MHC molecules in health and disease: At the cusp of a paradigm shift.

Half a century after the major histocompatibility complex (MHC) was discovered, its functional roles in health and disease remain poorly understood. Many hallmarks of the MHC, including its unusual evolution, structurefunction properties of its gene products and allele-specific associations with dozens of diseases and health traits cannot be convincingly explained by the tenets of existing paradigms. It is therefore becoming increasingly apparent that in order to better understand MHC-health/disease association-a phenomenon that impacts the health of millions-heterodox ideas are critically needed. Here we propose a testable, novel theory concerning the functional role of MHC molecules in health and disease. At the focus of this theory is an evolutionarily-conserved, tri-dimensional cusp-like prominence ('kink'), found in the midst of one of the two α helices that form the perimeter of the groove of all MHC molecules. Based on structural, functional and evolutionary considerations, as well as our recent experimental data, it is proposed here that the MHC cusp region is enriched in allele-specific signal transduction ligands that interact with non-MHC cell surface receptors and trigger signaling events. Aberrations in these pathways could lead to disease development, or affect the severity of such diseases.

Computed tomographic-dacryocystography (CT-DCG) of the normal canine nasolacrimal drainage system with three-dimensional reconstruction.

The aims of the study were (1) to quantify the influence of selected imaging parameters on the image quality (slice thickness, mAs, and beam orientation) defining optimal conditions for scan protocols and (2) to evaluate the benefits of the 3D reconstruction techniques for visualization of NDS structures in dogs. CT-DCG was performed bilaterally in 32 heads of dogs. CT transverse images were obtained using a combination of two slice thickness values (0.8 mm and 2 mm) and two mAs values (50 mAs and 300 mAs). Two beam projection orientations were also tested: transverse plane (perpendicular to the hard palate) and oblique to the hard palate. Three-dimensional images were obtained using Volume Rendering (VR). Transverse beam projection proved to be superior for the assessment of the inferior and superior lacrimal canaliculi and lacrimal sac. In this study, there was no statistical difference regarding mAs values (50 mAs and 300 mAs) and slice thickness values (0.8 mm and 2 mm). Three-dimensional images were helpful for the assessment of topographic relationship between nasolacrimal structures and cranial landmarks.

New insights into the functional role of the rheumatoid arthritis shared epitope.

The shared epitope (SE) - an HLA-DRB1-encoded 5-amino acid sequence motif carried by the vast majority of rheumatoid arthritis (RA) patients - is a risk factor for severe disease. The mechanistic basis of RA-SE association is unknown. This group has previously demonstrated that the SE acts as a signal transduction ligand that activates nitric oxide and reactive oxygen species production. SE-activated signaling depends on cell surface calreticulin, a known innate immunity receptor previously implicated in immune regulation, autoimmunity and angiogenesis. Recent evidence that the SE enhances the polarization of Th17 cells, which is a key mechanism in autoimmunity, is discussed highlighting one of several potential functional effects of the SE in RA.

A role for calreticulin in the pathogenesis of rheumatoid arthritis.

Calreticulin (CRT) plays a role in the clearance of dying cells and has been implicated in autoimmunity. Recent evidence indicates that cell surface CRT (csCRT) acts as a signal transducing receptor for the rheumatoid arthritis (RA) shared epitope (SE). The SE binding site on CRT has been mapped to amino acid residues 217-223 in the P-domain. Upon interaction with dendritic cells (DCs), the SE activates potent immune regulatory events. In CD8α(+) DCs, which express higher abundance of csCRT, the SE inhibits the tolerogenic enzyme indoleamine 2,3 dioxygenase with resultant inhibition of regulatory T (Treg) cell differentiation. In CD8α(-) DCs, the SE ligand increases secretion of IL-6 and IL-23 and facilitates generation of Th17 cells, a T cell subset known to play a role in autoimmunity. On the basis of these recent findings, we discuss the possibility that the csCRT may play a pathogenic role in RA by transducing SE-activated Th17-polarizing signals.

Immune dysregulation by the rheumatoid arthritis shared epitope.

