Migratory monocytes and granulocytes are major lymphatic carriers ofSalmonellafrom tissue to draining lymph node

Molecular insights into farm animal and zoonotic Salmonella infections

Salmonella enterica is a facultative intracellular pathogen of worldwide importance. Infections may present in a variety of ways, from asymptomatic colonization to inflammatory diarrhoea or typhoid fever depending on serovar- and host-specific factors. Human diarrhoeal infections are frequently acquired via the food chain and farm environment by virtue of the ability of selected non-typhoidal serovars to colonize the intestines of food-producing animals and contaminate the avian reproductive tract and egg. Colonization of reservoir hosts often occurs in the absence of clinical symptoms; however, some S. enterica serovars threaten animal health owing to their ability to cause acute enteritis or translocate from the intestines to other organs causing fever, septicaemia and abortion. Despite the availability of complete genome sequences of isolates representing several serovars, the molecular mechanisms underlying Salmonella colonization, pathogenesis and transmission in reservoir hosts remain ill-defined. Here we review current knowledge of the bacterial factors influencing colonization of food-producing animals by Salmonella and the basis of host range, differential virulence and zoonotic potential.

Bluetongue virus targets conventional dendritic cells in skin lymph

Bluetongue virus (BTV) is the etiological agent of bluetongue, a hemorrhagic disease of ruminants (particularly sheep), which causes important economic losses around the world. BTV is transmitted primarily via the bites of infected midges, which inject the virus into the ruminant's skin during blood feeding. The virus initially replicates in the draining lymph node and then disseminates to secondary organs where it induces edema, hemorrhages, and necrosis. In this study, we show that ovine conventional dendritic cells (cDCs) are the primary targets of BTV that contribute to the primary dissemination of BTV from the skin to draining lymph nodes. Lymph cDCs support BTV RNA and protein synthesis, as well as the production of infectious virus belonging to several different BTV serotypes, regardless of their level of attenuation. Afferent lymph cell subsets, other than cDCs, showed only marginal levels of BTV protein expression. BTV infection provoked a massive recruitment of cDCs to the sheep skin and afferent lymph, providing cellular targets for infection. Although BTV productively infects cDCs, no negative impact on their physiology was detected. Indeed, BTV infection and protein expression in cDCs enhanced their survival rate. Several serotypes of BTV stimulated the surface expression of the CD80 and CD86 costimulatory molecules on cDCs as well as the mRNA synthesis of cytokines involved in inflammation and immunity, i.e., interleukin-12 (IL-12), IL-1beta, and IL-6. BTV-infected cDCs stimulated antigen-specific CD4 and CD8 proliferation as well as gamma interferon production. BTV initially targets cDCs while preserving their functional properties, reflecting the optimal adaptation of the virus to its host cells for its first spread.

Neutrophils and monocytes transport tumor cell antigens from the peritoneal cavity to secondary lymphoid tissues

Antigen-transporting cells take up pathogens, and then migrate from sites of inflammation to secondary lymphoid tissues to induce an immune response. Among antigen-transporting cells, dendritic cells (DCs) are believed to be the most potent and professional antigen-presenting cells that can stimulate naïve T cells. However, the cells that transport antigens, tumor cell antigens in particular, have not been clearly identified. In this study we have analyzed what types of cells transport tumor cell antigens to secondary lymphoid tissues. We show that neutrophils, monocytes and macrophages but not DCs engulf X-irradiated P388 leukemic cells after their injection into the peritoneal cavity, and that neutrophils and monocytes but not macrophages migrate to the parathymic lymph nodes (pLN), the blood, and then the spleen. The monocytes in the pLN comprise Gr-1(-) and Gr-1(+) ones, and some of these cells express CD11c. Overall, this study demonstrates that neutrophils and monocytes transport tumor cell antigens from the peritoneal cavity to secondary lymphoid tissues.

