Monocyte Toll-like Receptor Research Articles

P022 Therapeutic effect of adipose tissue-derived stem cell in Interleukin-10 knockout mice

Background: Inflammatory Bowel Disease (IBD) is characterized by chronic intestinal inflammation with unknown etiology. Interleukin-10 Knockout (IL-10 KO) Mice are known to develop intestinal inflammation that resemble CD. We investigated if a human adipose-derived stem cells (h-ASCs) are capable to attenuated colon inflammation in IL-10 KO mice. Methods: h-ASCs were isolated from adipose tissues obtained from human donors. Colitis was induced in the mice by administration of piroxicam orally. Mice treated with intraperitoneal h-ASCs injection (5×105 cells) or normal saline as control after induction of colitis. All mice were euthanized 14 days after colitis. Histopathologic score and level of inflammation related cytokines were evaluated. Comparisons were made between h-ASCs treated or control non-treated IL-10 KO mice and wild type littermate. Results: The flow cytometry showed higher expression of CD105, CD73, CD90, CD44, however, hematopoietic stem cell markers such as CD45, CD34 and CD31 were not expressed in ADSC. Clinical score was lower in h-ASCs treated IL-10 KO mice than in control. Histopathologic assesment of large intestine showed lower inflammatory cells infiltration and less mucosal damage in h-ASCs treated mice than in control. Tissue score was lower in h-ASCs treated IL-10 KO mice than in control. The level of Monocyte chemoattractant protein-1 and Toll-like receptor 4 expression in the large intestine was lower and anti human IL-10 and anti mouse IL-4 in the serum was higher in h-ASCs treated mice. Conclusions: These findings suggested that administration of h-ASCs show beneficial effect on T-cell induced spontaneous colitis model and emerge a therapeutic option in inflammatory bowel disease.

TLR4 expression on monocyte subsets in myocardial infarction

Monocyte toll-like receptor 4 (TLR4) has been implicated in the pathogenesis of atherosclerosis with increased levels in myocardial infarction. The aim of this study was to assess the numbers of TLR4(+) monocytes in each monocyte subset in MI, the expression of TLR4 and association with markers of monocyte activation, inflammation, myocardial damage and postmyocardial infarction (MI) cardiac contractility. Surface expression of TLR4 and numbers of TLR4-expressing monocytes were quantified by flow cytometry of venous blood in 50 patients with ST-elevation MI (STEMI), 48 with non-STEMI (NSTEMI) and 40 with stable coronary artery disease (CAD). These parameters were measured on days 1, 3, 7 and 30 post-MI in STEMI patients. Three monocyte subsets were defined as CD14(++) CD16(-) CCR2(+) (Mon1), CD14(++) CD16(+) CCR2(+) (Mon2) and CD14(+) CD16(++) CCR2(-) (Mon3). Plasma inflammatory cytokines were assessed using cytometric bead arrays. There was a significant increase in counts of TLR4(+) Mon1 and Mon2 in STEMI patients and TLR4(+) Mon2 in NSTEMI patients compared with controls with CAD. Monocyte TLR4(+) expression was similar between the groups, and was not changed during follow-up in STEMI patients. Plasma interleukin-6 (IL6) levels correlated positively with TLR4(+) Mon2 count (r=0.54, P<0.001), but negatively with TLR4 expression on Mon2 (r=-0.33, P=0.021). Following treatment of acute MI, TLR4 expression by individual monocyte subsets is unchanged. An increase in TLR4(+) Mon1 and Mon2 count in patients with STEMI and TLR(+) Mon2 count in those with NSTEMI is due to an increase in monocyte subset count and not to changes in TLR4 expression. Monocyte counts but not TLR4 expression correlate positively with plasma IL6 levels. We suggest that TLR4 expression may not be a reliable marker of monocyte activation in MI.

One week of multifactorial high-stress military ranger training affects Gram-negative signalling