Rheumatoid arthritis (RA) is closely associated with HLA-DRB1 alleles that code a five-amino acid sequence motif in positions 70-74 of the HLA-DRbeta-chain, called the shared epitope (SE). The mechanistic basis of SE-RA association is unknown. We recently found that the SE functions as an allele-specific signal-transducing ligand that activates an NO-mediated pathway in other cells. To better understand the role of the SE in the immune system, we examined its effect on T cell polarization in mice. In CD11c(+)CD8(+) dendritic cells (DCs), the SE inhibited the enzymatic activity of indoleamine 2,3 dioxygenase, a key enzyme in immune tolerance and T cell regulation, whereas in CD11c(+)CD8(-) DCs, the ligand activated robust production of IL-6. When SE-activated DCs were cocultured with CD4(+) T cells, the differentiation of Foxp3(+) T regulatory cells was suppressed, whereas Th17 cells were expanded. The polarizing effects could be seen with SE(+) synthetic peptides, but even more so when the SE was in its natural tridimensional conformation as part of HLA-DR tetrameric proteins. In vivo administration of the SE ligand resulted in a greater abundance of Th17 cells in the draining lymph nodes and increased IL-17 production by splenocytes. Thus, we conclude that the SE acts as a potent immune-stimulatory ligand that can polarize T cell differentiation toward Th17 cells, a T cell subset that was recently implicated in the pathogenesis of autoimmune diseases, including RA.

Ultrassonografia em modo A e B na avaliação pré-operatória da lente e do segmento posterior de olhos de cães com catarata / A and B mode ultrasonography in preoperative evaluation of lens and posterior segment of dogs eyes with cataract

Ultrasonography of the lens and posterior segment is an indispensable step in the preoperative evaluation of dogs with cataracts, since ophthalmoscopy is not feasible when there is opacification of the lens. This study evaluated the echographic conditions of cataractous lens and fundus of the eye in dogs affected by cataracts. The study was conducted in 30 dogs (56 eyes), 10 males and 20 females, with different types of cataracts at different stages of development. Echography in A and B modes, simultaneously, was carried out for the examination of the lens and posterior segment. The examinations revealed anterior cortical, posterior cortical and nuclear cataract in 12 eyes (21.4 percent), anterior cortical, posterior cortical, nuclear and posterior capsular in 23 eyes (41 percent), anterior cortical, posterior cortical and posterior capsular cataract in one eye (1.7 percent), anterior cortical and nuclear cataract in one eye (1.7 percent), anterior cortical, nuclear and posterior capsular cataract in five eyes (8.9 percent), and anterior cortical cataract in seven eyes (12.5 percent). Abnormal ultrasonographic alterations were observed in the posterior segment in 26 eyes evaluated (46.4 percent). Vitreal degeneration was detected in 12 eyes (21.4 percent), images of vitreal exudate or hemorrhage in seven eyes (12.5 percent), persistence of hyaloid artery in four eyes (7.1 percent) and lens subluxation in three eyes (5.3 percent). The results obtained reiterate the importance of ultrasonography in canine patients presented for cataract surgery given that alterations of the posterior segment are difficult to identify in a clinical examination when the lens is opacified.

A ultrassonografia do segmento posterior do bulbo do olho é etapa indispensável na avaliação de cães com catarata que serão submetidos à facectomia, uma vez que a oftalmoscopia não é factível quando há opacificação da lente, notadamente nas cataratas maduras. Este estudo avaliou as condições ecográficas da lente cataratogênica e do fundo de olho de cães cursando com catarata. Foram avaliados 30 cães (56 olhos), sendo 10 machos e 20 fêmeas, cursando com catarata em diferentes estágios de desenvolvimento. Realizou-se a ecografia em modo A e B simultaneamente. Os exames revelaram catarata cortical anterior, posterior e nuclear em 12 olhos (21,4 por cento), catarata cortical anterior, posterior, nuclear e capsular posterior em 23 olhos (41 por cento), catarata cortical anterior, posterior e capsular posterior em um olho (1,7 por cento), catarata cortical anterior e nuclear em um olho (1,7 por cento), catarata cortical anterior, nuclear e capsular posterior em cinco olhos (8,9 por cento) e catarata cortical anterior em sete olhos (12,5 por cento). Alterações no segmento posterior foram observadas, à ultrassonografia, em 26 olhos avaliados (46,4 por cento). Degeneração vítrea foi detectada em 12 olhos (21,4 por cento), imagens compatíveis com exsudato ou hemorragia em sete olhos (12,5 por cento), persistência da artéria hialóide em quatro olhos (7,1 por cento) e subluxação da lente em três olhos (5,3 por cento). Os resultados obtidos reiteram a importância da ultrassonografia em cães candidatos à cirurgia de catarata, uma vez que o exame do segmento posterior do bulbo do olho é de difícil execução, devido à opacificação da lente.

