Patterns of major histocompatibility complex class II expression by T cell subsets in different immunological compartments. 2. Altered expression and cell function following activation in vivo

Pathways and Genes Associated with Immune Dysfunction in Sheep Paratuberculosis

Multibacillary and paucibacillary paratuberculosis are both caused by Mycobacterium avium subspecies paratuberculosis. Multibacillary lesions are composed largely of infected epithelioid macrophages and paucibacillary lesions contain T cells but few bacteria. Multibacillary disease is similar to human lepromatous leprosy, with variable/high levels of antibody and a dysfunctional immune response. Animals with paucibacillary disease have high cell-mediated immunity and variable levels of antibody. This study aims to characterize the immunological dysfunction using TruSeq analysis of the ileocaecal lymph node that drains disease lesions. Immune dysfunction is highlighted by repression of TCR/CD3 genes, T cell co-receptors/co-stimulators, T cell activation and signal-transduction genes. Inflammation was an acute phase response and chronic inflammation, with little evidence of acute inflammation. The high levels of immunoglobulin and plasma cell transcripts is consistent with the anti-MAP antibody responses in paratuberculosis sheep. Also notable was the overwhelming reduction in mast cell transcripts, potentially affecting DC activation of the immune response. This study also shows that there were no fundamental differences in the gene expression patterns in multibacillary and paucibacillary disease, no shift in T cell genes from Th1 to Th2 pattern but rather an incremental decline into immune dysfunction leading to multibacillary pathology.

The effect of PrP(Sc) accumulation on inflammatory gene expression within sheep peripheral lymphoid tissue

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Arrays quantified gene expression in peripheral LNs during sheep scrapie.

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Disease progression associated with alterations of inflammatory gene expression.

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Lymph node response contrasts with response of CNS.

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Step changes to gene expression after the detection of PrP^Sc in peripheral LNs.

Accumulation of the misfolded prion protein, PrP^Sc in the central nervous system (CNS) is strongly linked to progressive neurodegenerative disease. For many transmissible spongiform encephalopathies (TSEs), peripheral lymphoid tissue is an important site of PrP^Sc amplification but without gross immunological consequence. Susceptible VRQ homozygous New Zealand Cheviot sheep were infected with SSBP/1 scrapie by inoculation in the drainage area of the prescapular lymph nodes. The earliest time that PrP^Sc was consistently detected by immunohistology in these nodes was D50 post infection. This transcriptomic study of lymph node taken before (D10) and after (D50) the detection of PrP^Sc, aimed to identify the genes and physiological pathways affected by disease progression within the nodes as assessed by PrP^Sc detection. Affymetrix Ovine Gene arrays identified 75 and 80 genes as differentially-expressed at D10 and D50, respectively, in comparison with control sheep inoculated with uninfected brain homogenate. Approximately 70% of these were repressed at each time point. RT-qPCR analysis of seven genes showed statistically significant correlation with the array data, although the results for IL1RN and TGIF were different between the two technologies. The ingenuity pathway analysis (IPA) and general low level of repression of gene expression in lymphoid tissue, including many inflammatory genes, contrasts with the pro-inflammatory and pro-apoptotic events that occur within the CNS at equivalent stages of disease progression as assessed by PrP^Sc accumulation.

Ovine skin-recirculating γδ T cells express IFN-γ and IL-17 and exit tissue independently of CCR7

