Impaired Surface Expression of HLA-DR, TLR2, TLR4, and TLR9 in Ex Vivo-In Vitro Stimulated Monocytes from Severely Injured Trauma Patients

Elevation of White Blood Cell Subtypes in Adult Trauma Patients with Stress-Induced Hyperglycemia

BACKGROUND

Blood immune cell subset alterations following trauma can indicate a patient's immune-inflammatory status. This research explored the influence of stress-induced hyperglycemia (SIH) on platelet counts and white blood cell (WBC) subtypes, including the derived indices of the monocyte-to-lymphocyte ratio (MLR), neutrophil-to-lymphocyte ratio (NLR), and platelet-to-lymphocyte ratio (PLR), in trauma patients.

METHODS

We studied 15,480 adult trauma patients admitted from 1 January 1998 to 31 December 2022. They were categorized into four groups: nondiabetic normoglycemia (NDN, n = 11,602), diabetic normoglycemia (DN, n = 1750), SIH (n = 716), and diabetic hyperglycemia (DH, n = 1412). A propensity score-matched cohort was formed after adjusting for age, sex, and comorbidities, allowing for comparing the WBC subtypes and platelet counts.

RESULTS

Patients with SIH exhibited significantly increased counts of monocytes, neutrophils, and lymphocytes in contrast to NDN patients. However, no significant rise in platelet counts was noted in the SIH group. There were no observed increases in these cell counts in either the DN or DH groups.

CONCLUSIONS

Our results demonstrated that trauma patients with SIH showed significantly higher counts of monocytes, neutrophils, and lymphocytes when compared to NDN patients, whereas the DN and DH groups remained unaffected. This underscores the profound association between SIH and elevated levels of specific WBC subtypes.

Biological Phenotyping in Sepsis and Acute Respiratory Distress Syndrome

Heterogeneity in sepsis and acute respiratory distress syndrome (ARDS) is increasingly being recognized as one of the principal barriers to finding efficacious targeted therapies. The advent of multiple high-throughput biological data ("omics"), coupled with the widespread access to increased computational power, has led to the emergence of phenotyping in critical care. Phenotyping aims to use a multitude of data to identify homogenous subgroups within an otherwise heterogenous population. Increasingly, phenotyping schemas are being applied to sepsis and ARDS to increase understanding of these clinical conditions and identify potential therapies. Here we present a selective review of the biological phenotyping schemas applied to sepsis and ARDS. Further, we outline some of the challenges involved in translating these conceptual findings to bedside clinical decision-making tools.

Immune hyporeactivity to bacteria and multiple TLR-ligands, yet no response to checkpoint inhibition in patients just after meeting Sepsis-3 criteria

Rationale

The immune profile of sepsis patients is incompletely understood and hyperinflammation and hypoinflammation may occur concurrently or sequentially. Immune checkpoint inhibition (ICI) may counter hypoinflammation but effects are uncertain. We tested the reactivity of septic whole blood to bacteria, Toll-like receptor (TLR) ligands and to ICI.

Methods

Whole blood assays of 61 patients’ samples within 24h of meeting sepsis-3 criteria and 12 age and sex-matched healthy volunteers. Measurements included pattern/danger-associated molecular pattern (P/DAMP), cytokine concentrations at baseline and in response to TLR 2, 4, and 7/8 ligands, heat-inactivated Staphylococcus aureus or Escherichia coli, E.coli lipopolysaccharide (LPS), concentration of soluble and cellular immune checkpoint molecules, and cytokine concentrations in response to ICI directed against programmed-death receptor 1 (PD1), PD1-ligand 1, or cytotoxic T-lymphocyte antigen 4, both in the absence and presence of LPS.

Main results

In sepsis, concentrations of P/DAMPs and inflammatory cytokines were increased and the latter increased further upon incubation ex vivo. However, cytokine responses to TLR 2, 4, and 7/8 ligands, heat-inactivated S. aureus or E. coli, and E. coli LPS were all depressed. Depression of the response to LPS was associated with increased in-hospital mortality. Despite increased PD-1 expression on monocytes and T-cells, and monocyte CTLA-4 expression, however, addition of corresponding checkpoint inhibitors to assays failed to increase inflammatory cytokine concentrations in the absence and presence of LPS.

Conclusion

Patients first meeting Sepsis-3 criteria reveal 1) depressed responses to multiple TLR-ligands, bacteria, and bacterial LPS, despite concomitant inflammation, but 2) no response to immune checkpoint inhibition.

