Ovine dendritic cells transduced with an adenoviral CTLA4eEGFP fusion protein construct induce hyporesponsiveness to allostimulation

Characterization of dendritic cells and follicular dendritic cells in the hepatic lymph nodes and liver of sheep experimentally infected with Fasciola hepatica

Fasciola hepatica has been shown to have a high capacity for immunomodulation of the host response, making the development of protective vaccines extremely difficult. One of these immunomodulation mechanisms is the impairment of dendritic cells (DC) maturation and, therefore, suppression of antigenic presentation. The aim of this study was to evaluate the pathological changes as well as the characterization of two antigen presenting cells, DC (CD1b, CD83 and MHC-II positive) and follicular dendritic cells (FDC) (CNA.42, S100 and CD83 positive) by immunohistochemistry in the hepatic lymph nodes (HLN) and livers of sheep during the early stages of infection with F. hepatica [9 and 18 days post-infection (dpi)], compared with an uninfected group (UC) as a control. The results revealed a marked hyperplasia of HLN germinal centres at 9 and, in particular, 18 dpi, with respect to the UC group, with coincidental increased expression of CNA.42 in FDC of lymphoid follicles and CD1b in the DC of paracortical areas at 18 dpi. However, the expression of MHC-II and CD83 decreased at 9 and, particularly, at 18 dpi in HLN compared with that in the UC group. Since both markers are related to active presentation of antigens by DC and FDC, the results of the present study suggest that, despite the marked hyperplasia of HLN and increase in DC and FDC numbers during early stages of infection, the DC and FDC antigenic presentation capacity, as suggested by the expression of the markers MHC-II and CD83, is suppressed by the parasite. This suppression was not observed in the liver, probably because of the low number of DC. This is the first study of the immunophenotype of DCs and FDC in sheep infected with F. hepatica.

Immunophenotyping of Sheep Paraffin-Embedded Peripheral Lymph Nodes

Sheep are not only a major livestock species globally, they are also an important large animal model for biomedical research and have contributed to our understanding of the ontogeny and architecture of the mammalian immune system. In this study, we applied immunohistochemistry and multicolor immunofluorescence in fixed and paraffin-embedded lymph nodes to phenotype the key populations of antigen presenting cells, lymphocytes, and stromal cells that orchestrate the host adaptive immune response. We used an extensive panel of antibodies directed against markers associated with dendritic cells (MHC class II, CD83, and CD208), macrophages (CD11b, CD163, and CD169), stromal cells (CNA.42, S100, and CD83), and lymphocytes (CD3, Pax5, CD4, CD8). Using different methods of tissue fixation and antigen retrieval, we provide a detailed immunophenotyping of sheep lymph nodes including the identification of potential subpopulations of antigen presenting cells and stromal cells. By characterizing cells expressing combinations of these markers in the context of their morphology and location within the lymph node architecture, we provide valuable new tools to investigate the structure, activation, and regulation of the sheep immune system in health and disease.

CTLA-4 is expressed by human monocyte-derived dendritic cells and regulates their functions

Cytotoxic T lymphocyte antigen-4 (CTLA-4) is the major negative regulator of T-cell responses, although growing evidence supports its wider role as an immune attenuator that may also act in other cell lineages. Here, we have analyzed the expression of CTLA-4 in human monocytes and monocyte-derived dendritic cells (DCs), and the effect of its engagement on cytokine production and T-cell stimulatory activity by mature DCs. CTLA-4 was highly expressed on freshly isolated monocytes, then down-modulated upon differentiation toward immature DCs (iDCs) and it was markedly upregulated on mature DCs obtained with different stimulations (lipopolysaccharides [LPS], Poly:IC, cytokines). In line with the functional role of CTLA-4 in T cells, treatment of mDCs with an agonistic anti-CTLA-4 mAb significantly enhanced secretion of regulatory interleukin (IL)-10 but reduced secretion of IL-8/IL-12 pro-inflammatory cytokines, as well as autologous CD4+ T-cell proliferation in response to stimulation with recall antigen purified protein derivative (PPD) loaded-DCs. Neutralization of IL-10 with an anti-IL-10 antibody during the mDCs-CD4+ T-cell co-culture partially restored the ability of anti-CTLA-4-treated mDCs to stimulate T-cell proliferation in response to PPD. Taken together, our data provide the first evidence that CTLA-4 receptor is expressed by human monocyte-derived mDCs upon their full activation and that it exerts immune modulatory effects.

Natural killer cells prime the responsiveness of autologous CD4+ T cells to CTLA4-Ig and interleukin-10 mediated inhibition in an allogeneic dendritic cell-mixed lymphocyte reaction

Cytotoxic T-lymphocyte antigen 4 immunoglobulin (CTLA4-Ig) and interleukin (IL)-10 are immunomodulatory molecules which target CD28 costimulation by acting either directly or indirectly on the CD80/86 receptors on dendritic cells (DCs). This study examined the effect of combined treatment with CTLA4-Ig and IL-10 on T-cell responsiveness in a dendritic cell-mixed lymphocyte reaction (DC-MLR). T cells derived from nylon wool enrichment (NWT cells) demonstrated 15% (P = 0.006) and 10% (P = 0.0015) inhibition of proliferation with suboptimal doses of IL-10 (5 ng/ml) and CTLA4-Ig (20 ng/ml), respectively. Combined treatment with both agents resulted in 38% inhibition (P = 0.004) of the MLR response compared with untreated controls. In contrast to NWT cells, which consisted of CD4+, CD8+ and CD56+ (NK) cells, purified CD4+ T cells were less responsive to immunomodulation by CTLA4-Ig and IL-10. Repletion of the CD4+ T cells with NK cells restored IL-10 and CTLA4-Ig mediated immunomodulation, suggesting a role for NK cells in the regulation of DC-T-cell interactions. The specific effect of NK cells on DC activation was demonstrated by CD80 up-regulation on DCs in the absence of T cells. However, in the absence of DCs, NK cells augmented the proliferation of autologous CD4+ T cells stimulated by anti-CD3 monoclonal antibody (mAb), which was blocked by CTLA4-Ig. It is proposed that, in the MLR, immunomodulation by suboptimal CTLA4-Ig and IL-10 is influenced by cellular interactions of NK cells with DCs and T cells involving DC lysis and costimulation. Thus, NK cells prime both DCs and T cells to low doses of CTLA4-Ig and IL-10 during alloimmune responses, providing evidence for the potential interaction between innate and adaptive immunity.

"Dendritic cells in different animal species: an overview"

The comprehension of the immune system and the role of DC in the pathological diseases may contribute to their use in veterinary medicine in the prevention and treatment of many diseases. Currently, most dendritic cell (DC) research occurs in the human and murine model systems on the generation of cells from the bone marrow or peripheral blood mononuclear cells (PBMC) cultured in vitro. Despite the lack of available immunological reagents such as antibodies and cytokines, analogous cells have been generated and identified in many different species and reviewed in this study.