A bedaquiline, pyrazinamide, levofloxacin, linezolid, clofazimine second line regimen for tuberculosis displays similar early bactericidal activity as the standard rifampin based first line regimen.

BACKGROUND: In 2018 the World Health Organization (WHO) recommended a switch to an all oral bedaquiline based second line regimen for treatment of drug resistant (DR) tuberculosis (TB). How these new second line regimens fare in comparison to first line regimens for treatment of drug sensitive (DS) tuberculosis is not well known. METHODS: In this study, we contemporaneously enrolled subjects with DS (n = 31) and DR (n = 23) TB and assessed their response to therapy with first-line (rifampin, isoniazid, ethambutol, pyrazinamide) or second-line (bedaquiline, pyrazinamide, levofloxacin, linezolid, clofazimine) regimens, respectively. RESULTS: We found that the early bactericidal activity of first and second line regimens was similar during the first two weeks of therapy as determined by BACTEC MGIT, colony forming units (CFU), and a liquid limiting dilution (LD) assays capable of detecting differentially detectable/culturable Mtb (DD Mtb). Further, an identical percentage (77.8%) of subjects from the DS and DR cohorts converted to culture negative after two months of therapy. CONCLUSIONS: Despite presenting with more advanced disease at time of treatment, subjects with DR TB receiving an all oral bedaquiline based second line treatment regimen displayed a similar microbiological response to therapy as subjects with DS TB receiving a first-line treatment regimen.

Transcriptional Biomarkers of Differentially Detectable Mycobacterium tuberculosis in Patient Sputum.

Certain populations of Mycobacterium tuberculosis go undetected by standard diagnostics but can be enumerated using limiting dilution assays. These differentially detectable M. tuberculosis (DD M. tuberculosis) populations may have relevance for persistence due to their drug tolerance. It is unclear how well DD M. tuberculosis from patients is modeled by a recently developed in vitro model in which M. tuberculosis starved in phosphate-buffered saline is incubated with rifampin to produce DD M. tuberculosis (the PBS-RIF model). This study attempted to answer this question. We selected 14 genes that displayed differential expression in the PBS-RIF model and evaluated their expression in patient sputa containing various proportions of DD M. tuberculosis. The expression of 12/14 genes correlated with the relative abundance of DD M. tuberculosis in patient sputa. Culture filtrate (CF), which promotes recovery of DD M. tuberculosis from certain patient sputa, improved these correlations in most cases. The gene whose reduced expression relative to M. tuberculosis 16S rRNA showed the greatest association with the presence and relative abundance of DD M. tuberculosis in patient sputa, icl1, was recently shown to play a functional role in restraining DD M. tuberculosis formation in the PBS-RIF model. Expression of icl1, combined with two additional DD M. tuberculosis-related genes, showed strong performance for predicting the presence or absence of DD M. tuberculosis in patient sputa (receiver operating characteristic [ROC] area under the curve [AUC] = 0.88). Thus, the in vitro DD M. tuberculosis model developed by Saito et al. (K. Saito, T. Warrier, S. Somersan-Karakaya, L. Kaminski, et al., Proc Natl Acad Sci U S A 114:E4832-E4840, 2017, https://doi.org/10.1073/pnas.1705385114) bears a resemblance to DD M. tuberculosis found in tuberculosis (TB) patients, and DD M. tuberculosis transcriptional profiles may be useful for monitoring DD M. tuberculosis populations in patient sputum. IMPORTANCE Differentially detectable M. tuberculosis (DD M. tuberculosis), which is detectable by limiting dilution assays but not by CFU, is present and enriched for in TB patient sputum after initiation of first-line therapy. These cryptic cells may play a role in disease persistence due to their phenotypic tolerance to anti-TB drugs. A recently developed in vitro model of DD M. tuberculosis (the PBS-RIF model) has expanded our understanding of these cells, though how well it translates to DD M. tuberculosis in patients is currently unknown. To answer this question, we selected 14 genes that displayed differential expression in the PBS-RIF model and evaluated their expression in TB patient sputa. We found that 12/14 of these genes showed a similar expression profile in patient sputa that correlated with the relative abundance of DD M. tuberculosis. Further, the expression of three of these genes showed strong performance for predicting the presence or absence of DD M. tuberculosis in patient sputa. The use of DD M. tuberculosis transcriptional profiles may allow for easier monitoring of DD M. tuberculosis populations in patient sputum in comparison to limiting dilution assays.

