Distribution Of Toll-like Receptor Research Articles

Immunomodulatory Response of the Middle Ear Epithelial Cells in Otitis Media.

The middle ear (ME) epithelium transforms because of changed immunomodulation during infection. The epithelial cells of the tympanic cavity represent the first line of defense in the context of otitis media. They can convert from a typical mucosal site into a respiratory epithelium and vice versa. Our goal is to depict the specific immune response of epithelial cells after infection at the molecular level. The investigations were carried out on healthy and inflamed ME tissue, removed during surgical interventions in mouse and human models, and in a human in-vitro cell model in human ME epithelial cell line. We determined the epithelial localization of the protein expression of Toll- and NOD-like immune receptors and their associated signaling molecules using immunohistochemistry. In addition, we examined growth behavior and gene expression due to direct stimulation and inhibition. We found clinically and immunobiologically confirmed transformation of the inflamed ME epithelium depending on their origin, as well as differences in the distribution of Toll-like receptors and nucleotide-binding oligomerization domain-like receptors in the epithelial cell lining. Dysregulated gene and protein expression of the inflammatory and apoptotic genes could be modulated by stimulation and inhibition in the epithelial cells. The local ME mucosal tissue is believed to modulate downstream immune activity after pathogen invasion via intrinsic cellular mechanism. Using translation approaches to target these molecular pathways may offer more reliable clinical resolution of otitis media in the future.

TLR2 and TLR4 molecules and antigen-presenting cell compositions in cecal tonsils of broiler chicks (Gallus gallus domesticus) in the first two weeks of the post-hatch period.

Chickens do not have lymph nodes. Gut-associated lymphoid tissue is the major immunological organization for the digestive system. Cecal tonsils are an important part of this organization. This study is a descriptive and experimental study that was conducted to determine the histological development of the cecal tonsils and the distribution of Toll-like receptor (TLR) 2, TLR4 and antigen-presenting cells during the first 2weeks of the chick's life. The tissue sections were stained using Crossmon's triple technique, Gordon and Sweet's silver impregnation, and streptavidin-biotin-peroxidase complex methods. The classical tonsil framework with fossa and tonsillar units were observed in 4days cecal tissue. The web of reticular fibres forming the stroma of the tissue had the impression that the lymphoid cells filling in time. The development of cecal tonsil was completed histologically on the day 10 and following day 14 samples. Regardless of the antigenic stimulation, TLR2, TLR4 and CD83, major histocompatibility complex (MHC) class II molecules are present in proximal cecal tissue. However, CD83-positive dendritic cells in the germinal centre were first distinguished on day 7. Furthermore, the high antigen presentation capacity of the cecum with an intense MHC class II molecule expression was determined. Histological and immunohistochemical findings in this study revealed that both innate and adaptive cecal defence mechanisms were in the learning period during the first 2weeks. The learning period of innate immunity may require more detailed research. However, the results obtained in this study will be taken into consideration in the vaccination programmes in chicks.

Distribution of TLR4 and MHC class II molecules of the spleen in broiler chicks treated with and without LPS in the first 2 weeks of the post-hatch period

ABSTRACT1. The purpose of this study was to investigate the distribution of Toll-like receptor-4 (TLR4) and major histocompatibility complex (MHC) class II molecules of the spleen in chicks treated with lipopolysaccharide (LPS) during the first 2 weeks of their life.2. A total of 225 Ross-308 commercial broiler chicks were used. Within the 2-week experimental period, chicks were divided into 5 main groups according to the days of decapitation which were 1, 4, 7, 10 and 14 d after hatch. Each main group had 45 chicks. The main groups were further divided into three subgroups (15 chicks each), which included control chicks (no injection), and phosphate-buffered saline (PBS) and LPS-injected chicks. Spleen samples were collected 1-, 3-, 6-, 12- and 24-h after the PBS or LPS administrations. Tissue sections were stained using streptavidin–biotin–peroxidase complex staining method.3. From 1 d of age, TLR4 positivity was found in the spleen in diffuse granular form. The cells showing intense TLR4 positivity were observed in periellipsoidal lymphoid tissue in 4-d-old chicks. The same cells were determined in the germinal centre of the spleen in 7-d-old chicks. LPS stimulation led to an increase in the intensity of TLR4 positivity in 14-d-old chicks.4. From 1 d of age, MHC class II positivity was found in both white pulp and red pulp. This was higher in 14-d-old chicks injected with LPS than in the controls and the chicks injected with PBS.5. The findings indicate that, from 1 d of age in chicks, the spleen has both non-specific defence elements and the molecules having the information to induce adaptive immunity. In addition, at the end of the 2-week experimental period, it was determined that the spleen had the capacity to recognise antigens.

