Collection of lymph-borne dendritic cells in the rat

Antigen-Presenting B Cells Program the Efferent Lymph T Helper Cell Response

B cells interact with T follicular helper (Tfh) cells in germinal centers (GCs) to generate high-affinity antibodies. Much less is known about how cognate T–B-cell interactions influence Th cells that enter circulation and peripheral tissues. Therefore, we generated mice lacking MHC-II expressing B cells and, by thoracic duct cannulation, analyzed Th cells in the efferent lymph at defined intervals post-immunization. Focusing on gut-draining mesenteric lymph nodes (MLNs), we show that antigen-specific α₄β₇⁺ gut-homing effector Th cells enter the circulation prior to CXCR5⁺PD-1⁺ Tfh-like cells. B cells appear to have no or limited impact on the early generation and egress of gut-homing Th cells but are critical for the subsequent appearance of Tfh-like cells that peak in the lymph before GCs have developed. At this stage, antigen-presenting B cells also reduce the proportion of α₄β₇⁺ Th cells in the MLN and efferent lymph. Furthermore, cognate B-cell interaction drives a broad transcriptional program in Th cells, including IL-4 that is confined to the Tfh cell lineage. The IL-4-producing Tfh-like cells originate from Bcl6⁺ precursors in the LNs and have gut-homing capacity. Hence, B cells program the efferent lymph Th cell response within a limited window of time after antigenic challenge.

Lung dendritic cells migrate to the spleen to prime long-lived TCF1hi memory CD8+ T cell precursors after influenza infection

[Figure: see text].

The Mononuclear Phagocyte System of the Rat

The laboratory rat continues to be the model of choice for many studies of physiology, behavior, and complex human diseases. Cells of the mononuclear phagocyte system (MPS; monocytes, macrophages, and dendritic cells) are abundant residents in every tissue in the body and regulate postnatal development, homeostasis, and innate and acquired immunity. Recruitment and proliferation of MPS cells is an essential component of both initiation and resolution of inflammation. The large majority of current knowledge of MPS biology is derived from studies of inbred mice, but advances in technology and resources have eliminated many of the advantages of the mouse as a model. In this article, we review the tools available and the current state of knowledge of development, homeostasis, regulation, and diversity within the MPS of the rat.

Mucosal CD8 T Cell Responses Are Shaped by Batf3-DC After Foodborne Listeria monocytogenes Infection

While immune responses have been rigorously examined after intravenous Listeria monocytogenes (Lm) infection, less is understood about its dissemination from the intestines or the induction of adaptive immunity after more physiologic models of foodborne infection. Consequently, this study focused on early events in the intestinal mucosa and draining mesenteric lymph nodes (MLN) using foodborne infection of mice with Lm modified to invade murine intestinal epithelium (InlA^MLm). InlA^MLm trafficked intracellularly from the intestines to the MLN and were associated with Batf3-independent dendritic cells (DC) in the lymphatics. Consistent with this, InlA^MLm initially disseminated from the gut to the MLN normally in Batf3^–/– mice. Activated migratory DC accumulated in the MLN by 3 days post-infection and surrounded foci of InlA^MLm. At this time Batf3^–/– mice displayed reduced InlA^MLm burdens, implicating cDC1 in maximal bacterial accumulation in the MLN. Batf3^–/– mice also exhibited profound defects in the induction and gut-homing of InlA^MLm-specific effector CD8 T cells. Restoration of pathogen burden did not rescue antigen-specific CD8 T cell responses in Batf3^–/– mice, indicating a critical role for Batf3 in generating anti-InlA^MLm immunity following foodborne infection. Collectively, these data suggest that DC play diverse, dynamic roles in the early events following foodborne InlA^MLm infection and in driving the establishment of intestinal Lm-specific effector T cells.

