Homeostasis of intestinal immune regulation

Regulatory CD4 T cells with the capacity to inhibit potentially harmful immune responses have been described in various experimental systems. Although the observations are converging towards the naturally activated CD25(+) CD4 T cells as a major population responsible for this protection, there is still considerable disagreement on the molecular and cellular requirements involved to achieve a stable immune homeostasis in vivo.     

Dendritic cells and cytokines in immune rejection of cancer

Dendritic cells (DCs) play a crucial role in linking innate and adaptive immunity and, thus, in the generation of a protective immune response against both infectious diseases and tumors. The ability of DCs to prime and expand an immune response is regulated by signals acting through soluble mediators, mainly cytokines and chemokines. Understanding how cytokines influence DC functions and orchestrate the interactions of DCs with other immune cells is strictly instrumental to the progress in cancer immunotherapy. Herein, we will illustrate how certain cytokines and immune stimulating molecules can induce and sustain the antitumor immune response by acting on DCs. We will also discuss these cytokine-DC interactions in the light of clinical results in cancer patients.     

Dendritic cells in colorectal cancer correlate with other tumor-infiltrating immune cells

Dendritic cells (DCs) are the most efficient antigen-presenting cells and play a key role in a cellular antitumor immune response. In this study we investigated the exact localization of DCs within colorectal tumors and their relationship to tumor-infiltrating lymphocytes as well as clinical outcome of the patients. Primary tumor specimens of 104 patients with a diagnosis of colorectal cancer were identified retrospectively and analyzed with the dendritic cell markers S-100 protein and human leukocyte antigens (HLA) class II. The markers were individually combined with laminin as a second marker to facilitate the observation of the different tumor localizations. S-100 or HLA class II positive cells were found in the three different compartments of colorectal tumors: tumor epithelium, tumor stroma, and advancing tumor margin, but mainly present in tumor stroma and advancing tumor margin. S-100-positive tumor-infiltrating DCs in direct contact with tumor cells, i.e., in tumor epithelium, significantly correlated to the intraepithelial infiltration of CD4+ (p=0.02) and CD8+ (p=0.01) lymphocytes. High HLA class II+ cell infiltration in the tumor stroma correlated to a lower intraepithelial infiltration of CD8+ (p=0.02) lymphocytes. High intraepithelial infiltration of S-100-positive DCs suggested increased disease-free survival, but was not statistically significant, while high amounts of HLA class II+ cells in the tumor stroma correlated with an adverse survival outcome. Our results show that the infiltration of DCs in colorectal cancer, depending on both location and type of marker, is correlated with local immune interactions and patient prognosis, suggesting a central role for DCs in controlling local tumor immunity.     

Dendritic cells and their role in immune reactions of atherosclerosis

Dendritic cells were discovered and recognized as antigen-presenting cells in 1973. Since then, a large volume of information has been accumulated showing the role of dendritic cells as a key element connecting the innate and adaptive immunity. Today, dendritic cells are considered to be dedicated sensors of the immune system that are capable of recognizing both antigen amounts and antigen persistence via complex mechanisms that involve decoding and integration of various signals received in a receptor-dependant manner. The tissue microenvironment plays an important role in the modulation of effector functions of dendritic cells, inducing either activation or suppression of immune reactions. Dendritic cells maintain homeostasis and are involved in a number of diseases, including infectious diseases and cancer. The presence of dendritic cells in arteries was reported in 1995, and, since then, the involvement of dendritic cells in atherogenesis has been evaluated. This review briefly describes the current knowledge of dendritic cells and their role in atherosclerosis.     

Dendritic cells amplify T cell-mediated immune responses in the central nervous system

Neuroinflammation often starts with the invasion of T lymphocytes into the CNS leading to recruitment of macrophages and amplification of inflammation. In this study, we show that dendritic cells (DCs) facilitate T-T cell help in the CNS and contribute to the amplification of local neuroinflammation. We adoptively transferred defined amounts of naive TCR-transgenic (TCR) recombination-activating gene-1-deficient T cells into another TCR-transgenic mouse strain expressing different Ag specificity. Following adoptive transfers, we coinjected DCs that presented one or multiple Ags into the brain and followed the activation of T cells with defined specificities simultaneously. Injection of DCs presenting both Ags simultaneously led to significantly higher infiltration of T cells into the brain compared with injection of a mixture of DCs pulsed with two Ags separately. DCs mediated either cooperative or competitive interactions between T cell populations with different specificities depending upon their MHC-restricting element usage. These results suggest that DC-mediated cooperation between brain-infiltrating T cells of different Ag specificities in the CNS plays an important role in regulation of neuroinflammation. This work also implies that blocking Ag-specific responses may block not only the targeted specificities, but may also effectively block their cooperative assistance to other T cells. Therefore, these data justify more attention to Ag-specific therapeutic approaches for neuroinflammation.     