Plasmacytoid dendritic cells migrate in afferent skin lymph

Conventional dendritic cells enter lymph nodes by migrating from peripheral tissues via the lymphatic route, whereas plasmacytoid dendritic cells (pDC), also called IFN-producing cells (IPC), are described to gain nodes from blood via the high endothelial venules. We demonstrate here that IPC/pDC migrate in the afferent lymph of two large mammals. In sheep, injection of type A CpG oligodinucleotide (ODN) induced lymph cells to produce type I IFN. Furthermore, low-density lymph cells collected at steady state produced type I IFN after stimulation with type A CpG ODN and enveloped viruses. Sheep lymph IPC were found within a minor B(neg)CD11c(neg) subset expressing CD45RB. They presented a plasmacytoid morphology, expressed high levels of TLR-7, TLR-9, and IFN regulatory factor 7 mRNA, induced IFN-gamma production in allogeneic CD4(pos) T cells, and differentiated into dendritic cell-like cells under viral stimulation, thus fulfilling criteria of bona fide pDC. In mini-pig, a CD4(pos)SIRP(pos) subset in afferent lymph cells, corresponding to pDC homologs, produced type I IFN after type A CpG-ODN triggering. Thus, pDC can link innate and acquired immunity by migrating from tissue to draining node via lymph, similarly to conventional dendritic cells.

De l’utilité des animaux domestiques pour la recherche en immunologie

Les recherches en immunologie des animaux domestiques fournissent des données complémentaires à celles menées chez la souris, du fait des « opportunités » qu’offrent ces espèces. Certaines d’entre elles font l’objet de cette communication: approche chirurgicale du fonctionnement in vivo des organes lymphoïdes, interventions in utero pour l’étude de l’ontogénèse du système immunitaire, pertinence de l’étude physiopathologique des infections sur espèces cibles.

Mycobacterium bovis BCG-infected neutrophils and dendritic cells cooperate to induce specific T cell responses in humans and mice

Neutrophils are increasingly thought to modulate dendritic cell (DC) functions. We investigated the role of the neutrophil-DC partnership in the response to Mycobacterium bovis BCG-the vaccine used against tuberculosis. We compared neutrophil-DC crosstalk in humans and mice, searching for functional differences. In both species, neutrophils captured fluorescent BCG-enhanced green fluorescent protein (EGFP) and were more phagocytic than DC. Non-apoptotic BCG-infected neutrophils clustered with immature DC, establishing intimate contacts with dendrites, at which fluorescent intact bacilli were observed. Physical interactions between neutrophils and DC were required for DC activation. Human BCG-infected DC produced interleukin (IL)-10, an inhibitory cytokine, whereas DC exposed to BCG-infected neutrophils produced low to undetectable amounts of the cytokine. Mouse BCG-infected neutrophils induced sustained IL-2 production by DC. Human DC exposed to BCG-infected neutrophils stimulated recall T cell reactivity from vaccinated donors. Mouse DC infected with recombinant ovalbumin (OVA)-producing BCG (rBCG(ova)) elicited proliferation of TCR-OVA-transgenic CD4 and CD8 T cells. Moreover, exposing DC to rBCG(ova)-infected neutrophils enhanced OVA presentation. Thus, in mice and humans, neutrophils help DC to cross-present BCG antigens to T cells. Our results suggest that this "ménage à trois" involving neutrophils, DC and T cells plays a major role in the immune response to BCG.

Neutrophils clear bacteria associated with parasitic nematodes augmenting the development of an effective Th2-type response

Infection with the parasitic nematode Nippostrongylus brasiliensis induces a potent Th2 response; however, little is known about early stages of the innate response that may contribute to protective immunity. To examine early events in this response, chemokine expression in the draining lymph node was examined after N. brasiliensis inoculation. Pronounced increases of several chemokines, including CCL2, were observed. Compared with wild-type mice, elevations in a Gr-1bright population in the draining lymph node was significantly decreased in CCL2-/- mice after N. brasiliensis inoculation. Further flow cytometric and immunofluorescent analysis showed that in wild-type mice, Gr-1+ cells transiently entered and exited the draining lymph node shortly after N. brasiliensis inoculation. The Gr-1bright population was comprised of neutrophils expressing TGF-beta and TNF-alpha. Following Gr-1+ cell depletion, N. brasiliensis infection resulted in transient, but significantly increased levels of IFN-gamma, increased serum IgG2a, reduced Th2 cytokines and serum IgE, greatly increased mortality, and delayed worm expulsion. Furthermore, bacteria were readily detected in vital organs. Infection of Gr-1+ cell-depleted mice with N. brasiliensis larvae that were pretreated with antibiotics prevented bacterial dissemination, Th1 inflammatory responses, and decreases in host survival. This study indicates that parasitic nematodes can be an important vector of potentially harmful bacteria, which is typically controlled by CCL2-dependent neutrophils that ensure the optimal development of Th2 immune responses and parasite resistance.