Dendritic Cell Subsets in Intestinal Immunity and Inflammation

The mammalian intestine is a complex environment that is constantly exposed to Ags derived from food, microbiota, and metabolites. Intestinal dendritic cells (DC) have the responsibility of establishing oral tolerance against these Ags while initiating immune responses against mucosal pathogens. We now know that DC are a heterogeneous population of innate immune cells composed of classical and monocyte-derived DC, Langerhans cells, and plasmacytoid DC. In the intestine, DC are found in organized lymphoid tissues, such as the mesenteric lymph nodes and Peyer's patches, as well as in the lamina propria. In this Brief Review, we review recent work that describes a division of labor between and collaboration among gut DC subsets in the context of intestinal homeostasis and inflammation. Understanding relationships between DC subtypes and their biological functions will rationalize oral vaccine design and will provide insights into treatments that quiet pathological intestinal inflammation.

Lymphatic Distribution of Etanercept Following Intravenous and Subcutaneous Delivery to Rats

PURPOSE

The purpose of this work was to investigate the role of the lymphatic system in the pharmacokinetics of etanercept, a fusion protein.

METHODS

Etanercept 1 mg/kg was administered intravenously (IV) and subcutaneously (SC) to thoracic lymph duct-cannulated and sham-operated control rats. Blood and lymph samples were obtained for up to 6 days.

RESULTS

Model-based SC bioavailability of etanercept was 65.2% in the control group. In lymph-cannulated rats, etanercept concentration in the lymph was consistently lower than in serum following IV dosing; and the concentration in the lymph was significantly higher than in serum after SC injection. The absorption occurred predominantly through the lymphatic pathway (82.7%), and only 17.3% by direct uptake into the central compartment (blood pathway). Lymphatic cannulation reduced the area under the serum concentration-time curve by 28% in IV group and by 91% in SC group. A mechanistic pharmacokinetic model that combined dual absorption pathways with redistribution of the systemically available protein drug into lymph was developed. The model successfully captured serum and lymph data in all groups simultaneously, and all parameters were estimated with sufficient precision.

CONCLUSIONS

Lymphatic system was shown to play an essential role in systemic disposition and SC absorption of etanercept.

Salmonella enterica Serovar Typhimurium Travels to Mesenteric Lymph Nodes Both with Host Cells and Autonomously

Salmonella infection is a globally important cause of gastroenteritis and systemic disease and is a useful tool to study immune responses in the intestine. Although mechanisms leading to immune responses against Salmonella have been extensively studied, questions remain about how bacteria travel from the intestinal mucosa to the mesenteric lymph nodes (MLN), a key site for Ag presentation. In this study, we used a mouse model of infection with Salmonella enterica serovar Typhimurium (STM) to identify changes in intestinal immune cells induced during early infection. We then used fluorescently labeled STM to identify interactions with immune cells from the site of infection through migration in lymph to the MLN. We show that viable STM can be carried in the lymph by any subset of migrating dendritic cells but not by macrophages. Moreover, approximately half of the STM in lymph are not associated with cells at all and travel autonomously. Within the MLN, STM associates with dendritic cells and B cells but predominantly with MLN-resident macrophages. In conclusion, we describe the routes used by STM to spread systemically in the period immediately postinfection. This deeper understanding of the infection process could open new avenues for controlling it.

Immunostimulatory Agent Evaluation: Lymphoid Tissue Extraction and Injection Route-Dependent Dendritic Cell Activation

For evaluation of a new therapeutic agent for immunotherapy or vaccination, analysis of immune cell activation in lymphatic tissues is essential. Here, we investigated immunological effects of a novel lipid-DNA immunostimulant in nanoparticle form from different administration routes in the mouse: oral, intranasal, subcutaneous, footpad, intraperitoneal, and intravenous. These injections will directly influence the immune response, and harvesting lymphatic tissues and analysis of dendritic cell (DC) activation in the tissues are crucial parts of these evaluations. The extraction of mediastinal lymph nodes (mLNs) is important but quite complex because of the size and location of this organ. A stepwise procedure for harvesting the inguinal lymph node (iLN), mLN, and spleen and analyzing DC activation by flow cytometry is described.