Distribution of Toll-like Receptor 4 (TLR4) alleles in Romanian cattle breeds

Distribution of Toll-like Receptor 4 (TLR4) alleles in Romanian cattle breeds

Human choroidal melanocytes express functional Toll-like receptors (TLRs)

Toll-like receptors (TLRs) are a class of pattern recognition receptors that sense highly conserved pathogen associated antigenic determinants, triggering an innate immune response and subsequently instructing the adaptive immune system so that together, the pathogen can be eliminated. TLRs are widely distributed in human ocular tissues and cell types, and are active players in ocular inflammation. To date, the presence and function of TLRs on human choroidal melanocytes (HCMs), the most abundant choroidal cell type, have not been characterized. The current study investigated the in vitro and in situ expression and functional status of TLRs on HCMs. HCMs were isolated and cultured from post-mortem human donor eyes, and displayed characteristic melanocyte morphology and MART1 expression – a key melanocyte lineage marker up to passage 5 (P5). In vitro experiments used P1 to P4 HCMs from different donor eyes. Initial quantitative real-time PCR (qPCR) analysis revealed that HCMs (n = 3 donors) expressed specific mRNA transcripts for TLR1-10 and MYD88 (a key adaptor protein initiating the TLR signalling pathway). HCMs were stimulated with a set of synthetic TLR specific agonists and the secretion of pro-inflammatory cytokines, MCP-1 and IL-8, at 24 h measured by ELISA (n = 3 donors). The agonists Pam3CSK4 (TLR1/2), Poly I:C (TLR3), LPS (TLR4), Flagellin (TLR5), and FLS-1 (TLR2) induced a significant increase in the production of MCP-1 and IL-8, compared to untreated cells. Application of biotinylated Pam3CSK4 provided in vitro visualization of receptor-agonist interactions for TLR1/2. We confirmed that cultured HCMs (n = 3 donors) expressed TLR1-6 protein using immunocytochemistry and confocal microscopy. The expression and distribution of TLR 1–6 was also studied in human choroid and retinal pigment epithelium (RPE) sections (n = 3 eyes) using immunofluorescence and confocal microscopy. Strong TLR1-6 immunolabelling that co-localized with melanocyte-dense areas (and RPE) was consistently observed; intraluminal and blood vessel-related cells (including endothelial cells) also expressed several TLRs. Taken together these observations show for the first time that HCMs constitutively express a range of functional TLRs, and as such can contribute to choroidal responses during infection and inflammation.

Genetic ancestry effects on the distribution of toll-like receptors (TLRs) gene polymorphisms in a population of the Atlantic Forest, São Paulo, Brazil

The innate immune system governed by toll-like receptors (TLRs) provides the first line of defense against pathogens. Surface-localized TLR1 and TLR6 are known to detect parasite components. TLR encoding genes were shown to display signatures of recent positive selection in Europeans and might be involved in local adaptation at immune-related genes. To verify the influence of Brazilian population admixture on the distribution of polymorphisms in TLRs, we analyzed the genotype frequencies of 24 polymorphisms distributed across five TLR genes in a Southeastern Brazilian population where autochthonous cases of malaria occur in small foci of transmission. The estimation of ancestry showed mainly European ancestry (63%) followed by African ancestry (22%). Mean proportions of European ancestry differed significantly between the genotypes of the TLR1 (I602S) gene and in the TLR6 (P249S) gene. The chance of having the G allele in TLR1 gene increases as European ancestry increases as well as the chance of having the T allele in the TLR6 gene. The 602S allele is related to a ‘‘hypo-responsiveness’’ possibly explaining the high prevalence of asymptomatic malaria cases in areas of Southeastern Brazil. Our results underline the necessity to include informative ancestry markers in genetic association studies in order to avoid biased results.

