Toll-like receptor 2 downregulation and cytokine dysregulation predict mortality in patients with Staphylococcus aureus bacteremia

An Update on Toll-like Receptor 2, Its Function and Dimerization in Pro- and Anti-Inflammatory Processes

While a certain level of inflammation is critical for humans to survive infection and injury, a prolonged inflammatory response can have fatal consequences. Pattern recognition Toll-like receptors (TLRs) are key players in the initiation of an inflammatory process. TLR2 is one of the most studied pattern recognition receptors (PRRs) and is known to form heterodimers with either TLR1, TLR4, TLR6, and TLR10, allowing it to recognize a wide range of pathogens. Although a large number of studies have been conducted over the past decades, there are still many unanswered questions regarding TLR2 mechanisms in health and disease. In this review, we provide an up-to-date overview of TLR2, including its homo- and heterodimers. Furthermore, we will discuss the pro- and anti-inflammatory properties of TLR2 and recent findings in prominent TLR2-associated infectious and neurodegenerative diseases.

Anti-Alpha-Toxin Antibody Responses and Clinical Outcomes of Staphylococcus aureus Bacteremia

BACKGROUND

Alpha-toxin (AT), a major virulence factor of Staphylococcus aureus, is an important immunotherapeutic target to prevent or treat invasive S. aureus infections. Previous studies have suggested that anti-AT antibodies (Abs) may have a protective role against S. aureus bacteremia (SAB), but their function remains unclear. Therefore, we aimed to investigate the association between serum anti-AT Ab levels and clinical outcomes of SAB.

METHODS

Patients from a prospective SAB cohort at a tertiary-care medical center (n = 51) were enrolled in the study from July 2016 to January 2019. Patients without symptoms or signs of infection were enrolled as controls (n = 100). Blood samples were collected before the onset of SAB and at 2- and 4-weeks post-bacteremia. Anti-AT immunoglobin G (IgG) levels were measured using an enzyme-linked immunosorbent assay. All clinical S. aureus isolates were tested for the presence of hla using polymerase chain reaction.

RESULTS

Anti-AT IgG levels in patients with SAB before the onset of bacteremia did not differ significantly from those in non-infectious controls. Pre-bacteremic anti-AT IgG levels tended to be lower in patients with worse clinical outcomes (7-day mortality, persistent bacteremia, metastatic infection, septic shock), although the differences were not statistically significant. Patients who needed intensive care unit care had significantly lower anti-AT IgG levels at 2 weeks post-bacteremia (P = 0.020).

CONCLUSION

The study findings suggest that lower anti-AT Ab responses before and during SAB, reflective of immune dysfunction, are associated with more severe clinical presentations of infection.

Effects of 5α-dihydrotestosterone on the modulation of monocyte/macrophage response to Staphylococcus aureus: an in vitro study

BACKGROUND

Staphylococcus aureus (S. aureus) is a pathogen responsible for a wide range of clinical manifestations and potentially fatal conditions. There is a paucity of information on the influence of androgens in the immune response to S. aureus infection. In this study, we evaluated the influence of the hormone 5α-dihydrotestosterone (DHT) on mouse peritoneal macrophages (MPMs) and human peripheral blood monocytes (HPBMs) induced by S. aureus.

METHODS

An in vitro model of MPMs from BALB/c sham males, orchiectomised (OQX) males, and females was used. Cells were inoculated with 10 μL of S. aureus, phage-type 80 or sterile saline (control) for 6 h. The MPMs of OQX males and females were pre-treated with 100 μL of 10^-2 M DHT for 24 h before inoculation with S. aureus. The concentration of the cytokines TNF-α, IL-1α, IL-6, IL-8, and IL-10; total nitrites (NO^-2); and hydrogen peroxide (H₂O₂) were measured in the supernatant of MPM cultures. In addition, the toll-like receptor 2 (TLR2) and nuclear factor kappa B (NF-kB) genes that are involved in immune responses were analysed. For the in vitro model of HPBMs, nine men and nine women of childbearing age were selected and HPBMs were isolated from samples of the volunteers' peripheral blood. In women, blood was collected during the periovulatory period. The HPBMs were inoculated with S. aureus for 6 h and the supernatant was collected for the analysis of cytokines TNF-α, IL-6, IL-12; and GM-CSF, NO^-2, and H₂O₂. The HPBMs were then removed for the analysis of 84 genes involved in the host's response to bacterial infections by RT-PCR array. GraphPad was used for statistical analysis with a p value < 0.05.