γδ T cells continuously survey extralymphoid tissues, providing key effector functions during infection and inflammation. Despite their importance, the function and the molecules that drive migration of skin-recirculating γδ T cells are poorly described. Here we found that γδ T cells traveling in the skin-draining afferent lymph of sheep are effectors that produce IFN-γ or IL-17 and express high levels of the skin- and inflammation-seeking molecule E-selectin ligand. Consistent with a role for chemokine receptor CCR7 in mediating T cell exit from extralymphoid tissues, conventional CD4 and CD8T cells in skin-draining lymph were enriched in their expression of CCR7 compared to their skin-residing counterparts. In contrast, co-isolated γδ T cells in skin or lymph lacked expression of CCR7, indicating that they use alternative receptors for egress. Skin-draining γδ T cells were unresponsive to many cutaneous and inflammatory chemokines, including ligands for CCR2, CCR4, CCR5, CCR8, CCR10, and CXCR3, but showed selective chemotaxis toward the cutaneously expressed CCR6 ligand CCL20. Moreover, IL-17(+) γδ T cells were the most CCL20-responsive subset of γδ T cells. The data suggest that γδ T cells survey the skin and sites of inflammation and infection, entering via CCR6 and E-selectin ligand and leaving independent of the CCR7-CCL21 axis.

Differential expression of pattern recognition receptors in sheep tissues and leukocyte subsets

The various members of the different pattern recognition receptor families are now recognized as playing a crucial role in the initial interactions between a pathogen and the host. This paper identifies all 10 members of the TLR family in sheep as well as key members of the C-type lectin and NLR families. Our data show that sheep possess the 'human' and not the 'mouse' pattern of TLRs and confirm the high degree of sequence identity between orthologous genes in the different species. In the absence of definitive antibodies, qRT-PCR assays were developed to quantify PRR transcript expression patterns in a range of normal sheep tissues as well as isolated dendritic cell (DC) and leukocyte subsets. These data show that the lymphoid organs (spleen and lymph nodes) express the widest range of PRRs and that organs such as the lung and kidney have distinctive arrays of PRRs that reflect their potential risk of pathogen exposure. In addition we show that the two DC subsets, defined by the differential expression of CD172a/CD45RA and their cytokine expression profiles, have different and characteristic PRR complements again possibly reflecting their distinctive function. These data are important for future studies on the role of PRRs in disease pathogenesis and control.

Role of lymph-borne cells in the early stages of scrapie agent dissemination from the skin

Scrapie is a natural transmissible spongiform encephalopathy (TSE) of sheep, infecting the animal via the gastrointestinal tract or the skin. This project tested the hypotheses that lymph-borne cells (especially dendritic cells) are crucial for the systemic dissemination of the infectious agent from the site of infection in the skin, that PrP genotype affects PrPSC association with dendritic cells and that PrPSC carriage by cells affects their expression of cytokines. Skin, of scrapie-susceptible VRQ/ARR and scrapie-resistant ARR/ARR PrP genotypes, was scarified with FITC-labelled PrPSC. Pseudoafferent lymphatic cannulation was then used to monitor the presence of FITC-PrPSC over time in different lymph cell populations and plasma in the draining afferent lymphatics. The major observation was that PrPSC did not associate significantly with any lymphocyte or dendritic cell population in the 5 days following PrPSC scarification. The only cells seen to associate with PrPSC were neutrophils. Furthermore, despite the quantity of PrPSC used for scarification being equivalent to a standard infectious dose (the VRQ/ARR sheep dying at approximately 260 days) the only PrP found in afferent lymph during the 0-5-day period was proteinase K sensitive (i.e. soluble PrPC). No differences were observed between the PrP genotypes. Analysis of the effects of PrPSC scarification of cellular cytokine mRNA expression (by a nuclease protection assay) showed raised levels of IL-1beta and IL-8 in the susceptible VRQ/ARR group and raised levels of IFNgamma in the resistant ARR/ARR animals.

Serial analysis of gene expression in circulating gamma delta T cell subsets defines distinct immunoregulatory phenotypes and unexpected gene expression profiles