肠粘膜上皮细胞在天然免疫中的作用

粘膜免疫是机体防御系统的主要成分。致病性细菌侵入机体后,首先遭遇到天然免疫的抵抗,随后产生获得性免疫,两共同执行机体的防御功能,消灭入侵细菌。最近的研究表明上皮细胞对细菌感染有重要的免疫调节作用,在天然免疫与获得性免疫防御机制中起重要作用。本重点介绍肠上皮细胞在天然免疫中的作用。     

Dendritic cells in the induction of protective and nonprotective anticryptococcal cell-mediated immune responses

Dendritic cells (DC) can be divided into three subsets, Langerhans cells, myeloid DC (MDC), and lymphoid DC (LDC), based upon phenotypic and functional differences. We hypothesized that different DC subsets are associated with the development of protective vs nonprotective cell-mediated immune (CMI) responses against the fungal pathogen, Cryptococcus neoformans. To test this, mice were immunized with protective and/or nonprotective immunogens, and DC subsets in draining lymph nodes were assessed by flow cytometry. The protective immunogen (cryptococcal culture filtrate Ag-CFA), in contrast to the nonprotective immunogen (heat-killed cryptococci-CFA), the nonprotective immunogen mixed with the protective immunogen (cryptococcal culture filtrate Ag + heat-killed cryptococci-CFA), or controls, stimulated significant increases in total leukocytes, Langerhans cells, MDC, LDC, and activated CD4+ T cells in draining lymph nodes. The protective immune response resulted in significantly increased levels of anticryptococcal delayed-type hypersensitivity reactivity and activated CD4+ T cells at the delayed-type hypersensitivity reaction site. Draining lymph node LDC:MDC ratios induced by the protective immunogen were significantly lower than the ratios induced by either immunization in which the nonprotective immunogen was present. In contrast, mice given the nonprotective immunogen had LDC:MDC ratios similar to those of naive mice. Our data indicate that lymph node Langerhans cells and MDC are APC needed for induction of the protective response. The predominance of LDC in mice undergoing nonprotective responses suggests that lymph node LDC, like splenic LDC, are negative regulators of CMI responses. In addition to showing DC subsets associated with functional differences, our data suggest that the LDC:MDC balance, which can be modulated by the Ag, determines whether protective or nonprotective anticryptococcal CMI responses develop.     

Dendritic cells capture killed tumor cells and present their antigens to elicit tumor-specific immune responses

Due to their capacity to induce primary immune responses, dendritic cells (DC) are attractive vectors for immunotherapy of cancer. Yet the targeting of tumor Ags to DC remains a challenge. Here we show that immature human monocyte-derived DC capture various killed tumor cells, including Jurkat T cell lymphoma, malignant melanoma, and prostate carcinoma. DC loaded with killed tumor cells induce MHC class I- and class II-restricted proliferation of autologous CD8+ and CD4+ T cells, demonstrating cross-presentation of tumor cell-derived Ags. Furthermore, tumor-loaded DC elicit expansion of CTL with cytotoxic activity against the tumor cells used for immunization. CTL elicited by DC loaded with the PC3 prostate carcinoma cell bodies kill another prostate carcinoma cell line, DU145, suggesting recognition of shared Ags. Finally, CTL elicited by DC loaded with killed LNCap prostate carcinoma cells, which express prostate specific Ag (PSA), are able to kill PSA peptide-pulsed T2 cells. This demonstrates that induced CTL activity is not only due to alloantigens, and that alloantigens do not prevent the activation of T cells specific for tumor-associated Ags. This approach opens the possibility of using allogeneic tumor cells as a source of tumor Ag for antitumor therapies.     

Direct interactions between intestinal immune cells and the diet

Comment on: Li Y, et al. Cell. 2011; 147:629-40.     