Background. Toll-like receptor 4 (TLR4), especially expressed on monocytes/macrophages, connects microbial and sterile innate immune activation. Lipopolysaccharide (LPS) from Gram-negative bacteria and several endogenous molecules, among others saturated fatty acids (SFAs), are able to induce signalling through this receptor. Downstream inflammatory cytokines orchestrate the immune response. Our aim was to investigate how long-lasting multifactorial stress affects Gram-negative signalling and search for possible correlations between cytokine production and TLR4 expression or SFA concentration. Methods. Eight healthy males were studied during a 7-day ranger-training course with semi-continuous physical strain, together with energy and sleep restrictions. Blood drawn on days 0, 3, 5 and 7 was incubated ex vivo for 6 h with or without LPS 10 ng/mL, whereupon surface expression of TLR4 on CD14+ monocytes and supernatant concentrations of inflammatory cytokines (TNF-α, IL-1β and IL-6) were measured. In addition, plasma free fatty acids were quantified. Results. Monocyte TLR4 expression was elevated throughout the course (p < 0.05 vs. baseline). Corresponding results were found for SFAs. The concentration of TNF-α increased significantly on day 3 and thereafter normalized, and a similar pattern was seen for IL-1β. No correlations were found between cytokine concentrations and monocyte TLR4 expression or plasma SFAs. Conclusion. Multifactorial stress significantly affected ex vivo production of TNF-α and monocyte surface expression of TLR4. In addition, mobilization of fat resulted in increased plasma concentrations of SFAs. No associations between inflammatory cytokines and monocyte TLR4 expression or SFAs were found.

Toll-like receptor 4 gene polymorphism influences dendritic cell in vitro function and clinical outcomes in vaccinated melanoma patients.

Toll-like receptor 4 (TLR4) is expressed on dendritic cells (DCs), sensing environmental danger molecules that induce their activation and maturation. Recently, we reported a method for the production of therapeutic DCs against melanoma, called tumor antigen-presenting cells (TAPCells), using a heat-shocked allogeneic melanoma cell lysate (TRIMEL) as an activation factor and antigen provider. Since TRIMEL contains endogenous TLR4 ligands, we evaluated the role of TLR4 in TAPCells differentiation by antibody neutralization and the association of a Tlr4 polymorphism (896A/G) (Asp299Gly), determined by PCR-RFLP, with the in vitro activation capacity and the clinical outcome of TAPCells-vaccinated patients. Antibody blocking of monocyte TLR4 inhibited surface expression, determined by flow cytometry, of the major histocompatibility complex class I, CCR7, CD80, CD83 and CD86 on TAPCells, reduced interleukin (IL)-6 and tumor necrosis factor -α gene expression evaluated by qRT-PCR, and also inhibited the TAPCells-mediated interferon-γ (IFN-γ) secretion of melanoma-specific CD8(+) T cells determined by ELISpot (p < 0.01). Moreover, CD8(+) T-cell activation capacity was significantly reduced in TAPCells bearing the TLR4 Asp299Gly receptor (p < 0.05). Finally, TAPCells-vaccinated stage-IV melanoma patients bearing the Tlr4 896G allele showed a shortened post-therapy median survival rate compared with those carrying the Tlr4 896A allele (p < 0.05; log-rank test). Our results indicate that TLR4 is a key receptor for the tumor lysate-mediated in vitro generation of clinically efficient antigen-presenting cells. Further analysis of patients included in different vaccine protocols is necessary for definitively establishing a role for TLR4 polymorphism in clinical responses.

The impact of hyaluronan on monocyte Toll-like receptor expression in term infant cord blood

To explore the possible effects of hyaluronan, an endogenous mediator of inflammation, on monocyte surface expression of Toll-like receptors 2 and 4 in human umbilical cord blood ex vivo, and in a model mimicking Gram-negative neonatal sepsis. Term infant cord blood was obtained after elective caesarean sections, n = 15. Both unstimulated and lipopolysaccharide-stimulated (10 ng/mL) blood was incubated with 500 μg/mL high- or low-molecular-weight hyaluronan for 6 h. Expression of Toll-like receptors 2 and 4 on monocytes was measured using flow cytometry, and plasma concentrations of proinflammatory cytokines and matrix metalloproteinase 9 were analysed. RESULTS (MEAN ± SEM): We found a significant decrease in Toll-like receptor 4 expression in the presence of high-molecular-weight hyaluronan (HMW HA) in unstimulated blood (median fluorescence intensity 141 ± 7.3 vs. 163 ± 9.8, p = 0.019). There were no significant changes in Toll-like receptor 2 expression. Levels of cytokines and matrix metalloproteinase 9 increased in the presence of both forms of hyaluronan. Our results confirm that hyaluronan affects the neonatal immune response. The biological significance of these findings requires further clarification. More studies are needed to validate the possible down-modulation of Toll-like receptor 4 exerted by HMW HA.