Gene expression profiles were compared in circulating bovine GD3.5+ (CD8-) and GD3.5- (predominantly CD8+) gammadelta T cells using serial analysis of gene expression (SAGE). Approximately 20,000 SAGE tags were generated from each library. A comparison of the two libraries demonstrated 297 and 173 tags representing genes with 5-fold differential expression in GD3.5+ and GD3.5- gammadelta T cells, respectively. Consistent with their localization into sites of inflammation, GD3.5+ gammadelta T cells appeared transcriptionally and translationally more active than GD3.5- gammadelta cells. GD3.5- gammadelta T cells demonstrated higher expression of the cell proliferation inhibitor BAP 37, which was associated with their less activated gene expression phenotype. The immune regulatory and apoptosis-inducing molecule, galectin-1, was identified as a highly abundant molecule and was higher in GD3.5+gammadelta T cells. Surface molecules attributed to myeloid cells, such as CD14, CD68, and scavenger receptor-1, were identified in both populations. Furthermore, expression of B lymphocyte-induced maturation protein, a master regulator of B cell and myeloid cell differentiation, was identified by SAGE analysis and was confirmed at the RNA level to be selectively expressed in gammadelta T cells vs alphabeta T cells. These results provide new insights into the inherent differences between circulating gammadelta T cell subsets.

Acquisition of functional MHC class II/peptide complexes by T cells during thymic development and CNS-directed pathogenesis

This study provides evidence that both rat and mouse thymic and splenic T cells express significant levels of MHC class II glycoproteins (MHCII) in vivo. Derivation of rat and mouse chimeras revealed that a major source of MHCII on thymic T cells was acquired from radioresistant host APC. Expression of MHC on thymic T cells appeared physiologically relevant because presentation of rat myelin basic protein (RMBP) by nonadherent, radiosensitive thymic T cells was associated with the adoptive transfer of tolerance. Mature MBP-specific effector T cells isolated from the CNS in both rat and mouse models of EAE also expressed significant levels of MHCII. Adoptive transfer of activated B10.PL MBP/I-A(u)-restricted TCR transgenic T cells into F1(C57BL/6 x B10.PL) mice revealed acquisition of allogeneic I-A(b) on encephalitogenic CNS-derived T cells. Overall, this study indicates that immature and mature T cells in rats and mice acquire functional MHCII in vivo during thymic development and pathogenic inflammation.

Natural and induced regulation of Th1/Th2 balance

Because Th1/Th2 balance is perturbed during immunological disease, the design of strategies aiming at its rectification has become a priority. The alteration of the balance in pregnancy so as to promote survival of the fetal allograft lends credibility to this aim. Attenuation of the activation signal delivered through the T cell receptor (TCR) represents a promising approach. It is supported by the high level of polymorphism in the MHC class II promoter, which regulates the natural TCR signal and thus modulates Th1/Th2 differentiation. Further support comes from the Th2 shift that occurs in JNK knockout mice, and with kinase inhibitors and anti-CD4 monoclonal antibodies applied in vitro. The approach has implications for nasal tolerance and inhibition of IL-12 production. The further range of options for Th1/Th2 modulation, which are presented throughout this issue of the journal, are here summarised and evaluated.

Early immunopathological events in experimental ovine paratuberculosis

An experimental oral infection of neonatal (< 2 weeks old) lambs with a cervine isolate of Mycobacterium avium subspecies paratuberculosis (M.a. paratuberculosis), the causal agent of ruminant paratuberculosis (Johne's disease) was used to investigate bacteriological, histopathological and immunological changes during the early (up to 8 weeks) post-infection phase. In vitro culture for mycobacteria was positive in one faecal and three mesenteric lymph node (MLN) samples from the eight infected lambs. All mycobacterial isolates from MLN were identified as M.a. paratuberculosis by polymerase chain reaction (PCR). Small-to-medium sized focal granulomata were observed in jejunal (JPP) and ileal Peyer's patches (IPP) from four of the eight infected lambs. Compared with controls, JPP from all infected lambs had significantly (p < 0.05) higher proportions of CD8+ and CD2+ lymphocytes, and there were significantly (p < 0.05) fewer cells expressing B lymphocyte-associated markers in IPP and MLN. The T/B cell ratio was significantly (p < 0.05) increased in both JPP and MLN from infected lambs. The expression of a range of genes for cytokines was examined using specific reverse transcriptase PCR (RT-PCR) amplification of messenger RNA (mRNA) template isolated from MLN, JPP and IPP from both groups of animals. Densitometric analyses indicated that, in infected animals, MLN expressed significantly (p < 0.05) more mRNA for TNF-alpha: JPP had significantly increased (p < 0.05) mRNA for GM-CSF and significantly decreased (p < 0.05) mRNA for IL-4 and IFN-gamma. Infected lambs had significantly (p < 0.05) decreased titres of both circulating IgG and gut mycobacteria-associated IgG antibody. Infection was not associated with any consistent changes in lymphocyte reactivity to specific mycobacterial antigens, IFN-gamma release into supernatants from in vitro intestinal lymphocyte cultures or gut IgA antibody levels.