Enhanced incorporation of dietary DHA into lymph phospholipids by altering its molecular carrier

Several previous studies indicated that for optimal uptake by the brain, docosahexaenoic acid (DHA) should be present as phospholipid in the plasma. However most of dietary DHA is absorbed as triacylglycerol (TAG) because it is released as free fatty acid during digestion of either TAG-DHA (fish oil) or sn-2-DHA phospholipid (krill oil), and subsequently incorporated into TAG of chylomicrons. We tested the hypothesis that the absorption of DHA as phospholipid can be increased if it is present in the sn-1 position of dietary phospholipid or in lysophosphatidylcholine (LPC), because it would escape the hydrolysis by pancreatic phospholipase A2. We infused micelle containing the DHA either as LPC or as free acid, into the duodenum of lymph cannulated rats, and analyzed the chylomicrons and HDL of the lymph for the DHA-containing lipids. The results show that while the total amount of DHA absorbed was comparable from the two types of micelle, the percentage of DHA recovered in lymph phospholipids was 5 times greater with LPC-DHA, compared to free DHA. Furthermore, the amount of DHA recovered in lymph HDL was increased by 2-fold when LPC-DHA micelle was infused. These results could potentially lead to a novel strategy to increase brain DHA levels through the diet.

Adoptive Transfer of Dendritic Cells Expressing Fas Ligand Modulates Intestinal Inflammation in a Model of Inflammatory Bowel Disease

Background

Inflammatory bowel diseases (IBD) are chronic relapsing inflammatory conditions of unknown cause and likely result from the loss of immunological tolerance, which leads to over-activation of the gut immune system. Gut macrophages and dendritic cells (DCs) are essential for maintaining tolerance, but can also contribute to the inflammatory response in conditions such as IBD. Current therapies for IBD are limited by high costs and unwanted toxicities and side effects. The possibility of reducing intestinal inflammation with DCs genetically engineered to over-express the apoptosis-inducing FasL (FasL-DCs) has not yet been explored.

Objective

Investigate the immunomodulatory effect of administering FasL-DCs in the rat trinitrobenzene sulfonic acid (TNBS) model of acute colitis.

Methods

Expression of FasL on DCs isolated from the mesenteric lymph nodes (MLNs) of normal and TNBS-colitis rats was determined by flow cytometry. Primary rat bone marrow DCs were transfected with rat FasL plasmid (FasL-DCs) or empty vector (EV-DCs). The effect of these DCs on T cell IFNγ secretion and apoptosis was determined by ELISPOT and flow cytometry for Annexin V, respectively. Rats received FasL-DCs or EV-DCs intraperitoneally 96 and 48 hours prior to colitis induction with TNBS. Colonic T cell and neutrophil infiltration was determined by immunohistochemistry for CD3 and myeloperoxidase activity assay, respectively. Macrophage number and phenotype was measured by double immunofluorescence for CD68 and inducible Nitric Oxide Synthase.

Results

MLN dendritic cells from normal rats expressed more FasL than those from colitic rats. Compared to EV-DCs, FasL-DCs reduced T cell IFNγ secretion and increased T cell apoptosis in vitro. Adoptive transfer of FasL-DCs decreased macroscopic and microscopic damage scores and reduced colonic T cells, neutrophils, and proinflammatory macrophages when compared to EV-DC adoptive transfer.

Conclusion

FasL-DCs are effective at treating colonic inflammation in this model of IBD and represent a possible new treatment for patients with IBD.

Long-Term Catheterization of the Intestinal Lymph Trunk and Collection of Lymph in Neonatal Pigs

Catheterization of the intestinal lymph trunk in neonatal pigs is a technique allowing for the long-term collection of large quantities of intestinal (central) efferent lymph. Importantly, the collection of central lymph from the intestine enables researchers to study both the mechanisms and lipid constitutes associated with lipid metabolism, intestinal inflammation and cancer metastasis, as well as cells involved in immune function and immunosurveillance. A ventral mid-line surgical approach permits excellent surgical exposure to the cranial abdomen and relatively easy access to the intestinal lymph trunk vessel that lies near the pancreas and the right ventral segment of the portal vein underneath the visceral aspect of the right liver lobe. The vessel is meticulously dissected and released from the surrounding fascia and then dilated with sutures allowing for insertion and subsequent securing of the catheter into the vessel. The catheter is exteriorized and approximately 1 L/24 hr of lymph is collected over a 7 day period. While this technique enables the collection of large quantities of central lymph over an extended period of time, the success depends on careful surgical dissection, tissue handling and close attention to proper surgical technique. This is particularly important with surgeries in young animals as the lymph vessels can easily tear, potentially leading to surgical and experimental failure. The video demonstrates an excellent surgical technique for the collection of intestinal lymph.