An optimized method for purifying, detecting and quantifying Mycobacterium tuberculosis RNA from sputum for monitoring treatment response in TB patients.

Diagnostics that more accurately detect and quantify viable Mycobacterium tuberculosis (Mtb) in the sputum of patients undergoing therapy are needed. Current culture- and molecular-based tests have shown limited efficacy for monitoring treatment response in TB patients, either due to the presence of viable sub-populations of Mtb which fail to grow under standard culture conditions (termed differentially detectable/culturable Mtb, DD Mtb) or the prolonged half-life of Mtb DNA in sputum. Here, we report an optimized RNA-based method for detecting and quantifying viable Mtb from patient sputum during the course of therapy. We first empirically derived a novel RNA extraction protocol from sputum that improves recovery of Mtb RNA while almost completely eliminating contamination from Mtb DNA and host nucleic acids. Next, we identified five Mtb 16S rRNA primer sets with varying limits of detection that were capable of distinguishing between live versus dead H37Rv Mtb. This combined protocol was then tested on sputa from a longitudinal cohort of patients receiving therapy for drug sensitive (DS) or drug resistant (DR) TB with first-line or second-line regimens, respectively. Results were compared with that of culture, including CFU, BACTEC MGIT, and a limiting dilution assay capable of detecting DD Mtb. The five 16S rRNA primer sets positively identified nearly all (range 94-100%) culture positive sputa, and a portion (19-37%) of culture negative sputa. In comparison, ten highly expressed Mtb mRNAs showed positivity in 72-86% of culture positive sputa, and in 0-13% of culture negative sputa. Two of the five 16S rRNA primer sets were able to positively identify 100% of culture positive sputa, and when tested on culture negative sputa from the DS cohort at 2 months post-initiation of therapy, identified 40% of samples as positive; a percentage that is in line with expected treatment failure rates when first-line therapy is discontinued early. These two primer sets also detected 16S rRNA in 13-20% of sputa at 6 months post-initiation of therapy in the DR cohort. Cycle threshold values for 16S rRNA showed a strong correlation with Mtb numbers as determined by culture (R > 0.87), including as Mtb numbers declined during the course of treatment with first-line and second-line regimens. The optimized molecular assay outlined here may have utility for monitoring treatment response in TB patients.

Developing Molecular Surveillance Capacity for Asymptomatic and Drug-Resistant Malaria in a Resource-Limited Setting-Experiences and Lessons Learned.

The COVID-19 pandemic has highlighted the important role molecular surveillance plays in public health. Such capacity however is either weak or nonexistent in many low-income countries. This article outlines a 2-year effort to establish two high-throughput molecular surveillance laboratories in Myanmar for tracking asymptomatic and drug resistant Plasmodium falciparum malaria. The lessons learned from this endeavor may prove useful for others seeking to establish similar molecular surveillance capacity in other resource-limited settings.

Rapid Emergence and Spread of Severe Acute Respiratory Syndrome Coronavirus 2 Gamma (P.1) Variant in Haiti.

After an initial wave of coronavirus disease 2019 (COVID-19) in Haiti in summer 2020 (primarily lineage B.1), seropositivity for anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) immunoglobulin G (IgG) was ~40%. Variant P.1 (gamma) was introduced in February 2021, with an initially limited introduction followed by exponential local dissemination within this unvaccinated population with prior exposure to earlier SARS-CoV-2 lineages.

Characterization of Differentially Detectable Mycobacterium tuberculosis in the Sputum of Subjects with Drug-Sensitive or Drug-Resistant Tuberculosis before and after Two Months of Therapy.