Expression and distribution of Toll-like receptor 4 in term placentas of women with gestational diabetes mellitus

Objective To evaluate the expression and distribution of Toll-like receptor 4 (TLR4) in term placentas of women with gestational diabetes mellitus (GDM). Methods Placental samples were collected from 36 normal full-term singleton pregnant women (control group) and 33 full-term singleton pregnant women with GDM who had elective cesarean section in Peking University First Hospital between November 2014 and June 2015. Immunohistochemical assay was used to detect the expression and distribution of TLR4 in placental tissues. T test was used to compare the expression of TLR4 in various cell types of placenta by semi-quantitative analysis. Results (1) TLR4 was expressed in the cell membrane, cytoplasm or nuclei of trophoblast, decidual cells, vascular endothelial cells and amniotic epithelial cells of term placentas. (2) Compared with the control group, the expression of TLR4 was significantly enhanced in trophoblast and decidual cells of GDM women (0.38±0.01 vs 0.31±0.01, 0.39±0.01 vs 0.34±0.01, t=5.218 and 4.525, all P 0.05). Conclusions The expression of TLR4 is different in various cell types of GDM term placentas. Key words: Diabetes, gestational; Placenta; Toll-like receptor 4; Trophoblasts

Genetic polymorphism in postoperative sepsis after open heart surgery in infants.

Sepsis is one of the complications following open heart surgery. Toll-like receptor 2 and toll-interacting protein polymorphism influence the immune response after open heart surgery. This study aimed to assess the genetic distribution of toll-like receptor 2 N199N and toll-interacting protein rs5743867 polymorphism in the development of postoperative sepsis. A prospective cohort study was conducted in 108 children <1-year old who underwent open heart surgery with a Basic Aristotle score ≥6. Patients with an accompanying congenital anomaly, human immunodeficiency virus infection, or history of previous open heart surgery were excluded. The patients' nutritional status and genetic polymorphism were assessed prior to surgery. The results of genetic polymorphism were obtained through genotyping. Patients' ages on the day of surgery and cardiopulmonary bypass times were recorded. The diagnosis of sepsis was established according to Surviving Sepsis Campaign criteria. Postoperative sepsis was observed in 21% of patients. There were 92.6% patients with toll-like receptor 2 N199N polymorphism and 52.8% with toll-interacting protein rs5743867 polymorphism. Toll-like receptor 2 N199N polymorphism tends to increase the risk of sepsis (odds ratio = 1.974; 95% confidence interval: 0.23-16.92; p = 0.504), while toll-interacting protein rs5743867 polymorphism tends to decrease the risk of sepsis (odds ratio = 0.496; 95% confidence interval: 0.19-1.27; p = 0.139) in infants <1-year old undergoing complex open heart surgery.

Age-associated modifications of intestinal permeability and innate immunity in human small intestine.

The physical and immunological properties of the human intestinal epithelial barrier in aging are largely unknown. Ileal biopsies from young (7-12years), adult (20-40years) and aging (67-77years) individuals not showing symptoms of gastrointestinal (GI) pathologies were used to assess levels of inflammatory cytokines, barrier integrity and cytokine production in response to microbial challenges. Increased expression of interleukin (IL)-6, but not interferon (IFN)γ, tumour necrosis factor (TNF)-α and IL-1β was observed during aging; further analysis showed that cluster of differentiation (CD)11c(+) dendritic cells (DCs) are one of the major sources of IL-6in the aging gut and expressed higher levels of CD40. Up-regulated production of IL-6 was accompanied by increased expression of claudin-2 leading to reduced transepithelial electric resistance (TEER); TEER could be restored in invitro and ex vivo cultures by neutralizing anti-IL-6 antibody. In contrast, expression of zonula occludens-1 (ZO-1), occludin and junctional-adhesion molecule-A1 did not vary with age and overall permeability to macromolecules was not affected. Finally, cytokine production in response to different microbial stimuli was assessed in a polarized invitro organ culture (IVOC). IL-8 production in response to flagellin declined progressively with age although the expression and distribution of toll-like receptor (TLR)-5 on intestinal epithelial cells (IECs) remained unchanged. Also, flagellin-induced production of IL-6 was less pronounced in aging individuals. In contrast, TNF-α production in response to probiotics (VSL#3) did not decline with age; however, in our experimental model probiotics did not down-regulate the production of IL-6 and expression of claudin-2. These data suggested that aging affects properties of the intestinal barrier likely to impact on age-associated disturbances, both locally and systemically.

Uncomplicated diverticular disease: innate and adaptive immunity in human gut mucosa before and after rifaximin.

