Maturation of Peyer's patch dendritic cells in vitro upon stimulation via cytokines or CD40 triggering

Mechanisms for the Invasion and Dissemination of Salmonella

Salmonella enterica is a gastroenteric Gram-negative bacterium that can infect both humans and animals and causes millions of illnesses per year around the world. Salmonella infections usually occur after the consumption of contaminated food or water. Infections with Salmonella species can cause diseases ranging from enterocolitis to typhoid fever. Salmonella has developed multiple strategies to invade and establish a systemic infection in the host. Different cell types, including epithelial cells, macrophages, dendritic cells, and M cells, are important in the infection process of Salmonella. Dissemination throughout the body and colonization of remote organs are hallmarks of Salmonella infection. There are several routes for the dissemination of Salmonella typhimurium. This review summarizes the current understanding of the infection mechanisms of Salmonella. Additionally, different routes of Salmonella infection will be discussed. In this review, the strategies used by Salmonella enterica to establish persistent infection will be discussed. Understanding both the bacterial and host factors leading to the successful colonization of Salmonella enterica may enable the rational design of effective therapeutic strategies.

Analysis of Dendritic Cell Function Using Clec9A-DTR Transgenic Mice

The Clec9A-diphtheria toxin receptor (DTR) transgenic mouse strain provides a robust animal model to study the function of lymphoid organ-resident CD8(+) dendritic cells (DCs) and nonlymphoid organ-specific CD103(+) DCs in infectioous diseases and inflammation. Here we describe some basic protocols for CD8(+)/CD103(+) DC isolation, for their in vivo depletion, and for their characterization by multi-color flow cytometry analysis. As an example for in vivo functional characterization of this DC subset, we present here the experimental cerebral malaria model. Furthermore, we illustrate advantages and pitfalls of the Clec9A-DTR system.

Cholera toxin adjuvant promotes a balanced Th1/Th2/Th17 response independently of IL-12 and IL-17 by acting on Gsα in CD11b⁺ DCs

Despite an extensive literature on the mechanism of action of cholera toxin (CT), we still lack critical information about how the toxin acts as an adjuvant and, especially, which dendritic cells (DCs) are the target cells. Although a T helper type 2 (Th2)-skewing effect of CT is most commonly reported, effective priming of Th17 cells as well as suppression of Th1 responses are well documented. However, the ability of CT to block interferon regulatory factor 8 (IRF8) function and interleukin (IL)-12 production in DCs, which blocks CD8α DC and Th1 cell development, is inconsistent with priming of Th1 and CD8 T cells in many other reports. This prompted us to investigate the adjuvant effect of CT in wild-type, IL-12p40-/-, Batf3-/-, and IL-17A-/- mice and in mice that selectively lack the Gsα target protein for CT adenosine diphosphate (ADP)-ribosylation in DCs. We found that CT promoted Th1 priming independently of IL-12, and whereas Th2 and also Th17 responses were augmented, the gut IgA responses did not require IL-17A. Adjuvanticity was intact in Batf3-/- mice, lacking CD8α(+) DCs, but completely lost in mice with Gsα-deficient CD11c cells. Thus, our data demonstrate that the adjuvant effect requires Gsα expression in CD11b(+) DCs, and that priming of mucosal IgA and CD4 T cells appears unbiased and is independent of IL-12 and IL-17A.

A role for syntaxin 3 in the secretion of IL-6 from dendritic cells following activation of toll-like receptors

The role of dendritic cells (DCs) in directing the immune response is due in part to their capacity to produce a range of cytokines. Importantly, DCs are a source of cytokines, which can promote T cell survival and T helper cell differentiation. While it has become evident that soluble-N-ethylmaleimide-sensitive-factor accessory-protein receptors (SNAREs) are involved in membrane fusion and ultimately cytokine release, little is known about which members of this family facilitate the secretion of specific cytokines from DCs. We profiled mRNA of 18 SNARE proteins in DCs in response to activation with a panel of three Toll-like receptors (TLR) ligands and show differential expression of SNAREs in response to their stimulus and subsequent secretion patterns. Of interest, STX3 mRNA was up-regulated in response to TLR4 and TLR7 activation but not TLR2 activation. This correlated with secretion of IL-6 and MIP-1α. Abolishment of STX3 from DCs by RNAi resulted in the attenuation of IL-6 levels and to some extent MIP-1α levels. Analysis of subcellular location of STX3 by confocal microscopy showed translocation of STX3 to the cell membrane only in DCs secreting IL-6 or MIP-1α, indicating a role for STX3 in trafficking of these immune mediators. Given the role of IL-6 in Th17 differentiation, these findings suggest the potential of STX3 as therapeutic target in inflammatory disease.

