabolismo , Linfócitos T/imunologia , Divisão Celular , Citotoxicidade Imunológica , Efeito Enxerto vs Leucemia/imunologia , Células HL-60 , Humanos , Interleucina-15/farmacologia , Interleucina-2/farmacologia , Isoantígenos/administração & dosagem , Células K562 , Células Matadoras Naturais/patologia , Leucemia Mieloide Aguda/patologia , Ativação Linfocitária , Mitógenos/farmacologia , Linfócitos T/patologia , Células Tumorais CultivadasRESUMO
HLA-B*0801 is unique among HLA-B allotypes in having dominant amino acid anchors at positions 3 and 5 of the peptide-binding motif. HLA-B*0802 is a variant of HLA-B*0801 in which the Bw6 sequence motif is replaced by a Bw4 sequence motif. This change, involving substitutions at positions 77, 80, 81, 82, and 83 of the B*08 heavy chain, is probably the result of a single evolutionary event of interallelic conversion. Moreover, the difference between B*0802 and B*0801 is sufficient to stimulate a cytotoxic T-cell response. To assess further the functional impact of the Bw4 motif on a B8 background, we compared the peptide-binding specificity of the B*0801 and B*0802 allotypes by sequencing the mixture of peptides endogenously bound to B*0802 and 12 individual peptides purified from that mixture. The HLA-B*0802 allotype, while able to bind some peptides bound by B*0801, has a broader repertoire of endogenously bound peptides than B*0801: the peptides bound by B*0802 are more variable in length and exhibit greater diversity in the carboxyl-terminal amino acid which interacts with the F pocket.
Assuntos
Antígenos HLA-B/química , Linfócitos T/imunologia , Sequência de Aminoácidos , Linhagem Celular , Antígenos HLA-B/imunologia , Humanos , Modelos Moleculares , Conformação Proteica , Células Tumorais CultivadasRESUMO
Previously, we reported overlap in the repertoires of peptides endogenously bound by a group of HLA-B allotypes related to HLA-B7. Extending such analysis to four members of the B17 family and seven members of the B15 family shows that allotypes that share sequence identity in the alpha 1 helix of the class I heavy chain possess markedly similar peptide-binding specificities. Members of the B17 family share a preference for peptides with serine, threonine, or alanine at position 2 and aromatic residues at the carboxyl terminus. Strikingly, the presence of a segment of the B17 alpha 1 helix in B*1516 and B*1517 confers the B17-like peptide-binding motif. The strong influence of natural variation in the alpha 1 helix is exemplified by the differences in peptide-binding specificity of B15 allotypes related by conversion events that replaced segments of the alpha 1 helix. In contrast, evolutionary changes that are confined to the alpha 2 domain confer less dramatic change. They do not perturb the primary anchors of the peptide-binding motif but can modulate the specificity through development and diversification of secondary anchors. Our results, in combination with those obtained previously for other HLA-B allotypes, suggest a general trend whereby polymorphism in the alpha 1 helix is the overriding influence on peptide-binding specificity of HLA-B allotypes, while amino acid substitutions in the alpha 2 domain play a more modulatory role.
Assuntos
Epitopos/genética , Antígenos HLA-B/química , Antígenos HLA-B/genética , Peptídeos/química , Peptídeos/imunologia , Polimorfismo Genético/imunologia , Alelos , Sequência de Aminoácidos , Epitopos/metabolismo , Evolução Molecular , Antígenos HLA-B/fisiologia , Humanos , Isoantígenos/genética , Isoantígenos/metabolismo , Dados de Sequência Molecular , Peptídeos/metabolismo , Estrutura Terciária de Proteína , Homologia de Sequência de Aminoácidos , Relação Estrutura-AtividadeRESUMO
Serological heterogeneity in HLA-B46 antigens has been described. Previous studies have identified B*4601 as the allele encoding the "strong" B46 antigen found in Chinese populations. Serological characterization of a Vietnamese family revealed a "weak" B46 antigen. Complementary DNA for the HLA-A, B and C alleles of three family members were cloned and the coding regions sequenced. The allele encoding the weak B46 antigen has the same coding sequence as B*4601, demonstrating that the antigenic differences are not due to polymorphism in the amino acid sequence of the HLA-B heavy chain. The recently described HLA-B*1525 and HLA-Cw*0403 alleles were also found to segregate in this Vietnamese family.
Assuntos
Alelos , DNA Complementar/genética , Antígenos HLA-B/genética , Humanos , VietnãRESUMO
HLA-B67 is an uncommon antigen that has been defined by serological crossreactivity with the HLA-B7 and HLA-B16 (B38 and B39) antigens. It is found at highest frequency in certain Oriental populations and has been best defined in the Japanese. Nucleotide sequencing of cDNA encoding B67 reveals the B*6701 allele to be a subtype of B39 which differs from B*39011 by substitution at residues 67-71 of the alpha 1 helix. In the region of difference B*6701 is identical in sequence to B7, B22, B27 and related molecules that express the epitope recognized by the ME1 monoclonal antibody. That the HLA-B67 molecule binds strongly to the ME1 antibody was demonstrated by immunoprecipitation and cell surface binding assays. Identical B*6701 nucleotide sequences were obtained for the B67 alleles isolated from 2 unrelated Japanese and 1 North American caucasoid.
Assuntos
Anticorpos/genética , Epitopos/genética , Antígenos HLA-B/genética , Alelos , Sequência de Aminoácidos , Anticorpos/análise , Anticorpos/imunologia , Sequência de Bases , DNA/genética , Epitopos/análise , Epitopos/imunologia , Antígenos HLA-B/análise , Antígenos HLA-B/imunologia , Antígeno HLA-B38 , Humanos , Dados de Sequência MolecularRESUMO
The nucleotide sequence of cDNA encoding the HLA-B73 antigen was determined; it is unusually divergent, differing from other HLA-B alleles by 44-77 nucleotide substitutions. Features that distinguish the B*7301 heavy chain from other HLA-B heavy chains include multiple substitutions in the alpha 3 domain and a duplication-deletion within the transmembrane region that increases the length of B*7301 compared to other HLA-B heavy chains. The duplication-deletion is shared with subsets of B alleles from the homologous gorilla (Gogo-B) and chimpanzee (Patr-B) loci. Other unusual features of B*7301 are individually shared with certain alleles of the HLA-A, HLA-C, HLA-F, Gogo-B and Patr-B loci. The B*7301 molecules has sequence elements in common with members of the B7 crossreacting group in the alpha 1 domain and is shown to possess the ME1 epitope, which is held in common with the B7, B22, B27, B42 and B67 antigens. B*7301 has a unique cysteine at position 270 of the alpha 3 domain which appears accessible but probably does not form disulphide-bonded B*7301 dimers in cell membranes. B*7301 represents a newly discovered but ancient lineage of HLA-B alleles that appears poorly represented in the modern human population.