Protective Effects of Engineered Lactobacillus crispatus on Intrauterine Adhesions in Mice via Delivering CXCL12

Endometrial injury is the main cause of intrauterine adhesions (IUA), and there is currently no effective prevention and treatment. Immune cells play an important role in damage repair by sensing the change in the microenvironment. Exogenous CXCL12 can promote tissue regeneration and repair by recruiting immune cells, but its effect and possible mechanism on endometrial regeneration and repair have not been reported. In the present study, we constructed an engineered a Lactobacillus crispatus strain by transforming a pMG36e plasmid carrying a CXCL12 gene into the bacterium, and developed two animal models, the intrauterine adhesion mice with or without diabetes to evaluate the positive effects of this strain on the prevention of IUA after accepting intrauterine surgery in normal and diabetic mice. The results showed that vaginal application of L. crispatus-pMG36e-mCXCL12 strains significantly diminished the levels of pro-inflammatory factors interleukin-1β (IL-1β) and tumour necrosis factor-α (TNF-α) in serum and uterine tissues of IUA mice, and resulted in the inhibition of the inflammatory (toll-like receptor 4/nuclear factor-κb, TLR4/NF-κB) and fibrotic (transforming growth factor-β1/smads, TGF-β1/Smads) signalling pathways in the uterine tissues. The high-throughput sequencing results further indicated that treatment with L. crispatus-pMG36e-mCXCL12 strains greatly increased the abundance of Lactobacillus spp. and reduced that of the pathogenic Klebsiella spp. in IUA mice. Furthermore, among intrauterine adhesion mice with diabetes, we obtained similar results to non-diabetic mice, that is, L.crispatus-pMG36e-mCXCL12 significantly improved fibrosis and inflammation in the uterine cavity of diabetic mice, and restored the vaginal microbiota balance in diabetic mice. Therefore, we speculated that vaginal administration of L. crispatus-pMG36e-mCXCL12 strains can effectively alleviate intrauterine adhesions by restoring the microbial balance and reducing inflammation and fibrosis caused by surgery.

An immunogenomic phenotype predicting behavioral treatment response: Toward precision psychiatry for mothers and children with trauma exposure

Inflammatory pathways predict antidepressant treatment non-response among individuals with major depression; yet, this phenomenon may have broader transdiagnostic and transtherapeutic relevance. Among trauma-exposed mothers (M_age = 32 years) and their young children (M_age = 4 years), we tested whether genomic and proteomic biomarkers of pro-inflammatory imbalance prospectively predicted treatment response (PTSD and depression) to an empirically-supported behavioral treatment. Forty-three mother-child dyads without chronic disease completed Child Parent Psychotherapy (CPP) for roughly 9 months. Maternal blood was drawn pre-treatment, CD14 + monocytes isolated, gene expression derived from RNA sequencing (n = 34; Illumina HiSeq 4000;TruSeqcDNA library), and serum assayed (n = 43) for C-Reactive Protein (CRP) and interleukin-1ß (IL-1ß). Symptoms of PTSD and depression decreased significantly from pre- to post-treatment for both mothers and children (all p's < 0.01). Nonetheless, a higher pre-treatment maternal pro-inflammatory imbalance of M1-like versus M2-like macrophage-associated RNA expression (M1/M2) (ß = 0.476, p = .004) and IL-1ß (ß=0.333, p = .029), but not CRP, predicted lesser improvements in maternal PTSD symptoms, unadjusted and adjusting for maternal age, BMI, ethnicity, antidepressant use, income, education, and US birth. Only higher pre-treatment M1/M2 predicted a clinically-relevant threshold of PTSD non-response among mothers (OR = 3.364, p = .015; ROC-AUC = 0.78). Additionally, higher M1/M2 predicted lesser decline in maternal depressive symptoms (ß = 0.556, p = .001), though not independent of PTSD symptoms. For child outcomes, higher maternal IL-1ß significantly predicted poorer PTSD and depression symptom trajectories (ß's = 0.318-0.429, p's < 0.01), while M1/M2 and CRP were marginally associated with poorer PTSD symptom improvement (ß's = 0.295-0.333, p's < 0.056). Pre-treatment pro-inflammatory imbalance prospectively predicts poorer transdiagnostic symptom response to an empirically-supported behavioral treatment for trauma-exposed women and their young children.