Analysis of monocyte subsets and toll-like receptor 4 expression in peripheral blood monocytes of women in preterm labor

Preterm labor is associated with both localized inflammation of the uterus and elevated proinflammatory cytokines. Recently, specific roles have been suggested for distinct monocyte subsets and toll-like receptor 4 (TLR4) expression in inflammation. The aim of this study was to determine whether specific monocyte subsets and increased TLR4 expression in monocyte subsets contribute to preterm labor. The study included 30 preterm labor, 40 full-term labor and 20 pregnant women (not in labor). Four-color flow cytometry was used to examine the distribution of three monocyte subsets (CD14+CD16−, CD14highCD16+, and CD14lowCD16+) and the TLR4 expression in each monocyte subset in each group of women. A larger percentage of CD14highCD16+ cells was found in the preterm labor group than in the other groups (P=0.08, P=0.06). Women in preterm labor also showed significantly higher TLR4 expression in all monocyte subsets and increased fluorescence intensity in the CD14+CD16− and CD14highCD16+ cells. Expression of TLR4 and mean fluorescence intensity on each monocyte subset were also significantly correlated. We conclude that women with preterm labor have higher CD16 monocytes, with high concomitant expression of CD14 and enhanced TLR4 expression in monocytes, and that monocyte TLR4 levels could be used as a marker to predict preterm delivery.

Homology modeling and docking studies to explore the novel drug for monocyte differentiation antigen CD14

AbstractMonocyte differentiation antigen CD14 belongs to the leucine rich family. Elevated levels of monocyte differentiation antigen CD14 and toll-like receptor 4 (TLR4) play a major role in inflammatory response and cause ischemic heart diseases, neuropathic pain and LPS (endotoxin) induced septic shock. IAXO compounds (IAXO-101, IAXO-102 and IAXO-103) inhibit the CD14-dependent and TLR4-independent signaling pathways but they have severe side effects. Due to unavailability of human monocyte differentiation antigen CD14 crystal structure, 3D structure was constructed based on template structure (1WWL) using Modeler 9v9. The modeled structure was refined, energy minimized and validated. Binding site residues of human monocyte differentiation antigen CD14 were predicted using CASTp. The existing compounds were explored in ligand.info database via analog search. Docking analysis was carried out by Schrodinger Maestro 9.2. In the present study, six leads with good pharmacological properties were proposed. Lead 1 (-10.8169 Kcal/mol docking score) has good binding affinity with binding site residues of monocyte differentiation antigen CD14 such as Trp-45, Phe-38, Ala-61, Leu-66, Phe-69, Ile-59, Val-73, Val-96, Ala-99, Ala-100, Val-101, Leu-105, Leu-106, and Leu-126. The lead 1 inhibits CD14-dependent and TLR4-independent signaling pathways which in turn control the inflammatory diseases.

Expression profile of Toll-like receptors in monocytes of peripheral blood from osteoarthritic patients undergoing arthroplasty

To investigate the difference in the expression of TLRs in monocytes from patients with/without implants. Blood samples from 21 osteoarthritic patients undergoing joint replacement (11 cases) or arthroscopy (10 cases) were tested. Blood samples were obtained within 24 h before surgery and the third postoperative day to measure cell-associated TLRs by FCM. The results showed that in the absence of clinical infection, implantation of joint prosthesis seems to be associated with a significant decrease in circulating TLR2- and TLR7-positive cells, whereas the decrease in TLR4- and TLR9-positive cells was not statistically significant. A small intervention in the form of knee arthroscopy was without effect. TLRs seem to be affected by the implantation of joint prosthesis, perhaps by migration to and entrapment in peri-implant tissues. Due to their role in innate and adaptive immunity, TLRs may have consequences for the postoperative inflammation and infection.

Association of Blood Monocyte and Platelet Markers with Carotid Artery Characteristics: The Atherosclerosis Risk in Communities Carotid MRI Study

Background: Atherosclerosis is characterized by infiltration of inflammatory cells from circulating blood. Blood cell activation could play an important role in plaque formation. Methods: We analyzed the relationship between blood cellular markers and quantitative measures of carotid wall components in 1,546 participants from the ARIC (Atherosclerosis Risk in Communities) Carotid MRI Study. Carotid imaging was performed using a gadolinium contrast-enhanced MRI and cellular phenotyping by flow cytometry. Results: Monocyte Toll-like receptor (TLR)-2 is associated with larger plaques, while CD14, myeloperoxidase, and TLR-4 associate with smaller. Platelet CD40L is associated with smaller plaques and thinner caps, while P-selectin is associated with smaller core size. Conclusions: Blood cell activation is significantly associated with atherosclerotic changes of the carotid wall.