Compartments within the lymph node cortex of calves and adult cattle differ in the distribution of leukocyte populations: an immunohistochemical study using computer-assisted morphometric analysis

The combination of an immunohistochemical technique and a panel of monoclonal antibodies was used to investigate the presence of leukocyte populations in the distal jejunal lymph node of 3-4 week old calves and adult cattle. The application of computer-assisted morphometric analysis enabled information to be obtained on the distribution of leukocyte populations in lymphoid compartments of the lymph node cortex. Semi-quantitative estimates of the areas of staining in histological sections showed that calves possessed significantly fewer B-cells and CD4+ cells in the outer cortex and significantly fewer T-cells (CD4+, CD8+ and gamma delta T-cells) in the deep cortex. These findings were interpreted to be a possible consequence of immunosuppression resulting from the passive transfer of maternal immunity in colostrum. The presence of some B-cell follicles in the region defined as the deep cortex suggested the on-going differentiation of this predominantly T-cell compartment. The larger presence of interdigitating cells (IDC) in the deep cortex of calves than adults was suggested by significantly larger CD1+ populations and it was argued that this could be the result of the confrontation with exogenous antigen faced by calves in early postnatal life. Antigen presenting populations, pan MHC II+ and MHC II DQ+ populations, were increased in all compartments of calf lymph nodes but were not significantly different from the populations in adult lymph nodes. Variance component analysis of the data generated in the present study showed that the image analysis technique was an effective and statistically powerful approach to investigate leukocyte populations within the specific microenvironments of the lymph node.

Cytotoxic T-lymphocyte responses in cattle infected with bovine viral diarrhea virus

A system for a reproducible in vitro restimulation of bovine viral diarrhea virus (BVDV)-specific cytotoxic T-cells (CTL) was developed. Lymphocyte cultures of BVDV-immunised cattle were stimulated with infectious BVDV isolate PT810 and recombinant bovine interleukin-2 for 12 to 25 days. A specific lysis of Concanavalin A-stimulated BVDV-infected autologous target cells was observed, whereas allogeneic BVDV-infected target cells were only marginally lysed as detected by flow cytometry. BVDV-specific lymphocyte transformation was further characterised by the expression of bovine lymphocyte activation antigens and bovine MHC class-II molecules. Secondary stimulation of CTL was influenced by in vitro production of BVDV-specific neutralising antibodies, which were secreted exclusively in BVDV-inoculated lymphocyte cultures of immunised cattle. These results demonstrate the presence of CTL in peripheral blood mononuclear cells (PBMC) of immunised cattle which can kill autologous BVDV-infected antigen-presenting cells after in vitro restimulation.

A study on lymphocyte activation in maedi-visna virus induced pneumonia

The stage of activation of bronchoalveolar lavage fluid (BALF) lymphocytes and peripheral blood lymphocytes (PBL) from maedi-visna virus (MVV) infected (n = 7) and control (n = 7) sheep was investigated by assessing four parameters of lymphocyte activation; lymphocyte size and complexity, loss of CD5+ T cells, expression of cell surface interleukin-2 receptor (IL-2R) and expression of DR and DQ MHC Class II molecules. BALF lymphocytes from MVV-infected animals had a significant loss of CD5+ lymphocytes (P < 0.05) and upregulation of DR and DQ MHC Class II molecules compared with controls, consistent with BALF lymphocyte activation. No changes in cell size and complexity or expression of IL-2R were observed. No evidence of PBL activation was detected. These findings suggest an impaired BALF lymphocyte activation during MVV infection.