Background/Aim. Uncomplicated diverticular disease (UDD) is a frequent condition in adults. The pathogenesis of symptoms remains unknown. Bacteria are able to interact with Toll-like receptors (TLRs) and to induce inflammation through both innate immunity and T-cell recruitment. We investigated the pattern of TLRs 2 and 4 and the intestinal homing in patients with UDD before and after a course of Rifaximin. Methods. Forty consecutive patients with UDD and 20 healthy asymptomatic subjects were enrolled. Among UDD patients, 20 were assigned to a 2-month course of treatment with Rifaximin 1.2 g/day for 15 days/month and 20 received placebo. Blood sample and colonic biopsies were obtained from patients and controls. The samples were collected and analyzed at baseline and at the end of treatment. Flow cytometry was performed using monoclonal antibodies (CD3, CD4, CD8, CD103, TCR-gamma/delta, CD14, TLR2, and TLR4). Results. In UDD, TLR2 and TLR4 expression on immune cell subpopulations from blood and mucosa of the affected colon are altered as compared with controls. Rifaximin treatment induced significant modifications of altered conditions. Conclusions. Our data show the role of TLRs in the development of inflammation in UDD. TLRs distribution is altered in UDD and these alterations are reversed after antibiotic treatment. This trial is registered with ClinicalTrials.gov: NCT02068482.

Original article Toll-like receptors as an innate immunity bridge to neuroinflammation in medulloblastoma

The relationship between inflammation, immunity and cancer is widely accepted but mechanisms mediating this relationship remain unknown. Our present study was undertaken to examine the presence and distribution of Toll-like receptors (TLRs) in necrotic areas of medulloblastoma. These receptors fulfil the criteria postulated for the receptors of innate immunity and signalling from TLRs induces synthesis of various pro-inflammatory cytokines, enzymes and mediators. The study was performed on human medulloblastoma samples containing areas of necrosis within the tumour and/or within the normal nerve tissue at the periphery of the tumour. Proteins of four TLRs: TLR 2, 3, 4 and 9 were detected in the tissue with the immunohistochemical method using the specific antibodies. Two types of necrotic areas were found. In the first type, the area of dead cells was surrounded by undifferentiated medulloblastoma cells. A lot of these cells expressed TLR 2 and TLR 3 antigens. TLR 2 was also expressed on the wall of de novo formed blood vessels that fill tumour regions already cleared from dead cells. The second type of necrotic areas were found at the periphery of the tumour and composed of normal nerve tissue cells. TLR 2, TLR 3 and TLR 9 were detected in hypertrophic glia cells. Our findings show a new function of TLRs as sensors of pathogens released by medulloblastoma dead cells. This new function may provide a key link connecting innate immunity, neuroinflammation and angiogenesis in the tumour.

A comparison between isolated blood dendritic cells and monocyte‐derived dendritic cells in pigs

Various dendritic cell (DC) populations exist that differ in phenotype and ability to present antigen to T cells. For example, plasmacytoid DCs (pDCs) are less potent T cell activators compared with conventional DCs (cDCs). Here, we compared porcine blood DCs (BDCs), containing pDCs and cDCs, and monocyte-derived DCs (MoDC), consisting of cDCs, in their phenotype, ability to uptake antigen, activation and maturation and their ability to present antigen to autologous T cells. Pigs represent an important animal model, whose immune system in many respects closely resembles that of humans. For example, the distribution of Toll-like receptors is similar to that of humans, in contrast to that of mice. Here we demonstrate that both populations endocytose foreign material. Following lipopolysaccharide stimulation, CD80/86 and chemokine receptor (CCR)7 expression was increased in both populations as was the expression of the chemokine ligands (CCL)-2, CCL-4, CCL-20 and CXCL-2. Although basal and post-stimulation protein concentrations of interleukins 6 and 8 and tumour necrosis factor-alpha were higher in MoDCs, protein concentrations showed a higher fold increase in BDCs. Antigen-specific proliferation of autologous T cells was induced by MoDCs and BDCs. Interestingly, while MoDCs induced stronger proliferation in naive T cells, no difference in proliferation was observed when primed T cells were studied. These results demonstrate that isolated porcine BDCs are highly responsive to stimulation with lipopolysaccharide and are functionally able to drive primed T-cell proliferation to the same extent as MoDCs.

