Avaliação de assimetria nas arcadas dentárias de indivíduos com oclusão normal e má oclusão de Classe II

A assimetria das arcadas dentárias constitui um assunto de grande importância estudado por profissionais de Ortodontia na elaboração de um diagnóstico correto, planejamento e execução de um tratamento ortodôntico bem sucedido. O objetivo deste estudo foi avaliar o grau de assimetria das arcadas dentárias em indivíduos com oclusão normal e má oclusão de Classe II, divisão 1 e 2, bem como o dimorfismo sexual existente. Foram avaliados 180 pares de modelos de estudo de indivíduos do sexo masculino e feminino, na faixa etária de 12 a 21 anos, divididos em 3 grupos de 60 pares de modelos, de acordo com a má oclusão. Os grupos foram classificados em: Grupo 1 - indivíduos com oclusão normal, Grupo 2 - indivíduos com má oclusão de Classe II divisão 1 (Cl II 1), e Grupo 3 - indivíduos com má oclusão de Classe II divisão 2 (Cl II 2). Os modelos foram medidos utilizando-se um aparelho inédito, idealizado e fabricado exclusivamente para a análise de assimetria das arcadas dentárias. Para a análise de assimetria foram realizadas 2 medições angulares desvio de linha média (DLM), posicionamento dos caninos (PC) e 3 lineares distância dos caninos à rafe palatina (DC), distância inter-caninos (DIC), posicionamento dos primeiros molares no sentido ântero-posterior (PM). Concluiu-se que a ocorrência de assimetria nas arcadas dentárias independe da má oclusão. O Grupo 1 apresentou um menor grau de assimetria nas arcadas dentárias em relação aos grupos 2 e 3, os quais apresentaram um grau de assimetria semelhante. O grau de assimetria nas arcadas dentárias inferiores, nos 3 grupos, foi maior do que nas arcadas dentárias superiores. A direção do desvio da linha média apresentou uma correlação inversamente proporcional do lado em que o molar se apresentava mesializado, nas arcadas superior e inferior dos três grupos, com exceção da arcada superior no Grupo 2 (Classe II divisão 1). Houve dimorfismo sexual estatisticamente significante para algumas medidas, porém é importante considerar os baixos valores e a disposição, destas diferenças, entre as medidas realizadas, a qual revela ter se tratado de dados obtidos ao acaso.

AVALIAÇÃO COMPARATIVA DA AGRADABILIDADE FACIAL DE PACIENTES COM MÁ-OCLUSÃO DE CLASSE II TRATADOS COM COMPENSAÇÃO DENTÁRIA OU CIRURGIA ORTOGNÁTICA

O objetivo deste estudo foi avaliar, por meio de fotografias em norma frontal e lateral, a agradabilidade facial obtida com o tratamento de pacientes portadores de má oclusão de classe II. Foram selecionados dois grupos de pacientes que receberam abordagens diferentes de tratamento, um submetido à cirurgia ortognática e o outro à compensação dentária. As fotografias em norma lateral e frontal obtidas ao início e final do tratamento foram distribuídas aleatoriamente e dispostas em apresentação de multimídia para serem submetidas à avaliação subjetiva de indivíduos leigos e ortodontistas, em uma escala linear crescente. Os resultados foram avaliados comparativamente entre os grupos leigos e ortodontistas, entre os estágios inicial e final do tratamento e entre os grupos tratados com a abordagem cirúrgica e compensatória, com o intuito de estabelecer qual das duas abordagens oferece maior agradabilidade facial. Concluímos que houve proximidade entre as avaliações de leigos e ortodontistas quanto à agradabilidade facial, sendo os leigos mais críticos. Tanto leigos quanto ortodontistas deram escores significativamente maiores para as fotos pós-tratamento nos casos compensatórios e cirúrgicos; os casos cirúrgicos em norma lateral obtiveram os resultados melhores.