Oral administration of kefiran induces changes in the balance of immune cells in a murine model

The aim of the present study was to evaluate the effect of the oral administration of kefiran on the balance of immune cells in a murine model. Six week old BALB/c mice were treated with kefiran (300 mg/L) for 0, 2 and 7 days. Kefiran treatment increased the number of IgA+ cells in lamina propria after 2 and 7 days. Percentage of B220+/MHCII(high) cells in mesenteric lymph nodes (2 days) and Peyer's patches (7 days) was higher compared to untreated control mice. An increase of macrophages (F4/80+ cells) was observed in lamina propria and peritoneal cavity (2 and 7 days). In contrast, at day 7, macrophage population decreased in Peyer's patches. These results show the ability of kefiran to modify the balance of immune cells in intestinal mucosa. This property could be highly relevant for the comprehension of the probiotic effect attributed to kefir.

Involvement of dendritic cells in the pathogenesis of inflammatory bowel disease

In conclusion, during inflammation, DCs are likely activated by inflammatory signals and induced to migrate to T cell zones of organized lymphoid tissues where the cells induce T cell responses. In addition to their established role in T cell priming and the induction of tolerance, DCs may act to enhance (or possibly suppress) T cell responses at sites of mucosal inflammation. Determining the importance of DCs in this regard, as well as establishing a potential role for DCs in continuous activation of naive or central memory cells in lymph nodes draining inflammatory sites, will elucidate the role of DCs as a potential therapeutic target for chronic inflammatory diseases, like IBD. Resident intestinal macrophages are noninflammatory and do not efficiently present antigens to intestinal T cells, yet are avidly phagocytic and able to kill internalized organisms. During intestinal inflammation, monocytes are recruited from the blood, become inflammatory macrophages in the inflamed tissue, and are major contributors to tissue destruction and perpetuation of inflammation via their production of chemokines and pro-inflammatory cytokines. Macrophages may also contribute directly to DC activation and maturation, which would drive DCs to present antigens from the bacterial flora to T cells locally within tissue or to more efficiently traffic to T cell zones of lymphoid tissue. Thus, DCs and macrophages have evolved functional niches that promote cooperation in the prevention of untoward intestinal inflammation in the steady state and in the eradication of invasive microorganisms during infection. The balance between suppressing inflammation and promoting host defense is altered in humans with IBD allowing a persistent inflammatory response to commensal bacteria. Based on studies from animal models, the pathogenesis of IBD likely involves either the lack of appropriate regulation from T cells, or an over-production of effector T cells. The end result of these potential mechanisms is the abnormal induction and/or survival of effector T cells and the production of factors such as cytokines by inflammatory macrophages and neutrophils that result in tissue destruction. The destructive process likely involves normally tolerizing DCs, which in the microenvironment of the inflamed mucosa activate T cell responses to normal flora in both draining lymphoid tissues and at sites of inflammation, with macrophages and neutrophils contributing the bulk of inflammatory and destructive cytokines.

How to outwit the enemy: dendritic cells face Salmonella

Salmonella enterica serovar Typhi causes typhoid fever, a serious life-threatening systemic infection. In mice, a similar disease is caused by Salmonella enterica serovar Typhimurium. During typhoid fever, soon after attachment to the mucosal surface of the gut, bacteria come into contact with the dendritic cells (DCs). The ability to sample antigens, process and present them to naïve and mature T cells, in the context of major histocompatibility complex molecules, makes DCs indispensable for mounting a specific and efficient immune response to invading pathogens. These bacteria, however, have evolved a number of mechanisms to interfere with or subvert DC functions. This review aims to describe how Salmonella clashes with dendritic cells at different stages of infection as well as the war strategies of these two opposing sides.

Antigen presenting cells in mucosal sites of veterinary species

The ability of antigen presenting cells, in particular dendritic cells, to integrate a variety of environmental signals, together with their ability to respond appropriately by initiating either tolerance or defensive immune responses make them cells of particular relevance and importance in the mucosal environment. They have been demonstrated in a variety of mucosal tissues in veterinary species and have been characterized to varying degrees, showing that fundamental immunological principles apply throughout all species, but also highlighting some species differences. A major advantage of carrying out immunological research in veterinary species is their size: it is possible to cannulate lymphatic ducts and obtain information about cell migration between different tissues. It is also possible to obtain pure populations of relatively rare cell types such as the plasmacytoid dendritic cells or mucosal dendritic cells ex vivo for the study of immune responses to diseases in their natural host and for other thorough functional studies. Two major myeloid antigen presenting cell (APC) (dendritic cells, DC) cell populations have been described in gut draining lymph and other mucosal sites in ruminants and pigs, characterised by the presence or absence of surface molecules, their enzyme profiles, their ability to phagocytose and their different potential as APC. There is evidence that one of these subsets has migrated from the diffuse mucosal tissue, where it is found as a phagocytic as well as stimulatory APC population, which in turn may be derived from blood macrophages. In addition, the presence and role in viral infection of the IFN-alpha producing plasmacytoid DC in mucosal tissue is discussed, based on studies in pigs.