Immunohistochemical localization of Toll‐like receptors 1–10 in periodontitis

In periodontitis, bacteria and pathogen-associated molecular patterns are sensed by Toll-like receptors (TLRs), which initiate intracellular signaling cascades that may lead to host inflammation. In this study, the expression and distribution of TLRs (TLR-1 to TLR-10) were immunohistochemically detected in gingival epithelium and connective tissue. Immunohistochemistry was used for the localization of TLRs in gingival tissue samples from 10 patients with chronic periodontitis and 10 healthy controls; these samples were obtained during routine periodontal flap operations and during extraction operations performed for retained wisdom teeth, respectively. For the evaluation, epithelial layers were stratified to basal, spinous, and superficial layers, and the percentages of TLR-positive cells were determined. Both healthy and periodontitis gingival tissues expressed all TLRs except TLR-10. In patients with periodontitis, epithelial cells showed increased TLR expression towards the basal layer. Healthy controls showed more variable cellular TLR expression and distribution between the layers of epithelium. In the connective tissue, consistently higher TLR expression was found within the periodontitis group compared to the healthy group. For the first time, the cellular expression and distribution of TLR-1 to TLR-10 have been studied in periodontitis, indicating that TLR-1 to TLR-9 are differentially expressed both in connective tissue and epithelial layers. Except for TLR-7 and TLR-8, all the other TLRs showed statistically significant differences between patients with periodontitis and healthy controls, suggesting their involvement in the pathogenesis of periodontitis.

An expanding role of Toll-like receptors in sepsis-induced acute kidney injury

AMONG THE VARIOUS CAUSES OF acute kidney injury (AKI) in hospitalized patients, sepsis remains the most elusive and challenging for the practicing nephrologist. Decades of intensive basic, translational, and clinical research have failed to significantly alter the grim outcome of sepsis and sepsisinduced AKI (13). Nevertheless, active bench research continues to fuel the hope for successful therapies that will eventually

Sepsis induces changes in the expression and distribution of Toll-like receptor 4 in the rat kidney

Toll-like receptors (TLRs) are now recognized as the major receptors for microbial pathogens on cells of the innate immune system. Recently, TLRs were also identified in many organs including the kidney. However, the cellular distribution and role of these renal TLRs remain largely unknown. In this paper, we investigated the expression of TLR4 in a cecal ligation and puncture (CLP) model of sepsis in Sprague-Dawley rats utilizing fluorescence microscopy. In sham animals, TLR4 was expressed predominantly in Tamm-Horsfall protein (THP)-positive tubules. In CLP animals, TLR4 expression increased markedly in all tubules (proximal and distal), glomeruli, and the renal vasculature. The staining showed a strong apical distribution in all tubules. A moderately less intense cellular signal colocalized partially with the Golgi apparatus. In addition, kidneys from septic rats showed increased expression of CD14 and THP. They each colocalized strongly with TLR4, albeit in different tubular segments. We also imaged the kidneys of live septic animals with two-photon microscopy after fluorescent lipopolysaccharide (LPS) injection. Within 10 min, LPS was seen at the brush border of some proximal tubules. Within 60 min, LPS was fully cytoplasmic in proximal tubules. Conversely, distal tubules showed no LPS uptake. We conclude that TLR4, CD14, and THP have specific renal cellular and tubular expression patterns that are markedly affected by sepsis. Systemic endotoxin can freely access the tubular and cellular sites where these proteins are present. Therefore, locally expressed TLRs and other interacting proteins could potentially modulate the renal response to systemic sepsis.

Antibodies against human Toll-like receptors (TLRs): TLR distribution and localization in human dendritic cells

We have produced monoclonal antibodies (mAbs) against human Toll-like receptors (TLRs). These mAbs recognize the natural conformation of the extracellular domain leucine-rich repeats and, thereby, are suitable for immunoprecipitation, flow cytometric analysis and immunostaining. Using these mAbs, we determined the distribution of TLRs in a variety of human cell populations. Human TLRs that recognize bacterial components, particularly TLR-1, TLR-2, TLR-4 and TLR-6, reside on the cell surface and are expressed in myeloid and monocyte-derived dendritic cells (DCs) but not in plasmacytoid DCs (pDCs). Human TLR-3 resides in putative endosomes in myeloid DCs. Thus, the human myeloid DC subset harbors a unique and distinctive TLR repertoire. These mAbs will be useful to test the localization and distribution of human TLRs in a variety of cells and organs. Functional studies of human TLRs will also be feasible since certain of them are function-blocking mAbs.