MyD88 Signaling Regulates Steady-State Migration of Intestinal CD103+ Dendritic Cells Independently of TNF-α and the Gut Microbiota

Intestinal homeostasis and induction of systemic tolerance to fed Ags (i.e., oral tolerance) rely on the steady-state migration of small intestinal lamina propria dendritic cells (DCs) into draining mesenteric lymph nodes (MLN). The majority of these migratory DCs express the α integrin chain CD103, and in this study we demonstrate that the steady-state mobilization of CD103(+) DCs into the MLN is in part governed by the IL-1R family/TLR signaling adaptor molecule MyD88. Similar to mice with complete MyD88 deficiency, specific deletion of MyD88 in DCs resulted in a 50-60% reduction in short-term accumulation of both CD103(+)CD11b(+) and CD103(+)CD11b(-) DCs in the MLN. DC migration was independent of caspase-1, which is responsible for the inflammasome-dependent proteolytic activation of IL-1 cytokine family members, and was not affected by treatment with broad-spectrum antibiotics. Consistent with the latter finding, the proportion and phenotypic composition of DCs were similar in mesenteric lymph from germ-free and conventionally housed mice. Although TNF-α was required for CD103(+) DC migration to the MLN after oral administration of the TLR7 agonist R848, it was not required for the steady-state migration of these cells. Similarly, TLR signaling through the adaptor molecule Toll/IL-1R domain-containing adapter inducing IFN-β and downstream production of type I IFN were not required for steady-state CD103(+) DC migration. Taken together, our results demonstrate that MyD88 signaling in DCs, independently of the microbiota and TNF-α, is required for optimal steady-state migration of small intestinal lamina propria CD103(+) DCs into the MLN.

Neuroenteric axis modulates the balance of regulatory T cells and T-helper 17 cells in the mesenteric lymph node following trauma/hemorrhagic shock

CD103(+) dendritic cells (DCs) continuously migrate from the intestine to the mesenteric lymph nodes (MLNs) and maintain tolerance by driving the development of regulatory T cells (Treg) in the gut. The relative expression of Treg and T-helper 17 (Th17) cells determines the balance between tolerance and immunity in the gut. We hypothesized that trauma/hemorrhagic shock (T/HS) would decrease the CD103(+) DC population in the mesenteric lymph and alter the Treg-to-Th17 ratio in the MLN. We further hypothesized that vagus nerve stimulation (VNS) would promote tolerance to inflammation by increasing the Treg-to-Th17 ratio in the MLN after injury. Male rats were assigned to sham shock (SS), trauma/sham shock (T/SS), or T/HS. T/HS was induced by laparotomy and 60 min of HS (blood pressure 35 mmHg) followed by fluid resuscitation. A separate cohort of animals underwent cervical VNS after the HS phase. MLN samples were collected 24 h after resuscitation. The CD103(+) DC population and Treg-to-Th17 cell ratio in the MLN were decreased after T/HS compared with SS and T/SS, suggesting a shift to an inflammatory response. VNS prevented the T/HS-induced decrease in the CD103(+) DC population and increased the Treg-to-Th17 ratio compared with T/HS alone. VNS alters the gut inflammatory response to injury by modulating the Treg-Th17 cell balance in the MLN. VNS promotes tolerance to inflammation in the gut, further supporting its ability to modulate the inflammatory set point and alter the response to injury.

Vagal nerve stimulation modulates the dendritic cell profile in posthemorrhagic shock mesenteric lymph

BACKGROUND

Previous studies have established that posthemorrhagic shock mesenteric lymph (PHSML) contains proinflammatory mediators, while the cellular basis of PHSML is less well characterized in acute models of injury. CD103 dendritic cells (DCs) have been identified in the mesenteric lymph (ML) in models of chronic intestinal inflammation, suggesting an important role in the gut response to injury. We have previously demonstrated the ability of vagal nerve stimulation (VNS) to prevent gut barrier failure after trauma/hemorrhagic shock (T/HS); however, the ability of VNS to alter ML DCs is unknown. We hypothesized that the CD103 MHC-II DC population would change in PHSML and that VNS would prevent injury-induced changes in this population in PHSML.