Immunomonitoring of Monocyte and Neutrophil Function in Critically Ill Patients: From Sepsis and/or Trauma to COVID-19

Immune cells and mediators play a crucial role in the critical care setting but are understudied. This review explores the concept of sepsis and/or injury-induced immunosuppression and immuno-inflammatory response in COVID-19 and reiterates the need for more accurate functional immunomonitoring of monocyte and neutrophil function in these critically ill patients. in addition, the feasibility of circulating and cell-surface immune biomarkers as predictors of infection and/or outcome in critically ill patients is explored. It is clear that, for critically ill, one size does not fit all and that immune phenotyping of critically ill patients may allow the development of a more personalized approach with tailored immunotherapy for the specific patient. In addition, at this point in time, caution is advised regarding the quality of evidence of some COVID-19 studies in the literature.

Single-Cell Transcriptomics Reveals Compartment-Specific Differences in Immune Responses and Contributions for Complement Factor 3 in Hemorrhagic Shock Plus Tissue Trauma

ABSTRACT

Hemorrhagic shock with tissue trauma (HS/T) leads to the activation of a system-wide immune-inflammatory response that involves all organs and body compartments. Recent advances in single-cell analysis permit the simultaneous assessment of transcriptomic patterns in a large number of cells making it feasible to survey the landscape of immune cell responses across numerous anatomic sites. Here, we used single-cell RNA sequencing of leukocytes from the blood, liver, and spleen to identify the major shifts in gene expression by cell type and compartment in a mouse HS/T model. At 6 h, dramatic changes in gene expression were observed across multiple-cell types and in all compartments in wild-type mice. Monocytes from circulation and liver exhibited a significant upregulation of genes associated with chemotaxis and migration and a simultaneous suppression of genes associated with interferon signaling and antigen presentation. In contrast, liver conventional DC exhibited a unique pattern compared with other myeloid cells that included a pronounced increase in major histocompatibility complex class II (MHCII) gene expression. The dominant pattern across all compartments for B and T cells was a suppression of genes associated with cell activation and signaling after HS/T. Using complement factor 3 (C3) knockout mice we unveiled a role for C3 in the suppression of monocyte Major Histocompatibility Complex class II expression and activation of gene expression associated with migration, phagocytosis and cytokine upregulation, and an unexpected role in promoting interferon-signaling in a subset of B and T cells across all three compartments after HS/T. This transcriptomic landscape study of immune cells provides new insights into the host immune response to trauma, as well as a rich resource for further investigation of trauma-induced immune responses and complement in driving interferon signaling.

Effects of 17β-Estradiol on Monocyte/Macrophage Response to Staphylococcus aureus: An In Vitro Study

To describe how 17β-estradiol (E2) influence in the monocyte/macrophage response induced by S. aureus in in vitro models of murine peritoneal macrophages (MPMs) and human peripheral blood monocytes (HPBM). MPMs (2 x 10⁵/ml) were isolated from sham (n=3) and ovariectomized (OVX) females (n = 3) and males (n = 3) after induction by thioglycolate. The MPMs obtained from OVX females and males were treated for 24 hours with 17β-estradiol (E2) (10^-7 M), and after that, inoculation with S. aureus was carried out for 6 hours. The macrophages were collected and destined to evaluate the relative gene expression of TNF-α, IL-1β, IL-6, IL-8 and TLR2. For the in vitro model of HPBMs, six men and six women of childbearing age were selected and HPBMs were isolated from samples of the volunteers’ peripheral blood. In women, blood was collected both during menstruation and in the periovulatory period. HPBMs were inoculated with S. aureus for 6 hours and the supernatant was collected for analysis of cytokines by Luminex and the HPBMs were removed for analysis of 84 genes involved in the host’s response to bacterial infections by RT-PCR array. Previous treatment with E2 decreased the gene expression and production of proinflammatory cytokines, such as TNF-α, IL-1β and IL-6 and decreased the expression of TLR2 tanto em MPMs quanto em HPBMs. The analysis of gene expression shows that E2 inhibited the NFκB pathway. It is suggested that 17β-estradiol acts as an immunoprotective in the monocyte/macrophage response induced by S. aureus.