Low Vitamin D Levels Correlate With the Proinflammatory State in Type 1 Diabetic Subjects With and Without Microvascular Complications

Epidemiologic studies link vitamin D deficiency to onset of type 1 diabetes mellitus (T1DM). T1DM exhibits increased inflammation, which is pronounced with microvascular complications (T1DM-MV). However, there are a paucity of data on vitamin D in T1DM-MV in relation to biomarkers of inflammation, and this formed the aim of the study. Healthy control subjects (n = 36), patients with T1DM (n = 24), and patients with T1DM-MV (n =26) were recruited. Serum vitamin D levels, monocyte toll-like receptor (TLR) 2 and TLR4 expression and nuclear factor-κB (NFκB) activity were assessed. Patients with T1DM and T1DM-MV were significantly vitamin D deficient compared with control subjects (P < .01). There was a significant negative correlation between vitamin D levels and high-sensitivity C-reactive protein, NFκB activity, and TLR4 expression (P < .05). Preincubation with vitamin D significantly decreased lipopolysaccharide-activated TLR4 expression and cytokine levels in monocytes (P < .05). Low vitamin D levels may contribute to increased inflammation in T1DM. Future studies will elucidate the immunomodulatory effects of vitamin D in decreasing vascular risk in this population.

Effects of dexmedetomidine on expression of Toll-like receptor 4 mRNA in rat peripheral blood monocytes exposed to lipopolysaccharide

Objective To investigate the effects of different concentrations of dexmedetomidine on the expression of Toll-like receptor 4 (TLR4) mRNA in rat peripheral blood monocytes exposed to lipopolysaccharide ( LPS ). Methods Peripheral blood monocytes isolated from male Wistar rats were seeded in 24-well plate in RPMI 1640 liquid culture medium in CO2 incubator at 37 ℃ and 5% CO2 for 2 h, and were randomly divided into 5 groups ( n = 8 each): group A negative control; group B was exposed to LPS 1 μg/ml and C, D and E groups were exposed to LPS 1 μg/ml + dexmetomidine 0.5, 5.0 and 50.0 ng/ml respectively. The monocytes were then incubated for 24 h. The concentrations of TNF-α, IL-1β and IL-6 in the supernatant of the cultured monocytes were detected by ELISA. The expression of TLR4 mRNA in the monocytes was detected by RT-PCR.Results Exposure to LPS significantly increased the expression of TLR4 mRNA and the concentrations of TNF-α, IL-1β and IL -6 in group B as compared with group A ( P ＜ 0.01 ). Dexmedetomidine attenuated the LPS-induced increase in the expression of TLR 4 mRNA and the concentrations of TNF-α, IL-1β and IL-6 in a dose-dependent manner ( P ＜0.05or 0.01 ). Conclusion Dexmedetomidine can inhibit the synthesis of TLR4 and inhibit the secretion and dilivery of TNF-α, IL-1β and IL-6 by down-regulating the gene expression of TLR4 in rat peripheral blood monocytes exposed to LPS. Key words: Dexmedetomidine; Lipopolysaccharides; Toll-like receptor 4; Monocytes

Effect of transforming growth factor-β1 on monocyte Toll-like receptor 4 expression in septic rats.

Sepsis is a tough problem in critical ill patients. This study aimed to investigate the dynamic changes of monocyte Toll-like receptor (TLR) 4 expression in peripheral blood of septic rats and to determine the effects of transforming growth factor (TGF)-β1 on TLR4 expression. Altogether 132 clean level SD rats were randomly divided into a control group (n=12), a sepsis model group (n=60), and a TGF-β1 intervention group (n=60). In the sepsis model group and TGF-β1 intervention group, the rats were subdivided into five groups (2-hour group, 6-hour group, 12-hour group, 24-hour group, and 48-hour group), with 12 rats in each group. Cecal ligation puncture (CLP) was performed in the sepsis model group and TGF-β1 intervention group to establish models of sepsis. The rats in the sepsis model group were injected with 1 mL normal saline at the caudal vein 0.5 hour after the model establishment; the rats in the TGF-β1 intervention group were injected with 20 ng/mL or 250 g TGF-β1 0.5 hour after the model establishment. Flow cytometry was used to detect the change of monocyte TLR4 in peripheral blood, and enzyme-linked immunosorbent assay (ELISA) was used to detect the change of TNF-α level in peripheral blood. At 6-12 hours after CLP, the monocyte TLR4 in peripheral blood started to decrease, and reached the lowest level at 12 hours. Compared to the control group, the monocyte TLR4 expression at 6 and 12 hours was lowered significantly (P<0.05). Compared to the sepsis model group at 2, 24 and 48 hours after CLP, the monocyte TLR4 expression in the TGF-β1 intervention group decreased dramatically (P<0.05), but there were no differences between the two groups at 6 and 12 hours respectively. Compared to the control group, the concentration of NF-κ in liver tissue increased significantly 6 hours after CLP (P<0.05). After use of TGF-β1, the concentration of NF-κ was decreased significantly but still higher than that of the control group. Compared to the control group, the concentration of TNF-α in peripheral blood was increased significantly at 2-48 hours after CLP (P<0.05). After use of TGF-β1, TNF-α was further increased. During sepsis, TGF-β1 can decrease the monocyte TLR4 expression and NF-κ in liver tissue, but facilitate the formation of proinflammatory mediator TNF-α. This finding indicates that TGF-β1 may play a role in promoting inflammatory response during sepsis, but this regulation is not via direct regulation of monocyte TLR4 in peripheral blood.