HLA-G expression in melanoma: A way for tumor cells to escape from immunosurveillance

Considering the well established role of nonclassical HLA-G class I molecules in inhibiting natural killer (NK) cell function, the consequence of abnormal HLA-G expression in malignant cells should be the escape of tumors from immunosurveillance. To examine this hypothesis, we analyzed HLA-G expression and NK sensitivity in human malignant melanoma cells. Our analysis of three melanoma cell lines and ex vivo biopsy demonstrated that (i) IGR and M74 human melanoma cell lines exhibit a high level of HLA-G transcription with differential HLA-G isoform transcription and protein expression patterns, (ii) a higher level of HLA-G transcription ex vivo is detected in a skin melanoma metastasis biopsy compared with a healthy skin fragment from the same individual, and (iii) HLA-G protein isoforms other than membrane-bound HLA-G1 protect IGR from NK lysis. It thus appears of critical importance to consider the specific role of HLA-G expression in tumors in the design of future cancer immunotherapies.

T cell positive selection by a high density, low affinity ligand

Interaction of the αβ T cell receptor (TCR) with major histocompatibility (MHC) molecules occupied with any of a large collection of peptides derived from self proteins is a critical step in driving T cell “positive” selection in the thymus. Interaction with this same pool of self-peptide/MHC ligands deletes T cells with potential self-reactivity. To examine how T cells survive both of these processes to form a self-tolerant mature repertoire, mice were constructed whose entire class II MHC IEk specific repertoire was positively selected on a single peptide covalently attached to the IEk molecule. In these mice T cells were identified that could respond to a variant of the positively selecting peptide bound to IEk. The affinities of the TCRs from these T cells for the positively selecting ligand were extremely low and at least 10-fold less than those for the activating ligand. These results support the theory that positive selection is driven by TCR affinities lower than those involved in T cell deletion or activation and that, if present at high concentration, even very low affinity ligands can positively select.

Major histocompatibility complex (MHC) class I KbDb −/− deficient mice possess functional CD8+ T cells and natural killer cells

We obtained mice deficient for major histocompatibility complex (MHC) molecules encoded by the H-2K and H-2D genes. H-2 KbDb −/− mice express no detectable classical MHC class I-region associated (Ia) heavy chains, although β2-microglobulin and the nonclassical class Ib proteins examined are expressed normally. KbDb −/− mice have greatly reduced numbers of mature CD8+ T cells, indicating that selection of the vast majority (>90%) of CD8+ T cells cannot be compensated for by β2-microglobulin-associated molecules other than classical H-2K and D locus products. In accord with the greatly reduced number of CD8+ T cells, spleen cells from KbDb −/− mice do not generate cytotoxic responses in primary mixed-lymphocyte cultures against MHC-disparate (allogeneic) cells. However, in vivo priming of KbDb −/− mice with allogeneic cells resulted in strong CD8+ MHC class Ia-specific allogeneic responses. Thus, a minor population of functionally competent peripheral CD8+ T cells capable of strong cytotoxic activity arises in the complete absence of classical MHC class Ia molecules. KbDb −/− animals also have natural killer cells that retain their cytotoxic potential.

Major histocompatibility complex class I-restricted T cells are required for all but the end stages of diabetes development in nonobese diabetic mice and use a prevalent T cell receptor α chain gene rearrangement

Nonobese diabetic (NOD) mice develop insulin-dependent diabetes mellitus due to autoimmune T lymphocyte-mediated destruction of pancreatic β cells. Although both major histocompatibility complex class I-restricted CD8+ and class II-restricted CD4+ T cell subsets are required, the specific role each subset plays in the pathogenic process is still unclear. Here we show that class I-dependent T cells are required for all but the terminal stages of autoimmune diabetes development. To characterize the diabetogenic CD8+ T cells responsible, we isolated and propagated in vitro CD8+ T cells from the earliest insulitic lesions of NOD mice. They were cytotoxic to NOD islet cells, restricted to H-2Kd, and showed a diverse T cell receptor β chain repertoire. In contrast, their α chain repertoire was more restricted, with a recurrent amino acid sequence motif in the complementarity-determining region 3 loop and a prevalence of Vα17 family members frequently joined to the Jα42 gene segment. These results suggest that a number of the CD8+ T cells participating in the initial phase of autoimmune β cell destruction recognize a common structural component of Kd/peptide complexes on pancreatic β cells, possibly a single peptide.