METHODS

Male Sprague-Dawley rats were randomly assigned to trauma/sham shock or T/HS. T/HS was induced by midline laparotomy and 60 minutes of HS (blood pressure, 35 mm Hg), followed by fluid resuscitation. A separate cohort of animals underwent cervical VNS after the HS phase. Gut tissue was harvested at 2 hours after injury for histologic analysis. ML was collected during the pre-HS, HS, and post-HS phase. For flow cytometric analysis, ML cells were subjected to staining with CD103 and MHC-II antibodies, and this cell population was compared in the pre-HS and post-HS phase from the same animal. The CD4Foxp3 cell (T reg) population in the ML node (MLN) was also tested to determine effects of CD103 DC modulation in the ML.

RESULTS

VNS reduced histologic gut injury and ML flow seen after injury. The CD103 MHC-II DC population in the PHSML was significantly decreased compared with pre-HS and was associated with decreased T reg expression in the MLN. VNS prevented the injury-induced decrease in the CD103 MHC-II+ DC population in the ML and restored the T reg population in the MLN.

CONCLUSION

These findings suggest that VNS mediates the inflammatory responses in ML DCs and MLN T reg cells by affecting the set point of T/HS responsiveness.

Interleukin-22 binding protein (IL-22BP) is constitutively expressed by a subset of conventional dendritic cells and is strongly induced by retinoic acid

Interleukin-22 (IL-22) is mainly produced at barrier surfaces by T cells and innate lymphoid cells and is crucial to maintain epithelial integrity. However, dysregulated IL-22 action leads to deleterious inflammation and is involved in diseases such as psoriasis, intestinal inflammation, and cancer. IL-22 binding protein (IL-22BP) is a soluble inhibitory IL-22 receptor and may represent a crucial regulator of IL-22. We show both in rats and mice that, in the steady state, the main source of IL-22BP is constituted by a subset of conventional dendritic cells (DCs) in lymphoid and non-lymphoid tissues. In mouse intestine, IL-22BP was specifically expressed in lamina propria CD103(+)CD11b(+) DC. In humans, IL-22BP was expressed in immature monocyte-derived DC and strongly induced by retinoic acid but dramatically reduced upon maturation. Our data suggest that a subset of immature DCs may actively participate in the regulation of IL-22 activity in the gut by producing high levels of IL-22BP.

Intestinal CD103(-) dendritic cells migrate in lymph and prime effector T cells

Intestinal dendritic cells (DCs) continuously migrate through lymphatics to mesenteric lymph nodes where they initiate immunity or tolerance. Recent research has focused on populations of intestinal DCs expressing CD103. Here we demonstrate, for the first time, the presence of two distinct CD103(-) DC subsets in intestinal lymph. Similar to CD103(+) DCs, these intestine-derived CD103(-) DCs are responsive to Flt3 and they efficiently prime and confer a gut-homing phenotype to naive T cells. However, uniquely among intestinal DCs, CD103(-) CD11b(+) CX(3)CR1(int) lymph DCs induce the differentiation of both interferon-γ and interleukin-17-producing effector T cells, even in the absence of overt stimulation. Priming by CD103(-) CD11b(+) DCs represents a novel mechanism for the rapid generation of effector T-cell responses in the gut. Therefore, these cells may prove to be valuable targets for the treatment of intestinal inflammation or in the development of effective oral vaccines.

Expression of HLA-B27 causes loss of migratory dendritic cells in a rat model of spondylarthritis

OBJECTIVE

In rats transgenic for human HLA-B27 and β(2) -microglobulin (B27-transgenic rats), colitis and peripheral inflammation develop spontaneously. Therefore, B27-transgenic rats provide a model of spondylarthritis. Because inflammation in these rats requires CD4+ T lymphocytes and involves intestinal pathology, we hypothesized that dendritic cells (DCs) that migrate from the intestine and control CD4+ T cell differentiation would be aberrant in B27-transgenic rats.