Phase I study of alpha-galactosylceramide-pulsed antigen presenting cells administration to the nasal submucosa in unresectable or recurrent head and neck cancer

BACKGROUND

Human Valpha24 natural killer T (NKT) cells are activated by the specific ligand, alpha-galactosylceramide (alpha-GalCer), in a CD1d-dependent manner. Potent anti-tumor activity of activated NKT cells has been previously demonstrated.

METHODS

We conducted a phase I study with alpha-GalCer-pulsed antigen presenting cells (APCs) administered in the nasal submucosa of patients with head and neck cancer, and evaluated the safety and feasibility of such a treatment. Nine patients with unresectable or recurrent head and neck cancer received two treatments 1 week apart, of 1 x 10(8) of alpha-GalCer-pulsed autologous APCs into the nasal submucosa.

RESULTS

During the clinical study period, no serious adverse events (Common Terminology Criteria for Adverse Events version 3.0 greater than grade 3) were observed. After the first and the second administration of alpha-GalCer-pulsed APCs, an increased number of NKT cells was observed in four patients and enhanced natural killer activity was detected in the peripheral blood of eight patients.

CONCLUSION

The administration of alpha-GalCer-pulsed APCs into the nasal submucosa was found to be safe and induce anti-tumor activity in some patients.

The contribution of dendritic cells to host defenses against Streptococcus pyogenes

BACKGROUND

Infection with Streptococcus pyogenes remains a significant health care problem. The identification of immune components required for host defenses against S. pyogenes constitutes an important area of research.

METHODS

Here, we have investigated the role played by dendritic cells (DCs) during infection with S. pyogenes by use of a murine infection model.

RESULTS

Our results show that S. pyogenes induced the maturation of murine DCs, which involved the up-regulation of CD40, CD80, CD86, and major histocompatibility complex class II molecules and the production of interleukin (IL)-12 and tumor necrosis factor-alpha. After subcutaneous infection of mice, S. pyogenes disseminated systemically via the draining lymph nodes. The contribution of DCs to bacterial dissemination was negligible, because most microorganisms were found free in lymph nodes. The contribution of DCs to host defenses against S. pyogenes was investigated using CD11c-diphtheria toxin (DT) receptor (DTR) transgenic mice, in which CD11c(high) cells (conventional DCs) can be transiently depleted in vivo by treatment with low doses of DT. We show that ablation of DCs led to increased bacterial dissemination into draining lymph nodes and systemic organs. Furthermore, ablation of DCs abolished IL-12 production, which is required for effective control of infection.

CONCLUSIONS

These data demonstrate that DCs contribute to host defenses against S. pyogenes, likely through the production of IL-12.

Phenotypic characterisation of intestinal dendritic cells in sheep

The present study was undertaken to identify dendritic cells (DCs) in the ileum and rectum of lambs and adult sheep. The distribution of these cells in four different intestinal compartments, i.e. lamina propria, lymphoid follicles, domes and interfollicular areas was assessed, and the presence of these cells in lambs and adult sheep was compared. Specimens were examined by using a number of potential DC markers (CD11c, CD205, MHC class II (MHCII), CD1b and CD209) in immunohistochemical and multicolour immunofluorescent procedures. The ovine ileal and rectal mucosa contain many CD11c+/CD205+ cells with a dendritic morphology, and the majority of these cells co-expressed MHCII. These double-positive cells were also labelled with the CD209 antibody in the lamina propria and interfollicular regions. Only very few cells expressed CD1b. In conclusion, a major DC population in ileum and rectum of sheep co-expressed the CD11c, CD205 and MHCII molecules. The CD209 antibody appeared to be a novel marker for a subpopulation of ovine intestinal DCs.