Pig but not human interferon-γ initiates human cell-mediated rejection of pig tissue in vivo

Split-thickness pig skin was transplanted on severe combined immunodeficient mice so that pig dermal microvessels spontaneously inosculated with mouse microvessels and functioned to perfuse the grafts. Pig endothelial cells in the healed grafts constitutively expressed class I and class II major histocompatibility complex molecules. Major histocompatibility complex molecule expression could be further increased by intradermal injection of pig interferon-γ (IFN-γ) but not human IFN-γ or tumor necrosis factor. Grafts injected with pig IFN-γ also developed a sparse infiltrate of mouse neutrophils and eosinophils without evidence of injury. Introduction of human peripheral blood mononuclear cells into the animals by intraperitoneal inoculation resulted in sparse perivascular mononuclear cell infiltrates in the grafts confined to the pig dermis. Injection of pig skin grafts on mice that received human peripheral blood mononuclear cells with pig IFN-γ (but not human IFN-γ or heat-inactivated pig IFN-γ) induced human CD4+ and CD8+ T cells and macrophages to more extensivley infiltrate the pig skin grafts and injure pig dermal microvessels. These findings suggest that human T cell-mediated rejection of xenotransplanted pig organs may be prevented if cellular sources of pig interferon (e.g., passenger lymphocytes) are eliminated from the graft.

Two distinct proteolytic processes in the generation of a major histocompatibility complex class I-presented peptide

Although cellular proteins degraded by proteasomes are the source of most antigenic peptides presented on major histocompatibility complex class I molecules, it is unknown whether the eight- to nine-residue peptides that fit in the binding groove of class I molecules are directly produced by proteasomes alone in vivo. If the eight-residue peptide SIINFEKL from chicken ovalbumin is extended by one or several residues at its C terminus and microinjected into cells or expressed from a minigene, it is processed and presented on major histocompatibility complex class I. However, processing and presentation are inhibited by proteasome inhibitors, such as lactacystin. In contrast, when SIINFEKL is extended by 2 to 25 residues at its N terminus, its presentation is not blocked by proteasome inhibitors. N-terminal processing also can occur when the extended peptide is cotranslationally inserted into the endoplasmic reticulum. Thus, two different proteolytic steps in the generation of an chicken ovalbumin-presented peptide can be distinguished. Cleavage by the proteasome defines the proper C terminus, whereas distinct peptidase(s) in the cytosol or endoplasmic reticulum may generate the appropriate N terminus from extended peptides.

Interaction of pigeon cytochrome c-(43–58) peptide analogs with either T cell antigen receptor or I-Ab molecule

We determined that a pigeon cytochrome c-derived peptide, p43–58, possesses two anchor residues, 46 and 54, for binding with the I-Ab molecule that are compatible to the position 1 (P1) and position 9 (P9) of the core region in the major histocompatibility complex (MHC) class II binding peptides, respectively. In the present study to analyze each binding site between P1 and P9 of p43–58 to either I-Ab or T cell antigen receptor (TCR), we investigated T cell responses to a series of peptides (P2K, P3K, P4K, P5K, P6K, P7K, and P8E) that sequentially substituted charged amino acid residues for the residues at P2 to P8 of p43–58. T cells from C57BL/10 (I-Ab) mice immunized with P4K or P6K did not mount appreciable proliferative responses to the immunogens, but those primed with other peptides (P2K, P3K, P5K, P7K, and P8E) showed substantial responses in an immunogen-specific manner. It was demonstrated by binding studies that P1 and P9 functioned as main anchors and P4 and P6 functioned as secondary anchors to I-Ab. Analyses of Vβ usage of T cell lines specific for these analogs suggested that P8 interacts with the complementarity-determining region 1 (CDR1)/CDR2 of the TCR β chain. Furthermore, sequencing of the TCR on T cell hybridomas specific for these analogs indicated that P5 interacts with the CDR3 of the TCR β chain. The present findings are consistent with the three-dimensional structure of the trimolecular complex that has been reported for TCR/peptide/MHC class I molecules.