Dendritic cells in glomerulonephritis

Renal biopsies (n = 45) from patients with various forms of glomerulonephritis (GN), comprising mesangial IgA-GN (n = 25), focal glomerular sclerosis (n = 13) and acute GN (n = 7), were examined by double staining immunocytochemistry (APAAP, streptavidinperoxidase) using unconjugated monoclonal antibodies (Ab) against (i) the CD1b antigen expressed on dendritic cells (DCs), (ii) the invariant chain (Ii), and (iii) biotin-conjugated Ab against HLA-DR. In normal control kidneys (n = 7) without interstitial inflammation, CD1b-positive DCs were not detected. Glomerular endothelial cells and a few cells in mesangial areas showed double staining with the Ab against HLA-DR in Ii. In GN without active interstitial inflammation (n = 9), CD1b-positive DCs were not found. In biopsies with interstitial inflammation (n = 36) CDlb-positive DCs were found interspersed among other inflammatory cells. In seven of the biopsies showing IgA-GN DCs were seen in the vicinity of those glomeruli that exhibited either crescents or glomerular sclerosis with splitting of Bowman’s capsule. In proximal tubular epithelial cells de novo expression of HLA-DR/Ii-chain was only seen when DCs were present. We conclude that in different forms of GN: (i) CDlb-positive DCs play an important role in the development of interstitial inflammation, and (ii) their presence may be related to the de novo coexpression of HLA-DR/Ii in tubular epithelial cells, possibly mediated through the production of interferon γ and other cytokines. Supported by the Deutsche Forschungsgemeinschaft (Wa 698/2-1)     

Dendritic cell vaccination and immune monitoring

We exploited dendritic cells (DC) to vaccinate melanoma patients. We recently demonstrated a statistical significant correlation between favorable clinical outcome and the presence of vaccine-related tumor antigen-specific T cells in delayed type hypersensitivity (DTH) skin biopsies. However, favorable clinical outcome is only observed in a minority of the treated patients. Therefore, it is obvious that current DC-based protocols need to be improved. For this reason, we study in small proof of principle trials the fate, interactions and effectiveness of the injected DC.     

Dendritic cells and C-type lectin receptors: coupling innate to adaptive immune responses

Dendritic cells (DCs) have an important function in the initiation and differentiation of immune responses, linking innate information to tailored adaptive responses. Depending on the pathogen invading the body, specific immune responses are built up that are crucial for eliminating the pathogen from the host. Host recognition of invading microorganisms relies on evolutionarily ancient, germline-encoded pattern recognition receptors (PRRs) that are highly expressed on the cell surface of DCs, of which the Toll-like receptors (TLRs) are well characterized and recognize bacterial or viral components. Moreover, they bind a variety of self-proteins released from damaged tissues including several heat-shock proteins. The membrane-associated C-type lectin receptors (CLRs) recognize glycan structures expressed by host cells of the immune system or on specific tissues, which upon recognition allow cellular interactions between DCs and other immune or tissue cells. In addition, CLRs can function as PRRs. In contrast to TLRs, CLRs recognize carbohydrate structures present on the pathogens. Modification of glycan structures on pathogens to mimic host glycans can thereby alter CLR interactions that subsequently modifies DC-induced polarization. In this review, we will discuss in detail how specific glycosylation of antigens can dictate both the innate and adaptive interactions that are mediated by CLRs on DCs and how this balances immune activation and inhibition of DC function.     

Dendritic cells pulsed with live and dead Legionella pneumophila elicit distinct immune responses

Legionella pneumophila is the causative pathogen of Legionnaires' disease, which is characterized by severe pneumonia. In regard to the pathophysiology of Legionella infection, the role of inflammatory phagocytes such as macrophages has been well documented, but the involvement of dendritic cells (DCs) has not been clarified. In this study, we have investigated the immune responses that DCs generate in vitro and in vivo after contact with L. pneumophila. Heat- and formalin-killed L. pneumophila, but not live L. pneumophila, induced immature DCs to undergo similar phenotypic maturation, but the secreted proinflammatory cytokines showed different patterns. The mechanisms of the DC maturation by heat- or formalin-killed L. pneumophila depended, at least in part, on Toll-like receptor 4 signaling or on Legionella LPS, respectively. After transfer to naive mice, DCs pulsed with dead Legionella produced serum Ig isotype responses specific for Legionella, leading to protective immunity against an otherwise lethal respiratory challenge with L. pneumophila. The in vivo immune responses required the Ag presentation of DCs, especially that on MHC class II molecules, and the immunity yielded cross-protection between clinical and environmental strains of L. pneumophila. Although the DC maturation was impaired by live Legionella, macrophages were activated by live as well as dead L. pneumophila, as evidenced by the up-regulation of MHC class II. Finally, DCs, but not macrophages, exhibited a proliferative response to live L. pneumophila that was consistent with their cell cycle progression. These findings provide a better understanding of the role of DCs in adaptive immunity to Legionella infection.     