Standard methods for enumerating Mycobacterium tuberculosis in patient sputum can miss large populations of viable M. tuberculosis cells that are unable to grow either on solid medium or in liquid medium unless the medium has been extensively diluted. Because these bacteria can be detected in liquid medium after limiting dilution, they have been termed differentially culturable or differentially detectable M. tuberculosis (DD-Mtb). Treatment with isoniazid (H), rifampin (R), pyrazinamide (Z), and ethambutol (E) (HRZE) for 1 to 2 weeks has been shown to increase the representation of DD-Mtb in the sputum of drug-sensitive (DS) tuberculosis (TB) patients. However, little is known about DD-Mtb after longer periods of treatment with HRZE or in patients with drug-resistant (DR) TB who receive second-line therapies. Here, we measured the proportion of DD-Mtb cells in the sputum of 47 subjects, 29 with DS TB and 18 with DR TB, before initiation of treatment and at 2 weeks and 2 months thereafter. Prior to treatment, DD-Mtb cells represented the majority of M. tuberculosis cells in the sputum of 21% of subjects with DS TB, and this proportion rose to 65% after 2 weeks of treatment with first-line drugs. In subjects with DR TB, DD-Mtb cells were found in the sputum of 29% of subjects prior to treatment initiation, and this proportion remained steady at 31% after 2 weeks of treatment with second-line drugs. By 2 months, DD-Mtb cells were detected in the sputum of only 2/15 (13.3%) subjects with DS TB and in 0/15 of subjects with DR TB. One of the DS subjects whose sputum was positive for DD-Mtb at month 2 later experienced treatment failure.

Ultrasensitive Diagnostics for Low-Density Asymptomatic Plasmodium falciparum Infections in Low-Transmission Settings.

The emergence of multidrug-resistant Plasmodium falciparum malaria in Southeast Asia (SEA) has accelerated regional malaria elimination efforts. Most malaria in this and other low-transmission settings exists in asymptomatic individuals, which conventional diagnostic tests lack the sensitivity to detect. This has led to the development of new ultrasensitive diagnostics that are capable of detecting these low-parasitemia infections. This review summarizes the current status of ultrasensitive technologies, including PCR and loop-mediated isothermal amplification (LAMP)-based methods, as well as a newly developed ultrasensitive rapid diagnostic test (uRDT). The sensitivity, specificity, and field performance of these platforms will be examined, as well as their suitability for use in resource-limited settings to aid in malaria elimination efforts. uRDTs, with their improved sensitivity, are now able to detect approximately half of asymptomatic infections, providing a useful point-of-contact tool for malaria surveillance. The increased sensitivity and high-throughput nature of PCR-based tests make them ideal for screening large populations in places where laboratory capacity exists, and the recent commercialization of malaria LAMP kits should facilitate their adoption as a public health tool in places where such infrastructure is lacking. Finally, recent advances with dried blood spots may enable utilization of the extensive laboratory infrastructure of higher-income countries to assist with molecular surveillance in support of malaria elimination. If malaria is to be eliminated in SEA and other low-endemicity regions, then ultrasensitive diagnostics will likely play a key role in identifying and clearing the vast asymptomatic pool of infections that are common to these regions.

An improved nucleic acid extraction method from dried blood spots for amplification of Plasmodium falciparum kelch13 for detection of artemisinin resistance.

BACKGROUND: Mutational analysis of the Plasmodium falciparum kelch 13 (k13) gene is routinely performed to track the emergence and spread of artemisinin resistance. Surveillance of resistance markers has been impeded by the difficulty of extracting sufficient DNA from low parasite density infections common in low-transmission settings, such as Southeast Asia. This problem can be overcome by collecting large volumes of venous blood. Efficient methods for extracting and amplifying k13 from dried blood spots (DBS) would facilitate resistance surveillance. METHODS: Methods for k13 amplification from standard Whatman 3MM DBS (stored for 14 days at 28 °C with 80% relative humidity) were optimized by systematically testing different extraction conditions. Conditions that improved parasite DNA recovery as assessed by quantitative polymerase chain reaction (PCR) of 18S rDNA were then tested for their impact on k13 PCR amplification. RESULTS: The optimized protocol for amplification of k13 from DBS is markedly more sensitive than standard methods using commercial kits. Using this method, k13 was successfully amplified from laboratory-created DBS samples with parasite densities as low as 500 parasites/mL. Importantly, the method recovers both DNA and RNA, making it compatible with RNA-based ultrasensitive techniques currently in use. CONCLUSIONS: The optimized DBS protocol should facilitate drug resistance surveillance, especially in low-transmission settings where clinical malaria infections with high parasite densities are rare.

Drugs targeting SIRT1, a new generation of therapeutics for osteoporosis and other bone related disorders?