The influence of prolonged cycling on monocyte Toll-like receptor 2 and 4 expression in healthy men

The influence of prolonged cycling on monocyte Toll-like receptor 2 and 4 expression in healthy men

Acute allograft rejection in human liver transplant recipients is associated with signaling through toll‐like receptor 4

Toll-like receptor (TLR) signaling is a crucial step in initiating adaptive immune responses. In addition to recognizing endotoxin, TLR4 also recognizes endogenous ligands ('damage-associated structures'), which are released into the circulation in the peri-transplantation period. TLR2 to a lesser extent also recognizes these endogenous ligands. Multiple studies involving solid organ transplants demonstrate a clear association between TLR4 and allograft rejection. In the present study we assessed whether an association exists between TLR4 and TLR2-dependent responses and acute liver allograft rejection. The sample included 26 liver transplant recipients. Blood was taken pre-transplant and at multiple points over the first 14 days post-transplant. Monocytes were stimulated with TLR4 and TLR2 ligands, lipopolysaccharide and Pam-3-Cys, respectively. Monocyte TLR expression was determined using flow cytometry; enzyme-linked immunosorbent assays measured tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) production. Nine (34.6%) patients experienced rejection. No differences existed in age, sex, disease or immunosuppression between rejectors and non-rejectors. Baseline TLR4 expression was significantly higher in rejectors (1.36 vs 1.02, P=0.01). There was no difference in TLR2 expression. In rejectors, baseline TLR4- and TLR2-dependent production of TNF-α and IL-6 was also significantly increased. Post-transplant, the two groups differed with regard to TLR4-dependent TNF-α production, with rejectors demonstrating progressive downregulation over the first week. Prior to liver transplantation, patients who subsequently experience rejection demonstrate robust TLR4-dependent immune responses, which are not seen in those who do not reject. This supports the theory that damage-associated structures signaling through TLR4 may be responsible for the early activation of alloimmune T-cells, favoring allograft rejection.

Defining a longitudinal survival model to examine forced treadmill running as a countermeasure for diet-induced weight gain

Diet-induced weight gain increases disease risk via disruption of the innate immune system. Flow cytometry is commonly used to assess the immune system; however, in mice such measurements traditionally require terminal procedures and tissue collection to generate sufficient sample. The present study refined an existing flow cytometry method to reduce the number of mice needed to longitudinally measure monocytes. CD-1 male mice were randomly assigned to one of the three groups: DS (diet-induced weight gain + sedentary), DE (diet-induced weight gain + forced treadmill running [total distance 35,755 ± 1832 m]) or NS (normal weight gain + sedentary). DS and DE consumed a 60% fat diet and NS consumed a 10% fat diet ad libitum. Saphenous vein blood samples were collected weekly for a period of six weeks and three-colour flow cytometry was used to measure changes in monocyte (CD11b(+)/14(+)) concentration and cell-surface toll-like receptor 4 (TLR4) expression. DS (18%) and DE (17%) gained more weight than NS (P < 0.001). On a group basis, DS expressed 17% more TLR4 than DE and NS (P = 0.005). The present study demonstrates that a longitudinal survival model can be used to reduce the number of animals needed to complete flow cytometry experiments. Exercise during diet-induced weight prevented some (decreased monocyte TLR4 expression) but not all aspects of innate immune system function.