Dendritic cells permit immune invasion of the CNS in an animal model of multiple sclerosis

Immunization with myelin antigens leads to the development of experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis. The disease can also be induced by the transfer of encephalitogenic CD4+ T helper (T(H)) lymphocytes into naive mice. These T cells need to re-encounter their cognate antigen in the context of major histocompatibility complex (MHC) class II-bearing antigen-presenting cells (APCs) in order to recognize their target. The cell type and location of the APC mediating T-cell entry into the central nervous system (CNS) remain unknown. Here, we show that APCs of the lymphoreticular system and of the CNS parenchyma are dispensable for the immune invasion of the CNS. We also describe that a discrete population of vessel-associated dendritic cells (DCs) is present in human brain tissue. In mice, CD11c+ DCs alone are sufficient to present antigen in vivo to primed myelin-reactive T cells in order to mediate CNS inflammation and clinical disease development.     

Posttranslational regulation of sucrase-isomaltase expression in intestinal crypt and villus cells

Expression and synthesis of sucrase-isomaltase (SI) were studied in human jejunum and in the colon tumor cell lines Caco-2 and HT-29. Twelve monoclonal antibodies produced against the adult human intestinal enzyme were shown to recognize specifically SI by immunoprecipitation of 14C-labeled membrane proteins, analysis of enzyme activities in the immunoprecipitates, and immunoblotting. These antibodies produced markedly different patterns of immunofluorescent staining of the intestinal mucosa. Three of them were specific for the absorptive villus cells, while the other nine also stained the luminal membrane of the proliferative crypt cells, with different intensities which paralleled their ability to recognize SI in immunoblots. Sequential immunoprecipitation of SI solubilized from purified brush borders or entire jejunum with four selected antibodies demonstrated the presence of different forms of the enzyme, expressed by either villus or crypt cells. Two immunologically distinct forms of high mannose precursor (hmP1 and hmP2) were also identified in both jejunal mucosa and colon tumor cells. They were present as monomers and their immunological differences were preserved under various ionic and pH conditions. Pulse-chase studies indicated that, in Caco-2 cells, hmP1 is converted into hmP2 within 30 min of chase, and hmP2 is then processed into the complex-glycosylated precursor destined for the brush border membrane. hmP1 was immunologically related to the mature SI present in crypt cells and lacked the epitopes specific for mature SI expressed by villus cells. These results demonstrated that sucrase-isomaltase is synthesized by both crypt and villus cells, but processing of the cotranslationally glycosylated high mannose precursor is dependent on the state of differentiation of the enterocytes. This may represent a general mechanism for the regulation of expression of differentiated cell products at the post-translational level.     

Dendritic cells in Leishmania infection

Dendritic cells (DCs) are key elements of the immune system, which function as sentinel in the periphery and alert T lymphocytes about the type of invading antigen and address their polarisation, in order to mount an efficacious immune response. Leishmania spp. are parasitic protozoa which may cause severe disease in humans and domestic animals. In this work, the main studies concerning the role of DCs in Leishmania infection are reviewed, in both the murine and human models. In particular, the importance of the genetic status of the hosts and of the different Leishmania species in modulating DC-mediated immune response is examined. In addition, different approaches of DC-based vaccination against experimental leishmaniasis, which could have important future applications, are summarised.     

Dendritic cells in glomerulonephritis.

Renal biopsies (n = 45) from patients with various forms of glomerulonephritis (GN), comprising mesangial IgA-GN (n = 25), focal glomerular sclerosis (n = 13) and acute GN (n = 7), were examined by double staining immunocytochemistry (APAAP, streptavidin-peroxidase) using unconjugated monoclonal antibodies (Ab) against--(i) the CD1b antigen expressed on dendritic cells (DCs), (ii) the invariant chain (Ii), and (iii) biotin-conjugated Ab against HLA-DR. In normal control kidneys (n = 7) without interstitial inflammation, CD1b-positive DCs were not detected. Glomerular endothelial cells and a few cells in mesangial areas showed double staining with the Ab against HLA-DR in Ii. In GN without active interstitial inflammation (n = 9), CD1b-positive DCs were not found. In biopsies with interstitial inflammation (n = 36) CD1b-positive DCs were found interspersed among other inflammatory cells. In seven of the biopsies showing IgA-GN DCs were seen in the vicinity of those glomeruli that exhibited either crescents or glomerular sclerosis with splitting of Bowman's capsule. In proximal tubular epithelial cells de novo expression of HLA-DR/Ii-chain was only seen when DCs were present. We conclude that in different forms of GN: (i) CD1b-positive DCs play an important role in the development of interstitial inflammation, and (ii) their presence may be related to the de novo coexpression of HLA-DR/Ii in tubular epithelial cells, possibly mediated through the production of interferon gamma and other cytokines.