Functional immune monitoring in severely injured patients-A pilot study

After severe trauma, the resulting excessive inflammatory response is countered by compensatory anti-inflammatory mechanisms. The systemic inflammatory response to trauma enhanced by inappropriately timed surgical second hits may be detrimental for the patient. On the other hand, overwhelming anti-inflammatory mechanisms may put patients at increased risk from secondary local and systemic infections. The ensuing sepsis and organ dysfunction due to immune dysregulation remain the leading causes of death after injury. To date, there are no clinically applicable techniques to monitor the pro-/anti-inflammatory immune status of the patients and the remaining ability to react to microbial stimuli. Therefore, in the present study, we used a highly standardized and easy-to-use system to draw peripheral whole blood from polytraumatized patients (ISS ≥ 32, n = 7) and to challenge it with bacterial lipopolysaccharide. Secreted cytokines were compared with those in samples from healthy volunteers. We observed a significant decrease in the release of monocyte-derived mediators. Surprisingly, we detected stable or even increased concentrations of cytokines related to T cell maturation and function. For clinical practicability, we reduced the incubation time before supernatants were collected. Even after an abbreviated stimulation period, a stable release of almost all analysed parameters in patient blood could be detected. In conclusion, the data are indicative of a clinically well-applicable approach to monitor the immune status in severely injured patients in a short time. This may be used to optimize the timing of necessary surgical interventions to avoid a boost of proinflammation and reduce risk of secondary infections.

Early increase in anti-inflammatory biomarkers is associated with the development of multiple organ dysfunction syndrome in severely injured trauma patients

Background

As a result of improvements in the early resuscitation phase of trauma, mortality is largely driven by later mortality due to multiple organ dysfunction syndrome (MODS), which may be mediated by an early overdrive in the host immune response. If patients at risk for MODS could be identified early, preventive treatment measures could be taken. The aim of this study is to investigate whether specific biomarkers are associated with MODS.

Methods

Multiple trauma patients presenting to the Amsterdam University Medical Centers, location Academic Medical Center, between 2012 and 2018 with an Injury Severity Score of 16 or higher were sampled on arrival at the emergency department. A wide variety of inflammatory cytokines, endothelial and lung-specific markers were determined. Comparisons were made between patients with and without MODS. Univariate and multivariate logistic regression was used to determine associations between specific biomarkers and MODS. A p value of 0.05 was considered to be statistically significant.

Results

In total, 147 multiple trauma patients were included. Of these, 32 patients developed MODS (21.7%). Patients who developed MODS were more severely injured, had more traumatic brain injury and showed more deranged markers of coagulation when compared with patients without MODS. Overall, both proinflammatory and anti-inflammatory cytokines were higher in patients with MODS, indicative of a host immune reaction. In the multivariate analysis, the combination of anti-inflammatory proteins interleukin 1 receptor antagonist (IL-1RA) (OR 1.27 (1.07–1.51), p=0.002) and Clara cell protein 16 (CC-16) (1.06 (1.01–1.05), p=0.031) was most strongly associated with the development MODS.

Conclusions

In trauma, anti-inflammatory proteins IL-1RA and CC-16 have the potential to early identify patients at risk for development of MODS. Further research is warranted to prospectively validate these results.

Level of evidence

Prognostic study, level III.

Trauma-Induced Long-Term Alterations of Human T Cells and Monocytes-Results of an Explorative, Cross-Sectional Study

BACKGROUND

Major trauma leads to complex immune reactions, known to result in a transient immunodeficiency. The long-term consequences of severe trauma on immune function and regulation as well as its clinical impact remain unclear.

METHODS

Six months (ranging from -12 to +5 days) after a major trauma event, 12 former trauma patients (Injury Severity Score ≥ 16) and 12 healthy volunteers were enrolled. The current clinical status and infection history since discharge were assessed by a standardized questionnaire. Immune cell subsets (cluster of differentiation (CD)4, CD8, CD14), cell surface receptor expression (programmed cell death protein 1 (PD-1), B- and T-lymphocyte attenuator (BTLA), cytotoxic T-lymphocyte-associated protein 4, toll-like receptor (TLR)-2, -4, and -5, Dectin-1, programmed death ligand 1 (PD-1L)), and human leucocyte antigen D-related receptor (HLA-DR)-expression were quantified by flow cytometry. Cytokine secretion (IL-2, -4, -6, -10, and 17A, tumor necrosis factor (TNF)-α, and interferon (IFN)-γ) was assessed after stimulation of whole blood with LPS-, α-CD3/28, or zymosan.