Targeting HIV proteins to the major histocompatibility complex class I processing pathway with a novel gp120-anthrax toxin fusion protein

A challenge for subunit vaccines whose goal is to elicit CD8+ cytotoxic T lymphocytes (CTLs) is to deliver the antigen to the cytosol of the living cell, where it can be processed for presentation by major histocompatibility complex (MHC) class I molecules. Several bacterial toxins have evolved to efficiently deliver catalytic protein moieties to the cytosol of eukaryotic cells. Anthrax lethal toxin consists of two distinct proteins that combine to form the active toxin. Protective antigen (PA) binds to cells and is instrumental in delivering lethal factor (LF) to the cell cytosol. To test whether the lethal factor protein could be exploited for delivery of exogenous proteins to the MHC class I processing pathway, we constructed a genetic fusion between the amino-terminal 254 aa of LF and the gp120 portion of the HIV-1 envelope protein. Cells treated with this fusion protein (LF254-gp120) in the presence of PA effectively processed gp120 and presented an epitope recognized by HIV-1 gp120 V3-specific CTL. In contrast, when cells were treated with the LF254-gp120 fusion protein and a mutant PA protein defective for translocation, the cells were not able to present the epitope and were not lysed by the specific CTL. The entry into the cytosol and dependence on the classical cytosolic MHC class I pathway were confirmed by showing that antigen presentation by PA + LF254-gp120 was blocked by the proteasome inhibitor lactacystin. These data demonstrate the ability of the LF amino-terminal fragment to deliver antigens to the MHC class I pathway and provide the basis for the development of novel T cell vaccines.

Efficient loading of HLA-DR with a T helper epitope by genetic exchange of CLIP

The HLA class II-associated invariant chain (Ii)-derived peptide (CLIP) occupies the peptide binding groove during assembly in the endoplasmic reticulum, travels with HLA class II to endosomal compartments, and is subsequently released to allow binding of antigenic peptides. We investigated whether the exchange of CLIP with a known T helper epitope at the DNA level would lead to efficient loading of this helper epitope onto HLA class II. For this purpose, a versatile Ii-encoding expression vector was created in which CLIP can be replaced with a helper epitope of choice. Upon supertransfection of HLA-DR1-transfected 293 cells with an Ii vector encoding a known T helper epitope (HA307–319), predominantly length variants of this epitope were detected in association with the HLA-DR1 molecules of these cells. Moreover, this transfectant was efficiently recognized by a peptide-specific T helper clone (HA1.7). The results suggest that this type of Ii vector can be used to create potent class II+ cellular vaccines in which defined T cell epitopes are continuously synthesized.

Extracellular antigen processing and presentation by immature dendritic cells

In antigen presentation to CD4+ T cells, proteins are degraded to peptide fragments and loaded onto class II MHC molecules in a process involving the peptide exchange factors H-2M (murine) or HLA-DM (human). In many antigen-presenting cells these processes occur in intracellular endosomal compartments, where peptides are generated and loaded onto class II MHC proteins for subsequent transport to the surface and presentation to T cells. Here, we provide evidence for an additional antigen-processing pathway in immature dendritic cells (DC). Immature DC express at the cell surface empty or peptide-receptive class II MHC molecules, as well as H-2M or HLA-DM. Secreted DC proteases act extracellularly to process intact proteins into antigenic peptides. Peptides produced by such activity are efficiently loaded onto cell surface class II MHC molecules. Together these elements comprise an unusual extracellular presentation pathway in which antigen processing and peptide loading can occur entirely outside of the cell.