METHODS

Migrating intestinal lymph DCs were collected via thoracic duct cannulation from B27-transgenic and control (HLA-B7-transgenic or nontransgenic) rats. The phenotypes of these DCs and of mesenteric lymph node DCs were assessed by flow cytometry. The ability of DCs to differentiate from bone marrow precursors in vitro was also assessed.

RESULTS

Lymph DCs showed increased activation and, strikingly, lacked the specific DC population that is important for maintaining tolerance to self-antigens. This population of DCs was also depleted from the mesenteric lymph nodes of B27-transgenic rats. Furthermore, in vitro culture of DCs from bone marrow precursors revealed a defect in the ability of B27-transgenic rats to produce DCs of the migratory phenotype, although the DCs that were generated induced enhanced interleukin-17 (IL-17) production from naive CD4+ T cells.

CONCLUSION

We describe 2 different mechanisms by which HLA-B27 may contribute to inflammatory disease: increased apoptotic death of B27-transgenic DCs that normally function to maintain immunologic tolerance and enhanced IL-17 production from CD4+ T cells stimulated by the surviving B27-transgenic DCs.

D6 facilitates cellular migration and fluid flow to lymph nodes by suppressing lymphatic congestion

Lymphatic endothelial cells are important for efficient flow of antigen-bearing fluid and antigen-presenting cells (APCs) from peripheral sites to lymph nodes (LNs). APC movement to LNs is dependent on the constitutive chemokine receptor CCR7, although how conflicting inflammatory and constitutive chemokine cues are integrated at lymphatic surfaces during this process is not understood. Here we reveal a previously unrecognized aspect of the regulation of this process. The D6 chemokine-scavenging receptor, which is expressed on lymphatic endothelial cells (LECs), maintains lymphatic surfaces free of inflammatory CC-chemokines and minimizes interaction of inflammatory leukocytes with these surfaces. D6 does not alter the level of CCR7 ligands on LECs, thus ensuring selective presentation of homeostatic chemokines for interaction with CCR7(+) APCs. Accordingly, in D6-deficient mice, inflammatory CC-chemokine adherence to LECs results in inappropriate perilymphatic accumulation of inflammatory leukocytes at peripheral inflamed sites and draining LNs. This results in lymphatic congestion and impaired movement of APCs, and fluid, from inflamed sites to LNs. We propose that D6, by suppressing inflammatory chemokine binding to lymphatic surfaces, and thereby preventing inappropriate inflammatory leukocyte adherence, is a key regulator of lymphatic function and a novel, and indispensable, contributor to the integration of innate and adaptive immune responses.

Identification and phenotypic characterization of γδ T cells in rat lymph

γδ T cells represent an unconventional subset of T lymphocytes that are abundant in epithelial tissues and serve as an early immune defense against microbes. We have, for the first time, identified γδ T cells in steady-state thoracic duct lymph (TDL) from rats. The lymph contains γδ T cells expressing CD8 but not CD4, CD25, MHC-II or CD103. The percentage of TDL γδ T cells in rats does not change when the mesenteric lymph nodes (MLN) are surgically removed. Our data suggest that a proportion of γδ T cells migrate from the intestine into rat TDL, under steady-state conditions.

Aberrant immune responses in a mouse with behavioral disorders

BTBR T+tf/J (BTBR) mice have recently been reported to have behaviors that resemble those of autistic individuals, in that this strain has impairments in social interactions and a restricted repetitive and stereotyped pattern of behaviors. Since immune responses, including autoimmune responses, are known to affect behavior, and individuals with autism have aberrant immune activities, we evaluated the immune system of BTBR mice, and compared their immunity and degree of neuroinflammation with that of C57BL/6 (B6) mice, a highly social control strain, and with F1 offspring. Mice were assessed at postnatal day (pnd) 21 and after behavioral analysis at pnd70. BTBR mice had significantly higher amounts of serum IgG and IgE, of IgG anti-brain antibodies (Abs), and of IgG and IgE deposited in the brain, elevated expression of cytokines, especially IL-33 IL-18, and IL-1β in the brain, and an increased proportion of MHC class II-expressing microglia compared to B6 mice. The F1 mice had intermediate levels of Abs and cytokines as well as social activity. The high Ab levels of BTBR mice are in agreement with their increased numbers of CD40(hi)/I-A(hi) B cells and IgG-secreting B cells. Upon immunization with KLH, the BTBR mice produced 2-3 times more anti-KLH Abs than B6 mice. In contrast to humoral immunity, BTBR mice are significantly more susceptible to listeriosis than B6 or BALB/c mice. The Th2-like immune profile of the BTBR mice and their constitutive neuroinflammation suggests that an autoimmune profile is implicated in their aberrant behaviors, as has been suggested for some humans with autism.