Breakdown of mucosal immunity in the gut and resultant systemic sensitization by oral antigens in a murine model for systemic lupus erythematosus

Secreted IgA plays a pivotal role in the mucosal immunity to maintain the front line of body defense. We found that the level of fecal IgA was dramatically decreased in aged (NZB x NZW)F(1) (BWF(1)) mice developing lupus nephritis, whereas levels in similarly aged New Zealand Black (NZB) and New Zealand White (NZW) mice remained unchanged compared with young mice. The number of cells obtained from Peyer's patches was markedly decreased in aged BWF(1) mice. Aged BWF(1) mice showed increased susceptibility to pathogenic bacterial infection. Furthermore, oral administration of OVA failed to inhibit secondary IgG response induced by systemic immunization, suggesting defective oral tolerance in aged BWF(1) mice. A significant amount of orally administered OVA was incorporated directly into the intestinal lamina propria in aged BWF(1) mice whereas it was mainly localized in subepithelial domes and interfollicular region in Peyer's patches in young mice. T cells obtained from renal and pulmonary lymph nodes of aged BWF(1) mice that had been orally administered with OVA showed an Ag-specific T cell proliferation, whereas those from young BWF(1), aged NZB, and aged NZW mice did not. Interestingly, aerosol exposure to OVA of aged BWF(1) mice, which had been orally administered with the same Ag, provoked an eosinophil infiltration in the lung. These results demonstrate that mucosal immunity in the gut is impaired and oral Ags induce systemic sensitization instead of oral tolerance in the development of murine lupus.

Intratracheal and intranasal immunization with ovalbumin conjugated withBacillus firmus as a carrier in mice

Inactivated Bacillus firmus (BF), G+ nonpathogenic bacterium of the external environment, was coupled to ovalbumin (OVA) and used in immunization experiments as antigen carrier. Balb/c mice were immunized thrice intra-tracheally and intra-nasally with conjugates of OVA and BF. Surprisingly, administration of OVA-BF conjugates inhibited anti-OVA IgG response in both sera and mucosal secretions if compared to an exposure to OVA alone. The suppression of antigen-specific antibody production was accompanied by promotion of TH1 phenotype.

Mucosal immunity and tolerance in the elderly

Age-associated dysregulation of the immune system of the gastrointestinal (GI) tract has been well documented for both secretory (S)-IgA immunity and oral tolerance. Thus, impaired antigen-specific Ab responses in aged animals and the elderly have been reported. Further, it has been shown that gut-associated lymphoreticular tissue (GALT) mediated immune responses are more susceptible to aging than are lymphoid tissues involved in peripheral immunity. Aging also impairs oral tolerance, which may be of central importance for maintaining GI homeostasis. Thus, as early as 6-8-month-old mice failed to establish systemic unresponsiveness to orally introduced antigens. Despite these studies, the precise mechanisms for impaired GI tract immune system responses remain unclear. The evidence of reduced sizes of Peyer's patches through aging suggests that age-associated mucosal dysregulation may be the result of mucosal inductive tissue dysfunction. Indeed, the frequencies of naive CD4+ T cells and dendritic cells (DCs) in Peyer's patches of aged mice were reduced and this led to a lack of essential cytokine synthesis for the induction of either S-IgA immunity or oral tolerance.

Uptake of antigens from the intestine by dendritic cells

The intestinal immune system responds to ingested antigens in a variety of ways, ranging from tolerance to full immunity. How T cells are instructed to make these differential responses is still unclear. Dendritic cells (DCs) sample enteric antigens in the lamina propria and Peyer's patches, and transport them within the patch or to mesenteric nodes where they are presented to lymphocytes. It is probable that DCs also transmit information that influences the outcome of T cell activation, but the nature of this information and the factors in the intestine that regulate DC behavior and properties are far from clear. We have developed a model in the rat that permits analysis of DCs actually in the process of migration from the intestine to mesenteric nodes. In this paper we will review those aspects of our research that relate to antigen uptake and discuss these in the context of other experimental systems.