RESULTS

Analysis of surface receptors on T cells revealed a significant elevation of PD-1 expression on CD4 T cells, whereas BTLA expression on CD4 and CD8 T cells was significantly suppressed in the trauma cohort. Monocytes showed a significantly reduced expression of TLR-2 and -4 as well as a reduced proportion of TLR-4 monocytes. HLA-DR receptor density revealed no significant changes between both cohorts. LPS-induced IL-6 and TNF-α secretion showed non-significant trends toward reduced values. No differences regarding clinical apparent infections could be detected.

CONCLUSIONS

Six months following major trauma, changes of cell surface receptors on CD4 and CD8 T cells as well as on CD14 monocytes were present, hinting toward an immunosuppressive phenotype. Following major trauma, although IL-6 and TNF-α release after stimulation were reduced, they did not reach statistical significance. Overall, further studies are necessary to evaluate the clinical implications of these findings.

TRIAL REGISTRATION

DRKS00009876, Internet Portal of the German Clinical Trials Register (DRKS), registration date 11.08.2016, https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00009876.

Reduced NLRP3 Gene Expression Limits the IL-1β Cleavage via Inflammasome in Monocytes from Severely Injured Trauma Patients

Objective

Traumatic injury or severe surgery leads to a profound immune response with a diminished functionality of monocytes and subsequently their IL-1β release. IL-1β plays an important role in host immunity and protection against infections. Its biological activation via IL-1β-precursor processing requires the transcription of inflammasome components and their activation. Deregulated activity of NOD-like receptor inflammasomes (NLR) like NLRP3 that leads to the maturation of IL-1β has been described in various diseases. While the role of other inflammasomes has been studied in monocytes, nothing is known about NLRP3 inflammasome after a traumatic injury. Here, the role of the NLRP3 inflammasome in impaired monocyte functionality after a traumatic injury was analyzed.

Measurements and Main Results

Ex vivo-in vitro stimulation of isolated CD14⁺ monocytes with lipopolysaccharide (LPS) showed a significantly higher IL-1β secretion in healthy volunteers (HV) compared to trauma patients (TP) after admission. Reduced IL-1β secretion was paralleled by significantly lowered gene expression of NLRP3 in monocytes from TP compared to those of HV. Transfection of monocytes with NLRP3-encoding plasmid recovered the functionality of monocytes from TP regarding the IL-1β secretion.

Conclusions

This study demonstrates that CD14⁺ monocytes from TP are significantly diminished in their function and that the presence of NLRP3 components is necessary in recovering the ability of monocytes to produce active IL-1β. This recovery of the NLRP3 inflammasome in monocytes may imply a new target for treatment and therapy of immune suppression after severe injury.

Comparative Analysis of the Regulatory T Cells Dynamics in Peripheral Blood in Human and Porcine Polytrauma

Background

Severely injured patients experience substantial immunological stress in the aftermath of traumatic insult, which often results in systemic immune dysregulation. Regulatory T cells (Treg) play a key role in the suppression of the immune response and in the maintenance of immunological homeostasis. Little is known about their presence and dynamics in blood after trauma, and nothing is known about Treg in the porcine polytrauma model. Here, we assessed different subsets of Treg in trauma patients (TP) and compared those to either healthy volunteers (HV) or data from porcine polytrauma.

Methods

Peripheral blood was withdrawn from 20 TP with injury severity score (ISS) ≥16 at the admittance to the emergency department (ED), and subsequently on day 1 and at day 3. Ten HV were included as controls (ctrl). The porcine polytrauma model consisted of a femur fracture, liver laceration, lung contusion, and hemorrhagic shock resulting in an ISS of 27. After polytrauma, the animals underwent resuscitation and surgical fracture fixation. Blood samples were withdrawn before and immediately after trauma, 24 and 72 h later. Different subsets of Treg, CD4+CD25+, CD4+CD25+FoxP3+, CD4+CD25+CD127-, and CD4+CD25+CD127-FoxP3+ were characterized by flow cytometry.

Results

Absolute cell counts of leukocytes were significantly increasing after trauma, and again decreasing in the follow-up in human and porcine samples. The proportion of human Treg in the peripheral blood of TP admitted to the ED was lower when compared to HV. Their numbers did not recover until 72 h after trauma. Comparable data were found for all subsets. The situation in the porcine trauma model was comparable with the clinical data. In porcine peripheral blood before trauma, we could identify Treg with the typical immunophenotype (CD4+CD25+CD127-), which were virtually absent immediately after trauma. Similar to the human situation, most of these cells expressed FoxP3, as assessed by intracellular FACS stain.