Constitutive tyrosine phosphorylation of the inhibitory paired Ig-like receptor PIR-B

PIR-A and PIR-B are activating and inhibitory Ig-like receptors on murine B lymphocytes, dendritic cells, and myeloid-lineage cells. The inhibitory function of PIR-B is mediated via its cytoplasmic immunoreceptor tyrosine-based inhibitory motifs, whereas PIR-A pairs with the Fc receptor common γ chain to form an activating receptor complex. In these studies, we observed constitutive tyrosine phosphorylation of PIR-B molecules on macrophages and B lymphocytes, irrespective of the cell activation status. Splenocyte PIR-B molecules were constitutively associated with the SHP-1 protein tyrosine phosphatase and Lyn protein tyrosine kinase. In Lyn-deficient mice, PIR-B tyrosine phosphorylation was greatly reduced. Unexpectedly, tyrosine phosphorylation of PIR-B was not observed in most myeloid and B cell lines but could be induced by ligation of the PIR molecules. Finally, the phosphorylation status of PIR-B was significantly reduced in MHC class I-deficient mice, although not in mice deficient in TAP1 or MHC class II expression. These findings suggest a physiological inhibitory role for PIR-B that is regulated by endogenous MHC class I-like ligands.

Superactivation of an immune response triggered by oligomerized T cell epitopes

The peptides bound to class II major histocompatibility complex (MHC) molecules extend out both ends of the peptide binding groove. This structural feature provided the opportunity to design multivalent polypeptide chains that cross-link class II MHC molecules through multiple, repetitive MHC binding sites. By using recombinant techniques, polypeptide oligomers were constructed that consist of up to 32 copies of an HLA-DR1-restricted T cell epitope. The epitope HA306–318, derived from influenza virus hemagglutinin, was connected by 12- to 36-aa long spacer sequences. These oligomers were found to cross-link soluble HLA-DR1 molecules efficiently and, upon binding to the MHC molecules of a monocyte line, to trigger signal transduction indicated by the enhanced expression of some cell surface molecules. A particularly strong effect was evident in the T cell response. A hemagglutinin-specific T cell clone recognized these antigens at concentrations up to three to four orders of magnitude lower than that of the peptide or the hemagglutinin protein. Both signal transduction in the monocyte and the proliferative response of the T cell were affected greatly by the length of the oligomer (i.e., the number of repetitive units) and the distance of the epitopes within the oligomer (spacing). Thus, the formation of defined clusters of T cell receptor/MHC/peptide antigen complexes appears to be crucial for triggering the immune response and can be used to enhance the antigenicity of a peptide antigen by oligomerizing the epitope.

Inhibition of MHC class I-restricted antigen presentation by γ2-herpesviruses

The γ-herpesviruses, in contrast to the α- and β-herpesviruses, are not known to inhibit antigen presentation to CD8+ cytotoxic T lymphocytes (CTLs) during lytic cycle replication. However, murine γ-herpesvirus 68 causes a chronic lytic infection in CD4+ T cell-deficient mice despite the persistence of a substantial CTL response, suggesting that CTL evasion occurs. Here we show that, distinct from host protein synthesis shutoff, γ-herpesvirus 68 down-regulates surface MHC class I expression on lytically infected fibroblasts and inhibits their recognition by antigen-specific CTLs. The viral K3 gene, encoding a zinc-finger-containing protein, dramatically reduced the half-life of nascent class I molecules and the level of surface MHC class I expression and was by itself sufficient to block antigen presentation. The homologous K3 and K5 genes of the related Kaposi's sarcoma-associated virus also inhibited antigen presentation and decreased cell surface expression of HLA class I antigens. Thus it appears that an immune evasion strategy shared by at least two γ-herpesviruses allows continued lytic infection in the face of strong CTL immunity.