Intestinal dendritic cell subsets: differential effects of systemic TLR4 stimulation on migratory fate and activation in vivo

Dendritic cells (DC) present peripheral Ags to T cells in lymph nodes, but also influence their differentiation (tolerance/immunity, Th1/Th2). To investigate how peripheral conditions affect DC properties and might subsequently regulate T cell differentiation, we examined the effects of a potent DC-activating, TLR-4-mediated stimulus, LPS, on rat intestinal and hepatic DC in vivo. Steady-state rat intestinal and hepatic lymph DC are alpha(E2) integrin(high) (CD103) and include two subsets, signal regulatory protein alpha (SIRPalpha)(hi/low), probably representing murine CD8alphaalpha(-/+) DC. Steady-state lamina propria DC are immature; surface MHC class II(low), but steady-state lymph DC are semimature, MHC class II(high), but CD80/86(low). Intravenous LPS induced rapid lamina propria DC emigration and increased lymph DC traffic without altering SIRPalpha(high)/SIRPalpha(low) proportions. CD80/86 expression on lymph or mesenteric node DC was not up-regulated after i.v. LPS. In contrast, i.v. LPS stimulated marked CD80/86 up-regulation on splenic DC. CD80/86 expression on intestinal lymph DC, however, was increased after in vitro culture with TNF-alpha or GM-CSF, but not with up to 5 mug/ml LPS. Steady-state SIRPalpha(low) DC localized to T cell areas of mesenteric nodes, spleen, and Peyer's patch, whereas SIRPalpha(high) DC were excluded from these areas. Intravenous LPS stimulated rapid and abundant SIRPalpha(high) DC accumulation in T cell areas of mesenteric nodes and spleen. In striking contrast, i.v. LPS had no effect on DC numbers or distribution in Peyer's patches. Our results suggest that any explanation of switching between tolerance and immunity as well as involving changes in DC activation status must also take into account differential migration of DC subsets.

Improving M cell mediated transport across mucosal barriers: do certain bacteria hold the keys?

Specialized microfold (M) cells of the follicle-associated epithelium (FAE) of the mucosal-associated lymphoid tissue (MALT) in gut and the respiratory system play an important role in the genesis of both mucosal and systemic immune responses by delivering antigenic substrate to the underlying lymphoid tissue where immune responses start. Although it has been shown that dendritic cells (DC) also have the ability to sample antigens directly from the gut lumen, M cells certainly remain the most important antigen-sampling cell to be investigated in order to devise novel methods to improve mucosal delivery of biologically active compounds. Recently, novel information on the interactions between bacteria and FAE have come to light that unveil further the complex cross-talk taking place at mucosal interfaces between bacteria, epithelial cells and the immune system and which are central to the formation and function of M cells. In particular, it has been shown that M cell mediated transport of antigen across the FAE is improved rapidly by exposure to certain bacteria, thus opening the way to identify new means to achieve a more effective mucosal delivery. Here, these novel findings and their potential in mucosal immunity are analysed and discussed, and new approaches to improve antigen delivery to the mucosal immune system are also proposed.

Targeting of secretory IgA to Peyer's patch dendritic and T cells after transport by intestinal M cells

In addition to being instrumental to the protection of mucosal epithelia, secretory IgA (SIgA) adheres to and is transported by intestinal Peyer's patch (PP) M cells. The possible functional reason for this transport is unknown. We have thus examined in mice the outcome of SIgA delivered from the intestinal lumen to the cells present in the underlying organized mucosa-associated lymphoreticular tissue. We show selective association of SIgA with dendritic cells and CD4(+) T and B lymphocytes recovered from PP in vitro. In vivo, exogenously delivered SIgA is able to enter into multiple PP lining the intestine. In PP, SIgA associates with and is internalized by dendritic cells in the subepithelial dome region, whereas the interaction with CD4(+) T cells is limited to surface binding. Interaction between cells and SIgA is mediated by the IgA moiety and occurs for polymeric and monomeric molecular forms. Thus, although immune exclusion represents the main function of SIgA, transport of the Ab by M cells might promote Ag sampling under neutralizing conditions essential to the homeostasis of mucosal surfaces.

A subset of human dendritic cells in the T cell area of mucosa-associated lymphoid tissue with a high potential to produce TNF-alpha

Recently, a new class of human dendritic cell (DC) precursors has been described in the peripheral blood recognized by the mAb M-DC8. These cells represent approximately 1% of PBMC and acquire several characteristics of myeloid DC upon in vitro culture. In this report we show that M-DC8(+) monocytes secrete in response to LPS >10 times the amount of TNF-alpha as M-DC8(-) monocytes, but produce significantly less IL-10. Consistent with a role in inflammatory responses, we found that M-DC8(+) cells localized in the T cell area of inflamed human tonsils and in the subepithelial dome region of Peyer's patches. In patients with active Crohn's disease, abundant M-DC8(+) cells were detectable in inflamed ileal mucosa, which were entirely depleted after systemic steroid treatment. Our results indicate that M-DC8(+) cells are cells of DC phenotype in inflamed mucosa-associated lymphoid tissue that may contribute to the high level of TNF-alpha production in Crohn's disease. We infer that selective elimination of M-DC8(+) cells in inflammatory diseases has therapeutic potential.