With an aging population and limited treatment options, osteoporosis currently represents a significant public health challenge. Recent animal studies indicate that longevity-associated SIRT1 may serve as an attractive pharmacological target for the treatment of osteoporosis and other bone related disorders. Pre-clinical studies demonstrate that mice treated with SIRT1 agonists show protection against age-related, post-menopausal, and disuse models of osteoporosis. Conversely, SIRT1 knockout models display low bone mass phenotypes associated with increased bone resorption and decreased bone formation. This review summarizes recent animal and human experimental data showing that pharmacological activation of SIRT1 may act in a manner that current treatments do not, namely by treating the imbalance in bone remodeling that is the root cause of osteoporosis and other bone disorders.

An efficient and cost-effective method for purification of small sized DNAs and RNAs from human urine.

Urine holds great promise as a non-invasive sampling method for molecular diagnostics. The cell-free nucleic acids of urine however are small, labile, and difficult to purify. Here an efficient method for the purification of these nucleic acids is presented. An empirically derived protocol was devised by first identifying conditions that allowed recovery of a 100 base pair (bp) DNA, followed by optimization using a quantitative polymerase chain reaction (qPCR) assay. The resulting method efficiently purifies both small sized DNAs and RNAs from urine, which when combined with quantitative reverse transcription PCR (qRTPCR), demonstrably improves detection sensitivity. Fractionation experiments reveal that nucleic acids in urine exist both in the cell-free and cellular fraction, roughly in equal proportion. Consistent with previous studies, amplicons > 180bp show a marked loss in PCR sensitivity for cell-free nucleic acids. Finally, the lysis buffer developed here also doubles as an effective preservative, protecting against nucleic acid degradation for at least two weeks under simulated field conditions. With this method, volumes of up to 25ml of whole urine can be purified in a high-throughput and cost-effective manner. Coupled with its ability to purify both DNA and RNA, the described method may have broad applicability for improving the diagnostic utility of urine, particularly for the detection of low abundant targets.

The variable role of SIRT1 in the maintenance and differentiation of mesenchymal stem cells.

SIRT1 is an NAD+-dependent deacetylase that acts as a nutrient sensitive regulator of longevity. SIRT1 also acts as a key regulator of mesenchymal stem cells (MSCs), adult stem cells that give rise to tissues such as bone, fat, muscle and cartilage. This review focuses on how SIRT1 regulates the self-renewal, multipotency and differentiation of MSCs. The variable role of SIRT1 in promoting the differentiation of MSCs towards certain lineages, while repressing others, will be examined within the broader context of aging, calorie restriction, and regenerative medicine. Finally, recent animal and human studies will be highlighted which paint an overall salutary role for SIRT1 in protecting MSCs (and resulting tissues) from age-related atrophy and dysfunction.

A brief history of modern aging research.

Over the last few decades, aging research has emerged as a vibrant area of rigorous scientific study. With its humble beginnings in yeast and worms, the field has progressed so dramatically that scientists are now able to extend the lifespan of mice with the use of small molecule drugs. However, it was not too long ago that answering the more basic question, whether aging was amenable to scientific study, was itself a topic of contentious debate. To begin to understand how a field that was initially thought of as pseudoscience has come so far, it is instructive to understand its roots in both theory and practice.

SIRT1 is a positive regulator of in vivo bone mass and a therapeutic target for osteoporosis.

Overexpression or pharmacological activation of SIRT1 has been shown to extend the lifespan of mice and protect against aging-related diseases. Here we show that pharmacological activation of SIRT1 protects in two models of osteoporosis. Ovariectomized female mice and aged male mice, models for post-menopausal and aging-related osteoporosis, respectively, show significant improvements in bone mass upon treatment with SIRT1 agonist, SRT1720. Further, we find that calorie restriction (CR) results in a two-fold upregulation of sirt1 mRNA expression in bone tissue that is associated with increased bone mass in CR mice. Reciprocally, SIRT1 whole-body knockout (KO) mice, as well as osteoblast and osteoclast specific KOs, show a low bone mass phenotype; though double knockout mice (containing SIRT1 deleted in both osteoblasts and osteoclasts) do not show a more severe phenotype. Altogether, these findings provide strong evidence that SIRT1 is a positive regulator of bone mass and a promising target for the development of novel therapeutics for osteoporosis.

A novel method for extracting nucleic acids from dried blood spots for ultrasensitive detection of low-density Plasmodium falciparum and Plasmodium vivax infections.