RESULTS

Our data demonstrated that MPMs from sham males inoculated with S. aureus displayed higher concentrations of inflammatory cytokines and lower concentrations of IL-10, NO^-2, and H₂O₂ when compared with MPMs from OQX males and females. A similar result was observed in the HPBMs of men when compared with those of women. Previous treatment with DHT in women HPBMs increased the production of pro-inflammatory cytokines and decreased the levels of IL-10, NO^-2, and H₂O₂. The analysis of gene expression showed that DHT increased the activity of the TLR2 and NF-kB pathways in both MPMs and HPBMs.

CONCLUSIONS

We found that DHT acts as an inflammatory modulator in the monocyte/macrophage response induced by S. aureus and females exhibit a better immune defence response against this pathogen.

TLR2 and TLR4 activity in monocytes and macrophages after exposure to amoxicillin, ciprofloxacin, doxycycline and erythromycin

BACKGROUND

Antibiotics are used to treat bacterial infections but also impact immunity. This is usually attributed to antibiotic-induced dysbiosis of the microbiota, but antibiotics may have a direct effect on immune cells and immunity-associated receptors, such as Toll-like receptors (TLRs).

OBJECTIVES

To investigate whether antibiotics alter TLR2/1, TLR2/6 and TLR4 activity in immune cells.

METHODS

We evaluated the effects of amoxicillin, ciprofloxacin, doxycycline and erythromycin on TLR2/1-, TLR2/6- and TLR4-induced NF-κB activation in THP1-XBlue™-MD2-CD14 cells. Furthermore, we studied TNF-α and IL-6 levels in THP-1-derived macrophages after exposure to these antibiotics and TLR ligands.

RESULTS

Amoxicillin had no effect on any of the TLRs studied. However, ciprofloxacin reduced TLR2/1, TLR2/6 and TLR4 activity in THP1-XBlue™-MD2-CD14 cells and decreased TLR2/1-induced TNF-α and IL-6 in macrophages. Doxycycline reduced TLR2/6 and TLR4 activity in THP1-XBlue™-MD2-CD14 cells and TNF-α and IL-6 levels in response to TLR2/6 stimulation in macrophages. Erythromycin decreased TLR2/1 and TLR4 activity in THP1-XBlue™-MD2-CD14 cells without changes in TNF-α and IL-6 levels in macrophages. In addition, ciprofloxacin decreased the expression of TLR2 mRNA.

CONCLUSIONS

These results suggest that some antibiotics may attenuate TLR-dependent monocyte/macrophage responses and likely reduce bacterial clearance. The latter is particularly important in infections with AMR bacteria, where misprescribed antibiotics not only fail in control of AMR infections but might also weaken host defence mechanisms by limiting innate immune responses. Our data suggest that efforts should be made to prevent the deterioration of the immune response during and after antibiotic treatment.

What Is the Optimal Follow-up Length for Mortality in Staphylococcus aureus Bacteremia? Observations From a Systematic Review of Attributable Mortality

Background

Deaths following Staphylococcus aureus bacteremia (SAB) may be related or unrelated to the infection. In SAB therapeutics research, the length of follow-up should be optimized to capture most attributable deaths and minimize nonattributable deaths. We performed a secondary analysis of a systematic review to describe attributable mortality in SAB over time.

Methods

We systematically searched Medline, Embase, and Cochrane Database of Systematic Reviews from 1 January 1991 to 7 May 2021 for human observational studies of SAB. To be included in this secondary analysis, the study must have reported attributable mortality. Two reviewers extracted study data and assessed risk of bias independently. Pooling of study estimates was not performed due to heterogeneity in the definition of attributable deaths.