Anatomical basis of tolerance and immunity to intestinal antigens

The intestinal immune system has to discriminate between harmful and beneficial antigens. Although strong protective immunity is essential to prevent invasion by pathogens, equivalent responses against dietary proteins or commensal bacteria can lead to chronic disease. These responses are normally prevented by a complex interplay of regulatory mechanisms. This article reviews the unique aspects of the local microenvironment of the intestinal immune system and discuss how these promote the development of regulatory responses that ensure the maintenance of homeostasis in the gut.

Identification of a new mechanism for bacterial uptake at mucosal surfaces, which is mediated by dendritic cells

Dendritic cells are potent activators of the immune response. They reside in tissues which interface the external environment, but we shall see that they do not perform only a passive role by monitoring microorganisms that have entered the body. Rather, DC can actively participate to microbial entry across mucosal surfaces by creeping between epithelial cells and by internalizing bacteria via their dendrites.

Treatment of an immortalized APC cell line with both cytokines and LPS ensures effective T-cell activation in vitro

Antigen-presenting cells (APCs) are crucial for the generation of a functional immune response to pathogens. Furthermore, there is abundant evidence for their importance in primary T-cell activation, B-cell maturation and maintenance of an ongoing immune response. In the present study, we have analysed phenotypic characteristics and functionality of a p53-deficient APC cell line (JawsII) derived from mouse bone marrow culture. We show that unstimulated JawsII cells express low surface levels of major histocompatibility complex (MHC) and costimulatory molecules, both of which can be upregulated upon treatment with cytokines in vitro. Cytokine stimulation also leads to an enhanced T-cell activation capacity but has only little effect on cytokine release by the JawsII cells themselves. On the contrary, stimulation of the JawsII cells with lipopolysaccharide (LPS) leads to the production and secretion of high amounts of interleukin-1 (IL-1), IL-6 and tumour necrosis factor-alpha (TNF-alpha) but no increase in the surface levels of MHC and costimulatory molecules, and has only little effect on the T-cell activation capacity. Our data suggest that the effects observed upon treatment with cytokines or LPSs are complementary, and that both stimuli are needed for mediating a strong and efficient JawsII cell-dependent T-cell activation.

Clustering of colonic lamina propria CD4(+) T cells to subepithelial dendritic cell aggregates precedes the development of colitis in a murine adoptive transfer model

Initial lesions in inflammatory bowel disease induced during the repopulation of immunodeficient RAG1(-/-) mice with immunocompetent CD4(+) T cells have not been previously described. In this transfer colitis model, we followed CD4(+) T cell repopulation in the host by injecting autofluorescent CD4(+) T cells from congenic, enhanced green fluorescent protein (eGFP)-transgenic mice. This allowed the direct, sensitive, and unambiguous histological detection of the repopulation of the intestinal tract, mesenteric lymph nodes, and spleen of the host with donor eGFP(+) CD4(+) T cells. We identified in RAG1(-/-) mice intestinal dendritic cell (DC) aggregates under the basal crypt epithelium at the mucosa/submucosa junction from which F4/80(+) macrophages were excluded. At Days 8 to 11 posttransfer (before colitis was manifest), CD4(+) T cells clustered and proliferated in CD11c(+) DC aggregates. T cell clustering was most pronounced in the cecum where histologically overt colitis became manifest 5 to 10 days later. Junctional DC aggregates were thus prevalent in the triggering phase of the disease. The data suggest that pathogenic T cell responses inducing inflammatory bowel disease are primed or restimulated in situ in junctional CD4(+) T cell/DC aggregates.

In vivo-matured Langerhans cells continue to take up and process native proteins unlike in vitro-matured counterparts

We have been able to identify the cell subset derived from Langerhans cells in the total dendritic cell population of the peripheral lymph node and hence to follow their trafficking under normal physiological conditions as well as upon skin irritation. As expected, the rapid mobilization of Langerhans cells triggered by inflammatory signals into the draining lymph node correlated with an up-regulation of costimulatory molecules and with an enhanced immunostimulatory capacity. Surprisingly, however, these cells, instead of shutting down, maintain the capacity to capture and process protein Ags during the couple of days they stay alive in stark contrast to in vitro-matured dendritic cells.