BACKGROUND: Greater Mekong Subregion countries are committed to eliminating Plasmodium falciparum malaria by 2025. Current elimination interventions target infections at parasite densities that can be detected by standard microscopy or rapid diagnostic tests (RDTs). More sensitive detection methods have been developed to detect lower density "asymptomatic" infections that may represent an important transmission reservoir. These ultrasensitive polymerase chain reaction (usPCR) tests have been used to identify target populations for mass drug administration (MDA). To date, malaria usPCR tests have used either venous or capillary blood sampling, which entails complex sample collection, processing and shipping requirements. An ultrasensitive method performed on standard dried blood spots (DBS) would greatly facilitate the molecular surveillance studies needed for targeting elimination interventions. METHODS: A highly sensitive method for detecting Plasmodium falciparum and P. vivax 18S ribosomal RNA from DBS was developed by empirically optimizing nucleic acid extraction conditions. The limit of detection (LoD) was determined using spiked DBS samples that were dried and stored under simulated field conditions. Further, to assess its utility for routine molecular surveillance, two cross-sectional surveys were performed in Myanmar during the wet and dry seasons. RESULTS: The lower LoD of the DBS-based ultrasensitive assay was 20 parasites/mL for DBS collected on Whatman 3MM filter paper and 23 parasites/mL for Whatman 903 Protein Saver cards-equivalent to 1 parasite per 50 µL DBS. This is about 5000-fold more sensitive than standard RDTs and similar to the LoD of ≤16-22 parasites/mL reported for other ultrasensitive methods based on whole blood. In two cross-sectional surveys in Myanmar, nearly identical prevalence estimates were obtained from contemporaneous DBS samples and capillary blood samples collected during the wet and dry season. CONCLUSIONS: The DBS-based ultrasensitive method described in this study shows equal sensitivity as previously described methods based on whole blood, both in its limit of detection and prevalence estimates in two field surveys. The reduced cost and complexity of this method will allow for the scale-up of surveillance studies to target MDA and other malaria elimination interventions, and help lead to a better understanding of the epidemiology of low-density malaria infections.

SIRT1 is a positive regulator of the master osteoblast transcription factor, RUNX2.

Activation of SIRT1 has previously been shown to protect mice against osteoporosis through yet ill-defined mechanisms. In this study, we outline a role for SIRT1 as a positive regulator of the master osteoblast transcription factor, RUNX2. We find that ex vivo deletion of sirt1 leads to decreased expression of runx2 downstream targets, but not runx2 itself, along with reduced osteoblast differentiation. Reciprocally, treatment with a SIRT1 agonist promotes osteoblast differentiation, as well as the expression of runx2 downstream targets, in a SIRT1-dependent manner. Biochemical and luciferase reporter assays demonstrate that SIRT1 interacts with and promotes the transactivation potential of RUNX2. Intriguingly, mice treated with the SIRT1 agonist, resveratrol, show similar increases in the expression of RUNX2 targets in their calvaria (bone tissue), validating SIRT1 as a physiologically relevant regulator of RUNX2.

Malaria Parasite CLAG3, a Protein Linked to Nutrient Channels, Participates in High Molecular Weight Membrane-Associated Complexes in the Infected Erythrocyte.

Malaria infected erythrocytes show increased permeability to a number of solutes important for parasite growth as mediated by the Plasmodial Surface Anion Channel (PSAC). The P. falciparum clag3 genes have recently been identified as key determinants of PSAC, though exactly how they contribute to channel function and whether additional host/parasite proteins are required remain unknown. To begin to answer these questions, I have taken a biochemical approach. Here I have used an epitope-tagged CLAG3 parasite to perform co-immunoprecipitation experiments using membrane fractions of infected erythrocytes. Native PAGE and mass spectrometry studies reveal that CLAG3 participate in at least three different high molecular weight complexes: a ~720kDa complex consisting of CLAG3, RHOPH2 and RHOPH3; a ~620kDa complex consisting of CLAG3 and RHOPH2; and a ~480kDa complex composed solely of CLAG3. Importantly, these complexes can be found throughout the parasite lifecycle but are absent in untransfected controls. Extracellular biotin labeling and protease susceptibility studies localize the 480kDa complex to the erythrocyte membrane. This complex, likely composed of a homo-oligomer of 160kDa CLAG3, may represent a functional subunit, possibly the pore, of PSAC.