E0109 The effects of C-reactive protein on Toll-like receptor 4 signal transduction on CD14+ monocyte

ObjectiveTo observe the effects of C-reactive protein (CRP) on Toll-like receptor 4 (TLR4) expression in CD14+ monocyte in human, and the role of CRP in the inflammatory mechanism.MethodsCD14+ monocytes were...

E0110 The effects of atorvastatin on C-reactive protein induced Toll-like receptor 4 expression on CD14+ monocyte

ObjectiveTo observe the effects of atorvastatin on C-reactive protein (CRP) induced Toll-like receptor 4 expression on CD14+ monocyte in human, and anti-inflammatory effect of atorvastatin.MethodsCD14+ monocytes were isolated from blood...

Monocyte and macrophage heterogeneity and Toll-like receptors in the lung

Mononuclear phagocytes are crucial components of the innate host defense system. Cells such as macrophages and monocytes phagocytose and process pathogens, produce inflammatory mediators, and link the innate and the adaptive immune systems. The role of innate immune receptors such as Toll-like receptors (TLRs) in the recognition of pathogens is critical for mounting a precise and targeted immune response. This review focuses attention on the development of monocytes and macrophages, various populations of macrophages, and the expression and function of TLRs on macrophages.

Adding exercise to rosuvastatin treatment: influence on C-reactive protein, monocyte toll-like receptor 4 expression, and inflammatory monocyte (CD14+CD16+) population

Statin treatment and exercise training can reduce markers of inflammation when administered separately. The purpose of this study was to determine the effect of rosuvastatin treatment and the addition of exercise training on circulating markers of inflammation including C-reactive protein (CRP), monocyte toll-like receptor 4 (TLR4) expression, and CD14+CD16+ monocyte population size. Thirty-three hypercholesterolemic and physically inactive subjects were randomly assigned to rosuvastatin (R) or rosuvastatin/exercise (RE) groups. A third group of physically active hypercholesterolemic subjects served as a control (AC). The R and RE groups received rosuvastatin treatment (10 mg/d) for 20 weeks. From week 10 to week 20, the RE group also participated in an exercise training program (3d/wk). Measurements were made at baseline (Pre), week 10 (Mid), and week 20 (Post), and included TLR4 expression on CD14+ monocytes and CD14+CD16+ monocyte population size as determined by 3-color flow cytometry. Serum CRP was quantified by enzyme-linked immunosorbent assay. TLR4 expression on CD14+ monocytes was higher in the R group at week 20. When treatment groups (R and RE) were combined, serum CRP was lower across time. Furthermore, serum CRP and inflammatory monocyte population size were lower in the RE group compared with the R group at the Post time point. When all groups (R, RE, and AC) were combined, TLR4 expression was greater on inflammatory monocytes (CD14+CD16+) compared with classic monocytes (CD14+CD16−) at all time points. In conclusion, rosuvastatin may influence monocyte inflammatory response by increasing TLR4 expression on circulating monocytes. The addition of exercise training to rosuvastatin treatment further lowered CRP and reduced the size of the inflammatory monocyte population, suggesting an additive anti-inflammatory effect of exercise.

The influence of prolonged cycling on monocyte Toll-like receptor 2 and 4 expression in healthy men

Several studies have reported that some immune cell functions including monocyte Toll-like receptor (TLR) expression and antigen presentation are temporarily impaired following acute bouts of strenuous exercise, which could represent an 'open window' to upper respiratory tract infection (URTI). However, we do not know the time course of effects of acute exercise on human monocyte TLR expression. The purpose of the present study was to examine the effects of 1.5 h cycling at 75% VO(2peak) on human monocyte TLR2 and TLR4 expression and how long it takes for TLR expression to return to pre-exercise values. Nine healthy endurance trained males (age 25 +/- 5 years) had blood samples taken before and for up to 24 h after exercise and analysed using flow cytometry. Although there was an increase in the total monocyte cell count at 0, 1 and 4 h post-exercise (P < 0.01), exercise reduced monocyte TLR4 expression (geometric mean fluorescence intensity, corrected for non-specific binding; P < 0.05) by 32 and 45% at 0 and 1 h post-exercise, respectively, compared with pre-exercise values but had returned to baseline values by 4 h post-exercise. There were no statistically significant changes in TLR2 expression after exercise. In addition, a control resting study was conducted on six healthy endurance trained men (age 25 +/- 2 years) to analyse any diurnal changes on monocyte TLR2 and TLR4 expression but no changes were found across time (P > 0.05). This study showed that prolonged cycling at 75% VO(2peak) temporarily reduces TLR4 expression, which may in part be responsible for post-exercise immunodepression.