Dendritic cells express tight junction proteins and penetrate gut epithelial monolayers to sample bacteria

Penetration of the gut mucosa by pathogens expressing invasion genes is believed to occur mainly through specialized epithelial cells, called M cells, that are located in Peyer's patches. However, Salmonella typhimurium that are deficient in invasion genes encoded by Salmonella pathogenicity island 1 (SPI1) are still able to reach the spleen after oral administration. This suggests the existence of an alternative route for bacterial invasion, one that is independent of M cells. We report here a new mechanism for bacterial uptake in the mucosa tissues that is mediated by dendritic cells (DCs). DCs open the tight junctions between epithelial cells, send dendrites outside the epithelium and directly sample bacteria. In addition, because DCs express tight-junction proteins such as occludin, claudin 1 and zonula occludens 1, the integrity of the epithelial barrier is preserved.

Dendritic cell function is perturbed by Yersinia enterocolitica infection in vitro

Infection with Yersinia enterocolitica is the cause of intestinal or extraintestinal diseases. We investigated the role of dendritic cells (DC), the most potent antigen-presenting cell (APC), in the course of infection with Y. enterocolitica in vitro. For these studies, DC were isolated from human peripheral blood and infected with green fluorescent protein (GFP)-labelled Y. enterocolitica. Bacteria were found within DC by FACS analysis and viable bacteria could be cultured from lysed cells. Within 24 h after infection, DC upregulated CD83 and CD86 followed at day 3, indicating maturation of DC. In contrast, for MHC class II, a marked but transient downregulation was observed at day 3 after infection, and downregulation to a lesser extent for CD80 at day 5. To assess the immunostimulatory capacity of DC, viable infected and uninfected DC were incubated with autologous T cells in the presence of phytohemagglutinin A (PHA). T cell proliferation was significantly reduced at days 4-6 after infection but not thereafter, whereas nonpathogenic Escherichia coli was not able to mimick this suppressive effect of Y. enterocolitica. The same suppression could be observed when infected DC were used in a mixed leucocyte reaction with allogeneic T cells. Thus Y. enterocolitica is able to invade DC, does not induce necrosis or apoptosis, but affects maturation of DC. However, MHC class II-molecules are downregulated initially, which coincides with a diminished immunostimulatory capacity of DC infected with Y. enterocolitica. The diminished immunostimulatory capacity of DC following infection with Y. enterocolitica in vitro might impair or delay elimination of bacteria thereby contributing to pathogenesis of bacterial enteritis or extraintestinal manifestations such as reactive arthritis.

Production of functionally deficient dendritic cells from HTLV-I-infected monocytes: implications for the dendritic cell defect in adult T cell leukemia

Adult T cell leukemia (ATL) is induced by an infection with human T lymphotropic virus type I (HTLV-I) and is accompanied by immunodeficiency. Monocyte-derived immature dendritic cells (DCs) donated by 11 ATL patients were suppressed in the ability to take up fluorescein isothiocyanate (FITC)-dextran and were down-regulated in the expression of CD1a and CD86 antigens (Ags). Monocytes from the patients showed impaired expression of CD14 and HLA-DR Ags. These results suggest intrinsic abnormalities of monocytes and a defect of DC maturation in ATL patients. Therefore, we examined the influence of HTLV-I infection of monocytes on their differentiation to DCs. Monocytes obtained from healthy donors were susceptible to HTLV-I infection in vitro. HTLV-I-infected monocytes were down-regulated in the expression of CD14 Ags, and immature DCs obtained from them expressed CD1a poorly and were impaired in the ability to take up FITC-dextran. Mature DCs differentiated from these cells could not stimulate autologous CD4(+) T cell or CD8(+) T cell proliferation, even after being secondarily pulsed with HTLV-I at an immature DC stage. These results suggest that HTLV-I-infected monocytes cannot properly differentiate to DCs and that this might be one of the important mechanisms producing dysfunctional DCs in ATL patients.

The role of chemokine receptors in primary, effector, and memory immune responses

The immune system is composed of single cells, and its function is entirely dependent on the capacity of these cells to traffic, localize within tissues, and interact with each other in a precisely coordinated fashion. There is growing evidence that the large families of chemokines and chemokine receptors provide a flexible code for regulating cell traffic and positioning in both homeostatic and inflammatory conditions. The regulation of chemokine receptor expression during development and following cell activation explains the complex migratory pathways taken by dendritic cells, T and B lymphocytes, providing new insights into the mechanisms that control priming, effector function, and memory responses.