One in four individuals of African-American ancestry harbors a 5.5kb deletion at chromosome 11q13.1.

Cloning and sequencing of 5.5 kb deletion at chromosome 11q13.1 from the HeLa cells, tumorigenic hybrids and two fibroblast cell lines have revealed homologous recombination between AluSx and AluY resulting in the deletion of intervening sequences. Long-range PCR of the 5.5 kb sequence in 494 normal lymphocyte samples showed heterozygous deletion in 28.3% of African-American ancestry samples but only in 4.8% of Caucasian samples (p<0.0001). This observation is strengthened by the copy number variation (CNV) data of the HapMap samples which showed that this deletion occurs in 27% of YRI (Yoruba--West African) population but none in non-African populations. The HapMap analysis further identified strong linkage disequilibrium between 5 single nucleotide polymorphisms and the 5.5 kb deletion in people of African ancestry. Computational analysis of 175 kb sequence surrounding the deletion site revealed enhanced flexibility, low thermodynamic stability, high repetitiveness, and stable stem-loop/hairpin secondary structures that are hallmarks of common fragile sites.

An epigenetic antimalarial resistance mechanism involving parasite genes linked to nutrient uptake.

Acquired antimalarial drug resistance produces treatment failures and has led to periods of global disease resurgence. In Plasmodium falciparum, resistance is known to arise through genome-level changes such as mutations and gene duplications. We now report an epigenetic resistance mechanism involving genes responsible for the plasmodial surface anion channel, a nutrient channel that also transports ions and antimalarial compounds at the host erythrocyte membrane. Two blasticidin S-resistant lines exhibited markedly reduced expression of clag genes linked to channel activity, but had no genome-level changes. Silencing aborted production of the channel protein and was directly responsible for reduced uptake. Silencing affected clag paralogs on two chromosomes and was mediated by specific histone modifications, allowing a rapidly reversible drug resistance phenotype advantageous to the parasite. These findings implicate a novel epigenetic resistance mechanism that involves reduced host cell uptake and is a worrisome liability for water-soluble antimalarial drugs.

SIRT1 regulates differentiation of mesenchymal stem cells by deacetylating ß-catenin.

Mesenchymal stem cells (MSCs) are multi-potent cells that can differentiate into osteoblasts, adipocytes, chondrocytes and myocytes. This potential declines with aging. We investigated whether the sirtuin SIRT1 had a function in MSCs by creating MSC specific SIRT1 knock-out (MSCKO) mice. Aged MSCKO mice (2.2 years old) showed defects in tissues derived from MSCs; i.e. a reduction in subcutaneous fat, cortical bone thickness and trabecular volume. Young mice showed related but less pronounced effects. MSCs isolated from MSCKO mice showed reduced differentiation towards osteoblasts and chondrocytes in vitro, but no difference in proliferation or apoptosis. Expression of ß-catenin targets important for differentiation was reduced in MSCKO cells. Moreover, while ß-catenin itself (T41A mutant resistant to cytosolic turnover) accumulated in the nuclei of wild-type MSCs, it was unable to do so in MSCKO cells. However, mutating K49R or K345R in ß-catenin to mimic deacetylation restored nuclear localization and differentiation potential in MSCKO cells. We conclude that SIRT1 deacetylates ß-catenin to promote its accumulation in the nucleus leading to transcription of genes for MSC differentiation.

Myeloid cell sirtuin-1 expression does not alter host immune responses to Gram-negative endotoxemia or Gram-positive bacterial infection.

The role of sirtuin-1 (SIRT1) in innate immunity, and in particular the influence of SIRT1 on antimicrobial defense against infection, has yet to be reported but is important to define since SIRT1 inhibitors are being investigated as therapeutic agents in the treatment of cancer, Huntington's disease, and autoimmune diseases. Given the therapeutic potential of SIRT1 suppression, we sought to characterize the role of SIRT1 in host defense. Utilizing both pharmacologic methods and a genetic knockout, we demonstrate that SIRT1 expression has little influence on macrophage and neutrophil antimicrobial functions. Myeloid SIRT1 expression does not change mortality in gram-negative toxin-induced shock or gram-positive bacteremia, suggesting that therapeutic suppression of SIRT1 may be done safely without suppression of myeloid cell-specific immune responses to severe bacterial infections.