Combined immunosuppressive and antibiotic therapy improves bacterial clearance and survival of polymicrobial septic peritonitis

Low-dose mycophenolate mofetil improves survival in a murine model of Staphylococcus aureus sepsis by increasing bacterial clearance and phagocyte function

Regulators of TLRs signaling pathways play an important role in the control of the pro-inflammatory response that contributes to sepsis-induced tissue injury. Mycophenolate mofetil, an immunosuppressive drug inhibiting lymphocyte proliferation, has been reported to be a regulator of TLRs signaling pathways. Whether MMF used at infra-immunosuppressive doses has an impact on survival and on innate immune response in sepsis is unknown.

C57BL/6J mice were infected intraperitoneally with 108 CFU Staphylococcus aureus, and treated or not with low-dose of MMF (20mg/kg/day during 4 days). Survival rate and bacterial clearance were compared. Cytokine levels, quantitative and qualitative cellular responses were assessed. S. aureus – infected mice treated with MMF exhibited improved survival compared to non-treated ones (48% vs 10%, p<0.001). With the dose used for all experiments, MMF did not show any effect on lymphocyte proliferation. MMF treatment also improved local and systemic bacterial clearance, improved phagocytosis activity of peritoneal macrophages resulting in decreased inflammatory cytokines secretion. MMF-treated mice showed enhanced activation of NF-κB seemed with a suspected TLR4-dependent mechanism. These results suggest that infra-immunosuppressive doses of MMF improve host defense during S. aureus sepsis and protects infected mice from fatal outcome by regulating innate immune responses. The signaling pathways involved could be TLR4-dependent. This work brings new perspectives in pathogenesis and therapeutic approaches of severe infections.

Pulmonary non-tuberculous mycobacterial infections: current state and future management

Currently, there is a trend of increasing incidence in pulmonary non-tuberculous mycobacterial infections (PNTM) together with a decrease in tuberculosis (TB) incidence, particularly in developed countries. The prevalence of PNTM in underdeveloped and developing countries remains unclear as there is still a lack of detection methods that could clearly diagnose PNTM applicable in these low-resource settings. Since non-tuberculous mycobacteria (NTM) are environmental pathogens, the vicinity favouring host-pathogen interactions is known as important predisposing factor for PNTM. The ongoing changes in world population, as well as socio-political and economic factors, are linked to the rise in the incidence of PNTM. Development is an important factor for the improvement of population well-being, but it has also been linked, in general, to detrimental environmental consequences, including the rise of emergent (usually neglected) infectious diseases, such as PNTM. The rise of neglected PNTM infections requires the expansion of the current efforts on the development of diagnostics, therapies and vaccines for mycobacterial diseases, which at present, are mainly focused on TB. This review discuss the current situation of PNTM and its predisposing factors, as well as the efforts and challenges for their control.

Mycophenolate Mofetil Protects Septic Mice via the Dual Inhibition of Inflammatory Cytokines and PD-1

Due to the imbalance between hyper-inflammation and hypo-inflammation, which are characterized by excessive cytokine productions and programmed death 1 (PD-1) upregulation, respectively, sepsis remains a highly lethal inflammatory syndrome with limited effective therapies. Mycophenolate mofetil (MMF), an immunosuppressant, has been reported to attenuate various inflammatory diseases. However, the role of MMF in sepsis therapy remains to be elucidated. C57BL-6J mice underwent cecal ligation and puncture (CLP) and were treated either with or without MMF. Survival rate and organ injuries were compared. Cytokine levels, bacteria clearance, apoptosis of spleen and peritoneal macrophages, and PD-1 expression were assessed. At the beginning of CLP, 60 mg/kg MMF administered by gavage significantly protected septic mice, which was evidenced by improved survival and attenuated organ injuries, decreased cytokines, lower bacterial loads, and alleviated immune cell apoptosis. In addition, immune cells in the MMF mice showed lower PD-1 expression and improved immune response to pathogeny stimuli. MMF protects septic mice via the dual inhibition of cytokine releasing and PD-1 expression.

Combined Human Genome-wide RNAi and Metabolite Analyses Identify IMPDH as a Host-Directed Target against Chlamydia Infection

Chlamydia trachomatis (Ctr) accounts for >130 million human infections annually. Since chronic Ctr infections are extremely difficult to treat, there is an urgent need for more effective therapeutics. As an obligate intracellular bacterium, Ctr strictly depends on the functional contribution of the host cell. Here, we combined a human genome-wide RNA interference screen with metabolic profiling to obtain detailed understanding of changes in the infected cell and identify druggable pathways essential for Ctr growth. We demonstrate that Ctr shifts the host metabolism toward aerobic glycolysis, consistent with increased biomass requirement. We identify key regulator complexes of glucose and nucleotide metabolism that govern Ctr infection processes. Pharmacological targeting of inosine-5'-monophosphate dehydrogenase (IMPDH), the rate-limiting enzyme in guanine nucleotide biosynthesis, efficiently inhibits Ctr growth both in vitro and in vivo. These results highlight the potency of genome-scale functional screening for the discovery of drug targets against bacterial infections.