Improved FACS analysis confirms generation of immature dendritic cells in long-term stromal-dependent spleen cultures

Cells produced in spleen stroma-dependent long-term cultures (LTC) have now been clearly defined as dendritic cells (DC). Characterization of cells by antibody staining and FACS analysis has only been possible using a procedure to quench the high autofluorescence of DC produced in LTC (LTC-DC). The population of large cells produced by the established LTC-X1 culture are homogeneously positive for a number of cell-surface markers expressed by DC. These include CD11c, CD11b, Dec-205, Fc receptor and CD86. They also express markers detectable with the F4/80 and 33D1 antibodies. Cells produced in LTC do not uniformly express the MHC II marker, consistent with an immature DC phenotype. Most cells are weakly positive for MHC II with a small subset of highly positive cells. The quenching method involves staining cells with crystal violet dye, which is taken up within the cell. The importance of optimizimg fluorescent antibody staining assays for delineating DC subsets is indicated and the LTC system is established as a valuable and continuous source of DC precursors.

Identical T cell clones are located within the mouse gut epithelium and lamina propia and circulate in the thoracic duct lymph

Murine gut intraepithelial (IEL) T cell receptor (TCR)-alpha/beta lymphocytes bearing CD8alpha/13 or CD8alpha/alpha coreceptors have been shown previously to express different oligoclonal TCR beta chain repertoires in the same mouse, in agreement with other evidence indicating that these two populations belong to different ontogenic lineages, with only CD8alpha/beta+ IELs being fully thymus dependent. CD8alpha/beta+, but not CD8alpha/alpha+, T lymphocytes are also present in the lamina propria. Here, we show that CD8alpha/beta+ lymphocytes from the lamina propria and the epithelium are both oligoclonal, and that they share the same TCR-beta clonotypes in the same mouse, as is also the case for CD4alpha T cells. Furthermore, identical T cell clones were detected among CD8alpha/beta IELs and CD8alpha/beta+ blasts circulating into the thoracic duct (TD) lymph of the same mouse, whereas TD small lymphocytes are polyclonal. These findings must be considered in light of previous observations showing that T blasts, but not small T lymphocytes, circulating in the TD lymph have the capacity of homing into the gut epithelium and lamina propria. These combined observations have interesting implications for our understanding of the recirculation of gut thymus-dependent lymphocytes and their precursors, and of the events leading up to the selection of their restricted TCR repertoire.

Three chemokines with potential functions in T lymphocyte-independent and -dependent B lymphocyte stimulation

Three clustered mouse chemokine genes, ABCD-1, -2 and -3, are all expressed highly in dendritic cells and, at various levels, in activated B cells. T cell-independently activated B cells express ABCD-1 and -2, but not -3. T cell-dependently activated B cells express all three. ABCD-1 attracts activated CD8+ cytotoxic T cells and CD4+ helper T cells of type 1 and 2. ABCD-2 preferentially attracts type 2 helper T cells, while ABCD-3 does not attract T cells at all. Both ABCD-1 and ABCD-2 bind to the same receptor (CCR4). In addition, ABCD-1 binds to a second, unknown, receptor on a separate T cell population. The three chemokines might guide T cell-independent as well as -dependent responses with two types of CD4+ T cells.

Dissemination of SIV after rectal infection preferentially involves paracolic germinal centers

Homosexual transmission remains a major mode of contamination in developed countries. Early virological and immunological events in lymphoid tissues are known to be important for the outcome of HIV infections. Little data are available, however, on viral dissemination during primary rectal infection. We therefore studied this aspect of rectal infection in rhesus macaques inoculated with the biological isolate SIVmac251. We show that infection is established initially in lymph nodes draining the rectum. Infected cells and virions are localized mainly in germinal centers at that stage. With increasing viral burden, infected cells are found throughout the lymph node parenchyma. In addition the difference in viral load between lymph nodes draining the rectum and other lymph nodes is attenuated or abolished. We discuss this pattern of viral dissemination with respect to the physiology of the mucosal immune system. The pattern and kinetics of viral dissemination after rectal infection have important implications for the development of efficient mucosal vaccines.

Freshly isolated Peyer's patch, but not spleen, dendritic cells produce interleukin 10 and induce the differentiation of T helper type 2 cells