Expression of major histocompatibility complex class II molecules in rat T cells

The expression of major histocompatibility complex (MHC) class II molecules in murine T cells has been controversial. We therefore reexamined the transcription, synthesis and surface expression of MHC class II determinants in rat T cells both in vivo and in vitro. In naive rats, a large proportion of small CD4+8+ and mature CD4+8-/CD4-8+ thymocytes was found to be MHC class II positive. At least some of the MHC class II molecules found on thymocytes were actively synthesized. The synthesis of MHC class II proteins was detected in peripheral T cells activated in vivo during induction of experimental allergic encephalomyelitis (EAE). A proportion of T cells from the inflammatory lesion of EAE exhibited MHC class II on the surface. A panel of helper T cell lines and clones was shown to synthesize MHC class II proteins. In a prototypic clone, a weak constitutive expression of MHC class II was observed. During activation, the rate of endogenous MHC class II synthesis increased and passive absorption of surface MHC class II from other cells occurred. Our data demonstrate the expression of MHC class II molecules in rat T cells in both the thymus and periphery. Since the primary function of MHC class II molecules is the presentation of peptide epitopes to T cells, these results call attention to the possible role of MHC class II molecules in T-T interactions during T cell maturation and activation.

Ovine lentivirus (maedi-visna virus) protein expression in sheep alveolar macrophages

The expression of gag (p15, p25) and env gene products in ovine lentivirus-infected cells was studied in 20 adult Texel ewes seropositive to maedi-visna virus and 10 seronegative matched controls. Bronchoalveolar lavage was performed to recover alveolar cell pools from which cytocentrifuge preparations were made. Single and double immunocytochemical techniques were applied to study viral replication and coexpression of viral markers with markers for macrophages, lymphocytes, and major histocompatibility complex (MHC) class II. Aveolar macrophages of eight of 20 infected sheep (40%) were positive for viral protein expression. The percentage of positive macrophages varied from < 1% to 12% of the total population of macrophages. Viral protein expression was not detected in lymphocytes or other cell types. A relationship between virus-replicating macrophages and differential expression of MHC class II molecules, upregulated in ovine lentivirus infection, could not be established. Pathology was evaluated in nine infected ewes. Animals with the highest levels of positive cells had moderate or severe lymphoid interstitial pneumonia. However, sheep with similar degrees of lesions had lower percentages of positive macrophages or were negative for viral protein detection. These results support the idea that a partial or even a complete loss in the restriction mechanism of maedi-visna virus in lungs can occur in some individuals.

Patterns of major histocompatibility complex class II expression on T cell subsets in different immunological compartments. 1. Expression on resting T cells

In this study we have investigated the expression of major histocompatibility complex (MHC) class II molecules on T cells from various lymphoid compartments in the sheep. Monoclonal antibodies which react specifically with sheep MHC class II molecules homologous to the human DQ and DR molecules have been characterized. These antibodies have been used, together with the monoclonal antibodies specific for sheep CD4-, CD8- and T19-positive T cells, to quantitate DQ and DR expression on T cell subsets in adult and fetal peripheral blood, afferent lymph, lymph node and efferent lymph. The results show that expression of class II by T cells depends on the age of the animal and the physiological location of the T cell. In fetal blood there is no expression of class II on CD8+ or T19+ cells and very low expression on CD4+ T cells. In adult peripheral blood and efferent lymph a significant proportion of cells express DR but not DQ. A very different situation is found in afferent lymph and the peripheral lymph node: in afferent lymph the majority of T cells in all three subsets express both DQ and DR molecules; in the lymph node over 50% of T cells express DR and 30% are DQ+. These results suggest that within all T cell subsets there is a progression from DQ-DR- to DQ-DR+ and DQ+DR+ which correlates with physiological stages of T cell differentiation in vivo.