Antigen-specific regulatory T cells in bovine paratuberculosis.

Mycobacterium avium subspecies paratuberculosis (MAP) is an intracellular pathogen that survives in the host's intestinal macrophages and causes chronic enteritis in ruminants. The subclinical stage of MAP infection is accompanied by loss of pro-inflammatory T(H)1 response, and a predominant, but ineffective, antibody-mediated T(H)2 response. How MAP interacts with the bovine immune system and suppresses T(H)1 responses is unclear. Studies carried out in our lab and others indicate that when peripheral blood mononuclear cells (PBMCs) from subclinical MAP-infected cattle are stimulated with MAP-antigen, IL-10 is up-regulated and leads to suppression of IFN-gamma expression in MAP-antigen-reactive effector T cells. IL-10 up-regulation and reduction in IFN-gamma would favor MAP survival and proliferation in macrophages. Depletion studies in PBMCs from MAP-infected cattle also revealed that the MAP responsive T-cell population that produces IL-10 is CD4(+) and CD25(+). Therefore, we hypothesize that cattle infected with MAP develop regulatory T (Treg) cells capable of producing IL-10 that in turn limits peripheral and tissue-specific T(H)1 immune responses. The aim of this review is to summarize current thinking regarding Treg cells and provide preliminary evidence that infection of cattle with MAP may lead to development of Treg cells.

Effects of nitrous oxide on IOP and pupillary diameter in dogs anesthetized with varying concentrations of desflurane.

OBJECTIVE: The aim of the present study was to evaluate the effects of nitrous oxide on IOP and pupillary diameter (PD) of dogs anesthetized with varying desflurane concentrations. ANIMALS STUDIED: Twenty adult Mongrel dogs were used. METHODS: They were anesthetized with propofol (10 mg/kg, IV) and maintained with varying concentrations of desflurane (1.6, 1.4, and 1.2 MAC) diluted in 100% oxygen (G1) or in 70% nitrous oxide and 30% oxygen (G2) (30 mL/kg/min). IOP was measured by applanation tonometry and horizontal PD was taken with a caliper adjacent to the cornea. Mean arterial pressure (MAP), heart rate (HR), respiratory rate (RR), and end-tidal CO(2) (etCO2) were also measured. All parameters were measured at T0, T30, T45, and T60 time points. One-way repeated measures anova and the t-test were used to assess statistical differences (P < 0.05). RESULTS: T30, T45, and T60 IOP measures were within normal limits for both groups and IOP did not differ between groups at any time. There was a significant decrease in PD in G1 between T0 and T30, T45 and T60, and also between T30 and T60. PD did not differ between groups. All vital parameters were within normal limits throughout anesthesia. CONCLUSIONS: Administration of nitrous oxide with desflurane results in maintenance of normal IOP and prevents a decrease in horizontal PD during anesthesia. Therefore, this may be a suitable protocol in dogs undergoing intraocular surgeries that require mydriasis and maintenance of normal IOP.

Ophthalmic patterns of captive brown brocket deer (Mazama gouazoubira).

Captive brown brocket deer (Mazama gouazoubira) were manually restrained to assess tear production by the Schirmer tear test I to measure intraocular pressure by applanation tonometry, to examine ocular conjunctival epithelial cells via cytologic and histologic samples, and to survey ocular conjunctival microflora by microbiologic culture. The mean value for the Schirmer tear test I was 8.9 +/- 1.8 mm/min, and the mean intraocular pressure was 15.3 +/- 3.1 mm Hg. Conjunctival epithelium contained stratified pavimentous layers of cells, and the microflora consisted of predominantly gram-positive bacteria.