Orally administered antigens often generate immune responses that are distinct from those injected systemically. The role of antigen-presenting cells in determining the type of T helper cell response induced at mucosal versus systemic sites is unclear. Here we examine the phenotypic and functional differences between dendritic cells (DCs) freshly isolated from Peyer's patches (PP) and spleen (SP). Surface phenotypic analysis of CD11c(+) DC populations revealed that PP DCs expressed higher levels of major histocompatibility complex class II molecules, but similar levels of costimulatory molecules and adhesion molecules compared with SP DCs. Freshly isolated, flow cytometrically sorted 98-100% pure CD11c(+) DC populations from PP and SP were compared for their ability to stimulate naive T cells. First, PP DCs were found to be much more potent in stimulating allogeneic T cell proliferation compared with SP DCs. Second, by using naive T cells from ovalbumin peptide-specific T cell receptor transgenic mice, these ex vivo DCs derived from PP, but not from SP, were found to prime for the production of interleukin (IL)-4 and IL-10 (Th2 cytokines). In addition, PP DCs were found to prime T cells for the production of much lower levels of interferon (IFN)-gamma (Th1) compared with SP DCs. The presence of neutralizing antibody against IL-10 in the priming culture dramatically enhanced IFN-gamma production by T cells stimulated with PP DCs. Furthermore, stimulation of freshly isolated PP DCs via the CD40 molecule resulted in secretion of high levels of IL-10, whereas the same stimulus induced no IL-10 secretion from SP DCs. These results suggest that DCs residing in different tissues are capable of inducing distinct immune responses and that this may be related to the distinct cytokines produced by the DCs from these tissues.

Mucosal immunity and inflammation. I. Mucosal dendritic cells: their specialized role in initiating T cell responses

Dendritic cells (DCs) are the most competent antigen-presenting cells known for the induction of primary T cell responses. Functional studies of tissue-resident DCs have been impaired by the rarity of these cells in any given organ. Recent development of isolation procedures allowing extraction of highly purified fresh DC populations has made it possible to study mucosal DCs in distinct mucosa-associated lymphoid tissues. Here, we discuss several recent studies by us and others that describe the tissue-specific phenotype and function of mucosal DCs and speculate on the mechanism by which the resident DCs regulate tissue-specific T cell responses.

Increased antibody production against gut-colonizing Escherichia coli in the presence of the anaerobic bacterium Peptostreptococcus

Germ-free rats were colonized with E. coli alone, or with E. coli plus Lactobacillus acidophilus and a strain of the obligate anaerobic gram-positive species, Peptostreptococcus. The presence of Peptostreptococcus reduced translocation of E. coli, but increased the serum antibody response to E. coli antigen. Whereas the immunoglobulin G (IgG) anti-E. coli antibodies largely represented cross-reactive antibodies, those of the immunoglobulin M (IgM) isotype represented true anti-E. coli antibodies because they could not be absorbed by L. acidophilus or Peptostreptococcus but could with E. coli. We suggest that peptostreptococci prime the gut immune system to other bacterial antigens and that this could be a mechanism behind the reduced translocation of facultative anaerobes in the presence of obligate anaerobes.

Activated murine B lymphocytes and dendritic cells produce a novel CC chemokine which acts selectively on activated T cells

Genes were isolated using the suppression subtractive hybridization method by stimulation of pro/pre B cells with anti-CD40 and interleukin (IL)-4 to mature S mu-Sepsilon-switched cells. One of the strongly upregulated genes encodes a novel murine CC chemokine we have named ABCD-1. The ABCD-1 gene has three exons separated by 1. 2- and 2.7-kb introns. It gives rise to a 2.2-kb transcript containing an open reading frame of 276 nucleotides. Two polyadenylation sites are used, giving rise to cDNAs with either 1550 or 1850 bp of 3' untranslated regions. The open reading frame encodes a 24 amino acid-long leader peptide and a 68 amino acid-long mature protein with a predicted molecular mass of 7.8 kD. ABCD-1 mRNA is found in highest quantities in activated splenic B lymphocytes and dendritic cells. Little chemokine mRNA is present in lung, in unstimulated splenic cells, in thymocytes, and in lymph node cells. No ABCD-1 mRNA is detected in bone marrow, liver, kidney, or brain, in peritoneal exudate cells as well as in the majority of all unstimulated B lineage cells tested. It is also undetectable in Concanavalin A-activated/IL-2-restimulated splenic T cells, and in bone marrow-derived IL-2-induced natural killer cells and IL-3-activated macrophages. Recombinant ABCD-1 revealed a concentration-dependent and specific migration of activated splenic T lymphoblasts in chemotaxis assays. FACS(R) analyses of migrated cells showed no preferential difference in migration of CD4(+) versus CD8(+) T cell blasts. Murine as well as human T cells responded to ABCD-1. Freshly isolated cells from bone marrow, thymus, spleen, and lymph node, IL-2-activated NK cells, and LPS-stimulated splenic cells, all did not show any chemotactic response. Thus, ABCD-1 is the first chemokine produced in large amounts by activated B cells and acting selectively on activated T lymphocytes. Therefore, ABCD-1 is expected to play an important role in the collaboration of dendritic cells and B lymphocytes with T cells in immune responses.