Analysis of immune cells draining from the abdominal cavity as a novel tool to study intestinal transplant immunobiology

During intestinal transplant (ITx) operation, intestinal lymphatics are not reconstituted. Consequently, trafficking immune cells drain freely into the abdominal cavity. Our aim was to evaluate whether leucocytes migrating from a transplanted intestine could be recovered from the abdominal draining fluid collected by a peritoneal drainage system in the early post-ITx period, and to determine potential applications of the assessment of draining cellular populations. The cell composition of the abdominal draining fluid was analysed during the first 11 post-ITx days. Using flow cytometry, immune cells from blood and draining fluid samples obtained the same day showed an almost complete lymphopenia in peripheral blood, whereas CD3(+) CD4(+) CD8(-) , CD3(+) CD4(-) CD8(+) and human leucocyte antigen D-related (HLA-DR)(+) CD19(+) lymphocytes were the main populations in the draining fluid. Non-complicated recipients evolved from a mixed leucocyte pattern including granulocytes, monocytes and lymphocytes to an exclusively lymphocytic pattern along the first post-ITx week. At days 1-2 post-Itx, analysis by short tandem repeats fingerprinting of CD3(+) CD8(+) sorted T cells from draining fluid indicated that 50% of cells were from graft origin, whereas by day 11 post-ITx this proportion decreased to fewer than 1%. Our results show for the first time that the abdominal drainage fluid contains mainly immune cells trafficking from the implanted intestine, providing the opportunity to sample lymphocytes draining from the grafted organ along the post-ITx period. Therefore, this analysis may provide information useful for understanding ITx immunobiology and eventually could also be of interest for clinical management.

Isolation of rat intestinal lymph DC

Dendritic cells (DCs) migrate constitutively from the intestine via the lymph to the mesenteric lymph nodes. These migrating intestinal lymph DCs (ilDCs) carry antigens acquired in the intestine and play important roles in both the initiation of immune responses and the maintenance of oral tolerance. The ilDC population is made up of at least three functionally different DC subsets. Like many DC populations, ilDCs are exquisitely sensitive to their environment, changing their phenotype and maturing in response to the procedures associated with their extraction from solid tissues. We have developed and refined a method for collecting and purifying these DC subsets from rats, without inducing them to mature. This method involves two separate surgical procedures, separated by at least 6 weeks. Initially, mesenteric lymph nodes are removed. After the animals have fully recovered we cannulate the thoracic duct and collect the ilDCs on ice, minutes after they have left the lymph vessel. The DCs are then enriched using magnetic beads and purified by flow cytometric sorting. We describe this method here, including our recent refinements to limit the use of the restraining "Bollman" cage.

Intestinal CD103+, but not CX3CR1+, antigen sampling cells migrate in lymph and serve classical dendritic cell functions

Chemokine receptor CX3CR1(+) dendritic cells (DCs) have been suggested to sample intestinal antigens by extending transepithelial dendrites into the gut lumen. Other studies identified CD103(+) DCs in the mucosa, which, through their ability to synthesize retinoic acid (RA), appear to be capable of generating typical signatures of intestinal adaptive immune responses. We report that CD103 and CX3CR1 phenotypically and functionally characterize distinct subsets of lamina propria cells. In contrast to CD103(+) DC, CX3CR1(+) cells represent a nonmigratory gut-resident population with slow turnover rates and poor responses to FLT-3L and granulocyte/macrophage colony-stimulating factor. Direct visualization of cells in lymph vessels and flow cytometry of mouse intestinal lymph revealed that CD103(+) DCs, but not CX3CR1-expressing cells, migrate into the gut draining mesenteric lymph nodes (LNs) under steady-state and inflammatory conditions. Moreover, CX3CR1(+) cells displayed poor T cell stimulatory capacity in vitro and in vivo after direct injection of cells into intestinal lymphatics and appeared to be less efficient at generating RA compared with CD103(+) DC. These findings indicate that selectively CD103(+) DCs serve classical DC functions and initiate adaptive immune responses in local LNs, whereas CX3CR1(+) populations might modulate immune responses directly in the mucosa and serve as first line barrier against invading enteropathogens.