Afferent and efferent interfaces of lymph nodes are distinguished by expression of lymphatic endothelial markers and chemokines

BACKGROUND

Lymph nodes (LNs) are important sites of connection between the sampled peripheral tissues, the many cells of the immune system, and the blood. The organization of the interface between the afferent and efferent lymphatic vasculature and LN parenchyma is incompletely understood, and obtaining a better understanding of these tissue microenvironments will contribute to an improved understanding of overall lymphatic function.

METHODS AND RESULTS

We used histologic approaches to define the distributions of cells expressing lymphatic endothelial cell (LEC) markers in LNs from healthy, simian immunodeficiency virus (SIV) infected, or Mycobacterium tuberculosis infected cynomolgus macaques. Cells at the afferent and efferent interfaces of LNs from all animals showed differential expression of LEC markers, with podoplanin, Prox-1, and VEGFR3 expressed in both microenvironments, but with LYVE-1 expressed only at the efferent interface. The chemokine CCL20 was uniquely expressed at the afferent interface by cells co-expressing podoplanin, and this expression was increased during SIV or M. tuberculosis infection. In contrast, only a small proportion of cells expressing the CCR7 ligand CCL21 co-expressed podoplanin. Treatment of model LECs with the TLR3 ligand poly(I:C) or gamma-irradiated M. tuberculosis increased production of CCL20 without altering CCL21 or LEC marker expression.

CONCLUSIONS

This study provides a comprehensive mapping of the organization of the lymphatic endothelial network entering and exiting LNs in health and in chronic infectious diseases in a nonhuman primate model. The differences we have defined between the afferent and efferent interfaces of LNs could inform the future design of vaccines and immunotherapies.

Salmonella infection of afferent lymph dendritic cells

The interactions of Salmonella enterica subspecies I serotype Abortusovis (S. Abortusovis) with ovine afferent lymph dendritic cells (ALDCs) were investigated for their ability to deliver Maedi visna virus (MVV) GAG p25 antigens to ALDCs purified from afferent lymph. Salmonellae were found to enter ALDC populations by a process of cell invasion, as confirmed by electron and confocal microscopy. This led to phenotypical changes in ALDC populations, as defined by CD1b and CD14 expression. No differences in the clearance kinetics of intracellular aroA-negative Salmonella from CD1b+ CD14lo and CD1b+ CD14(-) ALDC populations were noted over 72 h. ALDCs were also shown to present MVV GAG p25 expressed by aroA-negative S. Abortusovis to CD4+ T lymphocytes. Thus, the poor immune responses that Salmonella vaccines elicited in large animal models compared with mice are neither a result of an inability of Salmonella to infect large animal DCs nor an inability of these DCs to present delivered antigens. However, the low efficiency of infection of ALDC compared with macrophages or monocyte-derived DCs may account for the poor immune responses induced in large animal models.

Systemic translocation of Salmonella enterica serovar Dublin in cattle occurs predominantly via efferent lymphatics in a cell-free niche and requires type III secretion system 1 (T3SS-1) but not T3SS-2

Salmonella enterica is an important diarrheal pathogen, and infections may involve severe systemic sequelae depending on serovar- and host-specific factors. The molecular mechanisms underlying translocation of host-restricted and -specific serovars of S. enterica from the intestines to distal organs are ill defined. By surgical cannulation of lymph and blood vessels draining the distal ileum in cattle, S. enterica serovar Dublin was observed to translocate predominantly via mesenteric lymph nodes to efferent lymphatics in a manner that correlates with systemic virulence, since the fowl typhoid-associated serovar Gallinarum translocated at a significantly lower level. While both S. enterica serovars Dublin and Gallinarum were intracellular while in the intestinal mucosa and associated with major histocompatibility complex class II-positive cells, the bacteria were predominantly extracellular within efferent lymph. Screening of a library of signature-tagged serovar Dublin mutants following oral inoculation of calves defined the role of 36 virulence-associated loci in enteric and systemic phases of infection. The number and proportion of tagged clones reaching the liver and spleen early after oral infection were identical to the values in efferent lymph, implying that this may be a relevant mode of dissemination. Coinfection studies confirmed that lymphatic translocation requires the function of type III secretion system 1 (T3SS-1) but, remarkably, not T3SS-2. This is the first description of the mode and genetics of systemic translocation of serovar Dublin in its natural host.