Antibodies against human Toll-like receptors (TLRs): TLR distribution and localization in human dendritic cells

We have produced monoclonal antibodies (mAbs) against human Toll-like receptors (TLRs). These mAbs recognize the natural conformation of the extracellular domain leucine-rich repeats and, thereby, are suitable for immunoprecipitation, flow cytometric analysis and immunostaining. Using these mAbs, we determined the distribution of TLRs in a variety of human cell populations. Human TLRs that recognize bacterial components, particularly TLR-1, TLR-2, TLR-4 and TLR-6, reside on the cell surface and are expressed in myeloid and monocyte-derived dendritic cells (DCs) but not in plasmacytoid DCs (pDCs). Human TLR-3 resides in putative endosomes in myeloid DCs. Thus, the human myeloid DC subset harbors a unique and distinctive TLR repertoire. These mAbs will be useful to test the localization and distribution of human TLRs in a variety of cells and organs. Functional studies of human TLRs will also be feasible since certain of them are function-blocking mAbs.

Characterization of Toll-like receptors in the female reproductive tract in humans

Rapid innate immune defences against infection involve the recognition of invading pathogens by specific pattern recognition receptors recently attributed to the family of Toll-like receptors (TLR). Little is known about the in vivo protein expression or distribution of TLR in the female reproductive tract in humans. It is likely that TLR distribution in the female reproductive tract reflects the immunological tolerance to the commensal organisms in lower parts of the tract (vagina, ectocervix and, partially, endocervix) and the intolerance to commensal microbial flora in the upper tract (the uterus and uterine tubes). Using immunohistochemistry techniques, distribution of TLR1-6 was studied in surgical sections from the vagina, ecto- and endocervix, endometrium and uterine tubes, obtained from patients undergoing abdominal hysterectomy for benign gynaecological conditions. TLR1, 2, 3, 5 and 6 were present in the epithelia of different regions of female reproductive tract. However, TLR4 was only present in the endocervix, endometrium and uterine tubes and absent in vagina and ectocervix. In addition, a secretory form of TLR4 seems to be produced by the endocervical glands. TLR4 may play an important role in modulation of immunological tolerance in the lower parts of the female reproductive tract, and in host defence against ascending infection.

Immunohistochemical distribution of Toll-like receptor 4 in term and preterm human placentas from normal and complicated pregnancy including chorioamnionitis

Recently discovered Toll-like receptors (TLRs) are essential for the induction of innate immune responses. One member of the TLR family, TLR4 mediates lipopolysaccharide (bacterial endotoxin)-induced inflammatory responses. Although the innate immune system appears to be important in the pathogenesis of infection-induced preterm delivery, the distribution of TLRs in human placenta is poorly understood. Here we investigated the expression of TLR4 protein in 43 human placentas obtained from normal and complicated pregnancies delivered in the second and third trimesters, using immunohistochemistry. TLR4 was localized to the extravillous trophoblasts, intermediate trophoblasts/X cells in the degenerative villi, and villous Hofbauer cells of all preterm and term placentas examined and to the inflammatory cells in placentas with chorioamnionitis (CAM). The villous Hofbauer cells of preterm CAM placentas demonstrated increased TLR4 immunoreactivity compared with those of preterm placentas without CAM or those of term placentas with or without CAM. These results suggest an important role of the villous Hofbauer cells in the activation of innate immune system in response to infectious pathogens in preterm placentas. Elucidation of biological functions of placental TLR4 under physiological conditions requires further investigation.

Toll-like receptor expression in murine DC subsets: lack of TLR7 expression by CD8 alpha+ DC correlates with unresponsiveness to imidazoquinolines.

Toll-like receptors (TLR) recognize microbial and viral patterns and activate dendritic cells (DC). TLR distribution among human DC subsets is heterogeneous: plasmacytoid DC (PDC) express TLR1, 7 and 9, while other DC types do not express TLR9 but express other TLR. Here, we report that mRNA for most TLR is expressed at similar levels by murine splenic DC sub-types, including PDC, but that TLR3 is preferentially expressed by CD8 alpha(+) DC while TLR5 and TLR7 are selectively absent from the same subset. Consistent with the latter, TLR7 ligand activates CD8 alpha(-) DC and PDC, but not CD8 alpha(+) DC as measured by survival ex vivo, up-regulation of surface markers and production of IL-12p40. These data suggest that the dichotomy in TLR expression between plasmacytoid and non-plasmacytoid DC is not conserved between species. However, lack of TLR7 expression could restrict the involvement of CD8 alpha(+) DC in recognition of certain mouse pathogens.