Hyporesponsiveness of intestinal dendritic cells to TLR stimulation is limited to TLR4

Dendritic cells (DCs) are crucial to intestinal immune regulation because of their roles in inducing protective immunity against pathogens while maintaining tolerance to commensal bacteria. Nonetheless, relatively little is known about intestinal DC responsiveness to innate immune stimuli via TLRs. We have previously shown that DCs migrating from the rat intestine in lymph (iLDCs) are hyporesponsive to LPS stimulation, thus possibly preventing harmful immune responses being induced to commensal flora. In this study, to understand how iLDC function is regulated by innate immune stimuli, we have characterized the expression and function of TLRs in iLDCs isolated from the thoracic duct lymph of mesenteric lymphadenectomized rats and compared these with DCs grown from bone marrow in the presence of Flt3 ligand. We show that iLDCs express mRNAs for all TLRs, but express significantly less TLR4 mRNA than bone marrow-derived DCs. Functionally, iLDCs could be activated by TLR agonists representing intestinal pathogen-associated molecular patterns, with the important exception of the TLR4 agonist LPS. Furthermore, we show that DCs in the intestinal wall interact directly with noninvasive bacteria (Bacillus subtilis spores), leading to an increase in the output of activated iLDCs into lymph, and that DCs containing spores are activated selectively. These data highlight a functional difference between TLR4 and other TLRs. As iLDCs can respond to TLR stimulation in vitro, there must be other mechanisms that prevent their activation by commensal bacteria under steady-state conditions.

New insights into the roles of dendritic cells in intestinal immunity and tolerance

Dendritic cells (DCs) play a critical key role in the initiation of immune responses to pathogens. Paradoxically, they also prevent potentially damaging immune responses being directed against the multitude of harmless antigens, to which the body is exposed daily. These roles are particularly important in the intestine, where only a single layer of epithelial cells provides a barrier against billions of commensal microorganisms, pathogens, and food antigens, over a huge surface area. In the intestine, therefore, DCs are required to perform their dual roles very efficiently to protect the body from the dual threats of invading pathogens and unwanted inflammatory reactions. In this review, we first describe the biology of DCs and their interactions with other cells types, paying particular attention to intestinal DCs. We, then, examine the ways in which this biology may become misdirected, resulting in inflammatory bowel disease. Finally, we discuss how DCs potentiate immune responses against viral, bacterial, parasitic infections, and their importance in the pathogenesis of prion diseases. We, therefore, provide an overview of the complex cellular interactions that affect intestinal DCs and control the balance between immunity and tolerance.

CD8+ T lymphocytes protective against malaria liver stages are primed in skin-draining lymph nodes

The success of immunization with irradiated sporozoites is unparalleled among the current vaccination approaches against malaria, but its mechanistic underpinnings have yet to be fully elucidated. Using a model mimicking natural infection by Plasmodium yoelii, we delineated early events governing the development of protective CD8(+) T-cell responses to the circumsporozoite protein. We demonstrate that dendritic cells in cutaneous lymph nodes prime the first cohort of CD8(+) T cells after an infectious mosquito bite. Ablation of these lymphoid sites greatly impairs subsequent development of protective immunity. Activated CD8(+) T cells then travel to systemic sites, including the liver, in a sphingosine-1-phosphate (S1P)-dependent fashion. These effector cells, however, no longer require bone marrow-derived antigen-presenting cells for protection; instead, they recognize antigen on parenchymal cells-presumably parasitized hepatocytes. Therefore, we report an unexpected dichotomy in the tissue restriction of host responses during the development and execution of protective immunity to Plasmodium.