Isolation and purification of afferent lymph dendritic cells that drain the skin of cattle

Dendritic cells (DCs) are central to the induction of immune responses and are a pivotal control point that determines the outcome of infectious challenge. Cannulation of afferent lymphatic vessels allows the isolation of large numbers of lymph DCs. First, lymph nodes that are draining the skin are surgically removed (takes approximately 1 h). Over a period of 6-8 weeks, afferent lymphatic vessels re-anastomose with the efferent duct, forming larger 'pseudoafferent' lymphatic vessels that can be surgically cannulated. Surgical cannulation takes 2 h to perform; daily maintenance of the catheter requires 30 min. Isolation of lymph cells requires 1 h and an additional 60-180 min to enrich or purify the DCs. The lymph can be harvested for up to 1 month, with relatively constant cell numbers and subset distribution throughout this period. This technique, although technically demanding, facilitates studies of DCs and other cells that traffic in the lymph in both the steady state and following antigenic exposure.

Cervical duct cannulation in sheep for collection of afferent lymph dendritic cells from head tissues

Pseudo-afferent cervical lymph-duct cannulation in a sheep model allows large amounts of lymph cells to be collected under physiological conditions, carrying immune signaling information from the head tissues, including oro-nasal mucosae. Importantly, large quantities of dendritic cells (DCs) of several subtypes are obtained (up to 8 million per overnight collection), as well as many other trafficking leukocytes. The technique includes three steps: removal of all head lymph nodes on one side (2 h), catheterization of cervical lymph ducts after 2 months (2-3 h) and collection/purification of lymph-cell subsets (4 h). The approach is challenging (1 in 3 success rate) but fruitful, and can be used to study DC subsets under immunomodulation, in order to assess lymph-cell subset dynamic changes and antigen transportation from oro-nasal tissues. This protocol is directed to experienced postdoctoral researchers.

Neutrophils and intracellular pathogens: beyond phagocytosis and killing

Neutrophils are not simply scavenging phagocytes that clear extracellular spaces of rapidly proliferating microbes; they are also active in the control of infections by intracellular pathogens. Several mechanisms for nonphagocytic roles of neutrophils in protective immunity have been put forth over the years but further evidence has recently been accumulating at an increasing pace. In this review, I present the evidence that suggests neutrophils are involved in pathogen shuttling into the lymphoid tissues, in antigen presentation, and in early T cell recruitment and initiation of granuloma organization. Also, a clearer view on the antimicrobial molecules that can be acquired by macrophages to enhance their antimicrobial activity is now emerging. Finally, neutrophils can adversely affect immunity against certain parasites by causing immune deviation.

Presence of neutrophil-bearing antigen in lymphoid organs of immune mice

Neutrophils play a crucial early role during the innate response, but little is known about their possible contribution when an adaptive immune response is installed. A robust neutrophilia and a T helper 1 (Th1) immune response are present after immunization with Complete Freund Adjuvant (CFA). We show that when FITC-labeled OVA was injected into the footpad of OVA/CFA immunized mice, the main OVA-FITC+ cells recruited in draining popliteal lymph nodes (LNs) were neutrophils, with most of them arriving at the LN by means of lymphatic vessels. The development of this OVA-FITC+ neutrophil influx requires an immune response against OVA. The OVA-FITC+ neutrophils present in LNs displayed mainly intracellular TNF-α, and their depletion resulted in an increase in the specific IL-5 levels. These data provide new evidence about the role played by neutrophils in vivo in adaptive immunity.