Results

Twenty-four observational cohort studies were included. The median proportion of all-cause deaths that were attributable to SAB was 77% (interquartile range [IQR], 72%–89%) at 1 month and 62% (IQR, 58%–75%) at 3 months. At 1 year, this proportion was 57% in 1 study. In 2 studies that described the rate of increase in mortality over time, 2-week follow-up captured 68 of 79 (86%) and 48 of 57 (84%) attributable deaths that occurred by 3 months. By comparison, 1-month follow-up captured 54 of 57 (95%) and 56 of 60 (93%) attributable deaths that occurred by 3 months in 2 studies.

Conclusions

The proportion of deaths that are attributable to SAB decreases as follow-up lengthens. Follow-up duration between 1 and 3 months seems optimal if evaluating processes of care that impact SAB mortality.

Clinical Trials Registration

PROSPERO CRD42021253891.

Does SARS-CoV-2 affect neurodegenerative disorders? TLR2, a potential receptor for SARS-CoV-2 in the CNS

The coronavirus (COVID-19) pandemic, caused by severe acute respiratory system coronavirus 2 (SARS-CoV-2), has created significant challenges for scientists seeking to understand the pathogenic mechanisms of SARS-CoV-2 infection and to identify the best therapies for infected patients. Although ACE2 is a known receptor for the virus and has been shown to mediate viral entry into the lungs, accumulating reports highlight the presence of neurological symptoms resulting from infection. As ACE2 expression is low in the central nervous system (CNS), these neurological symptoms are unlikely to be caused by ACE2-virus binding. In this review, we will discuss a proposed interaction between SARS-CoV-2 and Toll-like receptor 2 (TLR2) in the CNS. TLR2 is an innate immune receptor that recognizes exogenous microbial components but has also been shown to interact with multiple viral components, including the envelope (E) protein of SARS-CoV-2. In addition, TLR2 plays an important role in the pathogenesis of neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD). Based on these observations, we hypothesize that TLR2 may play a critical role in the response to SARS-CoV-2 infiltration in the CNS, thereby resulting in the induction or acceleration of AD and PD pathologies in patients.

Development of a Conserved Chimeric Vaccine for Induction of Strong Immune Response against Staphylococcus aureus Using Immunoinformatics Approaches

Staphylococcus aureus is one of the most notorious Gram-positive bacteria with a very high mortality rate. The WHO has listed S. aureus as one of the ESKAPE pathogens requiring urgent research and development efforts to fight against it. Yet there is a major layback in the advancement of effective vaccines against this multidrug-resistant pathogen. SdrD and SdrE proteins are attractive immunogen candidates as they are conserved among all the strains and contribute specifically to bacterial adherence to the host cells. Furthermore, these proteins are predicted to be highly antigenic and essential for pathogen survival. Therefore, in this study, using the immunoinformatics approach, a novel vaccine candidate was constructed using highly immunogenic conserved T-cell and B-cell epitopes along with specific linkers, adjuvants, and consequently modeled for docking with human Toll-like receptor 2. Additionally, physicochemical properties, secondary structure, disulphide engineering, and population coverage analysis were also analyzed for the vaccine. The constructed vaccine showed good results of worldwide population coverage and a promising immune response. For evaluation of the stability of the vaccine-TLR-2 docked complex, a molecular dynamics simulation was performed. The constructed vaccine was subjected to in silico immune simulations by C-ImmSim and Immune simulation significantly provided high levels of immunoglobulins, T-helper cells, T-cytotoxic cells, and INF-γ. Lastly, upon cloning, the vaccine protein was reverse transcribed into a DNA sequence and cloned into a pET28a (+) vector to ensure translational potency and microbial expression. The overall results of the study showed that the designed novel chimeric vaccine can simultaneously elicit humoral and cell-mediated immune responses and is a reliable construct for subsequent in vivo and in vitro studies against the pathogen.