Conclusion

Despite minor percental differences in the recovery of Treg populations after trauma, our findings show a comparable decrease of Treg early after polytrauma, and strengthen the immunological significance of the porcine polytrauma model. Furthermore, the Treg subpopulation CD4+CD25+CD127- was characterized in porcine samples.

Toll-Like Receptors 2 and 4 Predict New-Onset Atrial Fibrillation in Acute Myocardial Infarction Patients

Myocardial infarction (MI) can cause new-onset atrial fibrillation (AF) due to cardiac remodeling. As a recent study has shown, inflammatory factors are closely tied to cell death and survival in myocardial ischemia injury. Toll-like receptors (TLRs) have been shown to participate in the process of myocardial infarction as innate immune factors.The subjects were divided into 3 groups: healthy controls (n = 82), MI patients (n = 84), and AFMI (new-onset atrial fibrillation after myocardial infarction) patients (n = 85). Peripheral blood mononuclear cell (PBMC) TLR mRNA expression was detected by rt-PCR. Western blot was used to analyze PBMC TLRs and their downstream signal protein expression. PBMCs were presented as TLR2 expression or TLR4 expression using flow cytometry.From mRNA to protein detection, PBMC TLR2 and TLR4 were significantly higher in the AFMI group than in the control group and MI group. A similar tendency was also observed in the expression of downstream signaling proteins. When further analyzed with TLR2 and TLR4 antibodies by flow cytometry, PBMC levels also appeared to be higher in AFMI patients than those in MI patients and the healthy control group.In our study, PBMC TLRs and their downstream signaling proteins were significantly higher in the acute myocardial infarction patients with new-onset atrial fibrillation compared with healthy people and acute myocardial infarction patients without new-onset atrial fibrillation. They have the potential to be novel biomarkers for new-onset atrial fibrillation after acute myocardial infarction.

Early decreased TLR2 expression on monocytes is associated with their reduced phagocytic activity and impaired maturation in a porcine polytrauma model

In their post-traumatic course, trauma patients suffering from multiple injuries have a high risk for immune dysregulation, which may contribute to post-injury complications and late mortality. Monocytes as specific effector cells of the innate immunity play a crucial role in inflammation. Using their Pattern Recognition Receptors (PRRs), notably Toll-Like Receptors (TLR), the monocytes recognize pathogens and/or pathogen-associated molecular patterns (PAMPs) and organize their clearance. TLR2 is the major receptor for particles of gram-positive bacteria, and initiates their phagocytosis. Here, we investigated the phagocytizing capability of monocytes in a long-term porcine severe trauma model (polytrauma, PT) with regard to their TLR2 expression. Polytrauma consisted of femur fracture, unilateral lung contusion, liver laceration, hemorrhagic shock with subsequent resuscitation and surgical fracture fixation. After induction of PT, peripheral blood was withdrawn before (-1 h) and directly after trauma (0 h), as well as 3.5 h, 5.5 h, 24 h and 72 h later. CD14+ monocytes were identified and the expression levels of H(S)LA-DR and TLR2 were investigated by flow cytometry. Additionally, the phagocytizing activity of monocytes by applying S. aureus particles labelled with pHrodo fluorescent reagent was also assessed by flow cytometry. Furthermore, blood samples from 10 healthy pigs were exposed to a TLR2-neutralizing antibody and subsequently to S. aureus particles. Using flow cytometry, phagocytizing activity was determined. P below 0.05 was considered significant. The number of CD14+ monocytes of all circulating leukocytes remained constant during the observational time period, while the percentage of CD14+H(S)LA-DR+ monocytes significantly decreased directly, 3.5 h and 5.5 h after trauma. The percentage of TLR2+ expressing cells out of all monocytes significantly decreased directly, 3.5 h and 5.5 h after trauma. The percentage of phagocytizing monocytes decreased immediately and remained lower during the first 3.5 h after trauma, but increased after 24 h. Antagonizing TLR2 significantly decreased the phagocytizing activity of monocytes. Both, decreased percentage of activated as well as TLR2 expressing monocytes persisted as long as the reduced phagocytosis was observed. Moreover, neutralizing TLR2 led to a reduced capability of phagocytosis as well. Therefore, we assume that reduced TLR2 expression may be responsible for the decreased phagocytizing capacity of circulating monocytes in the early post-traumatic phase.