FTY720-Induced Lymphopenia Does Not Aggravate Mortality in a Murine Model of Polymicrobial Abdominal Sepsis

BACKGROUND

FTY720 is an immunosuppressive molecule licensed for the treatment of chronic relapsing multiple sclerosis (MS). It attenuates the adaptive immune response by sequestering T cells within secondary lymphoid organs via its action as functional antagonist of sphingosine-1-phasphate. To date, it is unknown whether FTY-induced lymphopenia puts MS patients at increased risk for severe forms of postoperative infectious complications such as abdominal sepsis.

OBJECTIVES

To determine the effect of FTY720-induced lymphopenia on survival to sepsis secondary to postoperative intraabdominal infections in a murine model of polymicrobial sepsis.

METHODS

Detailed analysis of cellular dynamics in secondary lymphoid organs and of cytokine profiles was performed in FTY720-treated or placebo-treated C57BL/6 mice after induction of colon ascendens stent peritonitis (CASP). Furthermore, survival analysis was performed in FTY720-treated and placebo-treated animals in severe CASP. Fifty percent of each group were treated with broad spectrum antibiotics.

RESULTS

FTY720 treatment resulted in remodeling of cell populations present in the peripheral blood, the peritoneal cavity, and the spleen after CASP induction. Both lymphoid and myeloid cell lines were affected. However, survival in lymphopenic FTY720-treated animals was similar to placebo-treated mice following CASP. Antibiotic treatment increases survival in untreated as well as FTY720-treated animals to a similar extent.

DISCUSSION

Our data demonstrate that inhibition of T-cell migration and induction of peripheral lymphopenia did not affect survival in a model of severe murine sepsis. The presence of reduced T- and B-cell numbers in the peripheral blood during a septic challenge did not negatively affect sepsis mortality in our model of severe abdominal sepsis. The absence of increased mortality under FTY720 treatment in the CASP model suggests that FTY720 treatment will probably not result in increased mortality in MS patients suffering from sepsis.

The normalcy of dormancy: common themes in microbial quiescence

All microorganisms are exposed to periodic stresses that inhibit growth. Many bacteria and fungi weather these periods by entering a hardy, nonreplicating state, often termed quiescence or dormancy. When this occurs during an infection, the resulting slowly growing pathogen is able to tolerate both immune insults and prolonged antibiotic exposure. While the stresses encountered in a free-living environment may differ from those imposed by host immunity, these growth-limiting conditions impose common pressures, and many of the corresponding microbial responses appear to be universal. In this review, we discuss the common features of these growth-limited states, which suggest new approaches for treating chronic infections such as tuberculosis.

Beneficial effects of stress-dose corticosteroid therapy in canines depend on the severity of staphylococcal pneumonia

PURPOSE

The effects of stress-dose corticosteroid therapy were studied in a canine staphylococcal pneumonia model of septic shock.

METHODS

Immediately following intrabronchial bacterial challenge, purpose-bred beagles were treated with stress doses of desoxycorticosterone (DOC), a mineralocorticoid agonist, and dexamethasone (DEX), a glucocorticoid agonist, or with placebo for 96 h. Oxacillin (30 mg/kg every 8 h) was started 4 h after infection onset. Bacterial dose was titrated to achieve 80-90 % lethality (n = 20) using an adaptive design; additional animals (n = 18) were investigated using the highest bacterial dose.

RESULTS

Initial analysis of all animals (n = 38) demonstrated that the effects of DOC + DEX were significantly altered by bacterial dose (p = 0.04). The treatment effects of DOC + DEX were different in animals administered high or relatively lower bacterial doses in terms of survival (p = 0.05), shock reversal (p = 0.02), interleukin-6 levels (p = 0.02), and temperature (p = 0.01). DOC + DEX significantly improved the above parameters (p ≤ 0.03 for all) and lung injury scores (p = 0.02) after high-dose bacterial challenges, but not after lower challenges (p = not significant for all). Oxacillin trough levels were below the minimum inhibitory concentration of the infecting organism, and DOC + DEX increased the frequency of persistent staphylococcal bacteremia (odds ratio 3.09; 95 % confidence interval 1.05-9.11; p = 0.04).

CONCLUSIONS

Stress-dose corticosteroids were only beneficial in cases of sepsis with high risk for death and even short courses may interfere with host mechanisms of bacterial clearance.