Toll-like receptor 4 stimulation before or after Streptococcus pneumoniae induced sepsis improves survival and is dependent on T-cells

Introduction

Endotoxin tolerance improves outcomes from gram negative sepsis but the underlying mechanism is not known. We determined if endotoxin tolerance before or after pneumococcal sepsis improved survival and the role of lymphocytes in this protection.

Methods

Mice received lipopolysaccharide (LPS) or vehicle before or after a lethal dose of Streptococcus pneumoniae. Survival, quantitative bacteriology, liver function, and cytokine concentrations were measured. We confirmed the necessity of Toll-like receptor 4 (TLR4) for endotoxin tolerance using C3H/HeN (TLR4 replete) and C3H/HeJ (TLR4 deficient) mice. The role of complement was investigated through A/J mice deficient in C5 complement. CBA/CaHN-Btk^xid//J mice with dysfunctional B cells and Rag-1 knockout (KO) mice deficient in T and B cells delineated the role of lymphocytes.

Results

Endotoxin tolerance improved survival from pneumococcal sepsis in mice with TLR4 that received LPS pretreatment or posttreatment. Survival was associated with reduced bacterial burden and serum cytokine concentrations. Death was associated with abnormal liver function and blood glucose concentrations. Endotoxin tolerance improved survival in A/J and CBA/CaHN-Btk^xid//J mice but not Rag-1 KO mice.

Conclusions

TLR4 stimulation before or after S. pneumoniae infection improved survival and was dependent on T-cells but did not require an intact complement cascade or functional B cells.

Eukaryotic translation initiation factor 5A small interference RNA-liposome complexes reduce inflammation and increase survival in murine models of severe sepsis and acute lung injury

BACKGROUND

Many novel therapeutics have failed to reduce all-cause mortality associated with severe sepsis. Eukaryotic translation initiation factor 5A (eIF5A) is a regulator of apoptosis as well as inflammatory cell activation, making it a potential target for sepsis therapy.

METHODS

In a murine model of severe sepsis, mice were intraperitoneally challenged with lipopolysaccharide (LPS). Mice were treated both before and after LPS challenge with liposome complexes containing either an eIF5A-specific or control small interference RNA (siRNA), and both survival and serum concentrations of inflammatory cytokines were monitored. The ability of eIF5A siRNA to reduce inflammatory cytokines was also tested in a model of acute lung injury established by intranasal administration of LPS to mice.

RESULTS

There was a statistically significant increase in the rate of survival for mice intraperitoneally challenged with LPS that received eIF5A siRNA, compared with that noted for mice that received control siRNA (71% vs. 5%; P< .001), as well as a reduction in cytokine expression in serum. Concentrations of proinflammatory cytokines were also reduced in the lung homogenates and serum of mice that were intranasally challenged with LPS and received eIF5A siRNA (P< or = .05).

CONCLUSIONS

eIF5A siRNA-liposome complexes reduced inflammation and contributed to increased survival in a model of severe sepsis, decreased inflammation in a model of acute lung injury, and should be considered for clinical use.

An A2A adenosine receptor agonist, ATL313, reduces inflammation and improves survival in murine sepsis models

Background

The pathophysiology of sepsis is due in part to early systemic inflammation. Here we describe molecular and cellular responses, as well as survival, in A_2A adenosine receptor (AR) agonist treated and untreated animals during experimental sepsis.

Methods

Sepsis was induced in mice by intraperitoneal inoculation of live bacteria (Escherichia coli or Staphylococcus aureus) or lipopolysaccharide (LPS). Mice inoculated with live bacteria were treated with an A_2A AR agonist (ATL313) or phosphate buffered saline (PBS), with or without the addition of a dose of ceftriaxone. LPS inoculated mice were treated with ATL313 or PBS. Serum cytokines and chemokines were measured sequentially at 1, 2, 4, 8, and 24 hours after LPS was administered. In survival studies, mice were followed until death or for 7 days.

Results

There was a significant survival benefit in mice infected with live E. coli (100% vs. 20%, p = 0.013) or S. aureus (60% vs. 20%, p = 0.02) when treated with ATL313 in conjunction with an antibiotic versus antibiotic alone. ATL313 also improved survival from endotoxic shock when compared to PBS treatment (90% vs. 40%, p = 0.005). The serum concentrations of TNF-α, MIP-1α, MCP-1, IFN-γ, and IL-17 were decreased by ATL313 after LPS injection (p < 0.05). Additionally, ATL313 increased the concentration of IL-10 under the same conditions (p < 0.05). Circulating white blood cell concentrations were higher in ATL313 treated animals (p < 0.01).

Conclusion

Further studies are warranted to determine the clinical utility of ATL313 as a novel treatment for sepsis.

A new method for measuring blood-brain barrier permeability demonstrated with Europium-bound albumin during experimental lipopolysaccharide (LPS) induced meningitis in the rat

The blood-brain barrier (BBB) is a critical extrameningeal site of injury during bacterial meningitis, manifested by enhanced BBB permeability (BBBP). Previous methods to measure altered BBBP during meningitis involve radioactive materials, or are poorly quantified. Europium (EU) is a fluorescent, non-radioactive metal that is a sensitive and stable marker. Europium fluorescence can be measured with a spectrophotometer capable of time-resolved fluorescence (TRF). We used EU-albumin (EU-A) to examine BBBP in experimental lipopolysaccharide (LPS) induced meningitis. The results presented here introduce a simple and accurate method for measuring BBB permeability.

Targeting of Pseudomonas aeruginosa in the bloodstream with bispecific monoclonal antibodies

We examined the ability of a bispecific mAb reagent, consisting of a mAb specific for the primate erythrocyte complement receptor cross-linked with an anti-bacterial mAb, to target bacteria in the bloodstream in an acute infusion model in monkeys. In vitro studies demonstrated a variable level of complement-mediated binding (immune adherence) of Pseudomonas aeruginosa (strain PAO1) to primate E in serum. In vivo experiments in animals depleted of complement revealed that binding of bacteria to E was <1% before administration of the bispecific reagent, but within 5 min of its infusion, >99% of the bacteria bound to E. In complement-replete monkeys, a variable fraction of infused bacteria bound to E. This finding may have significant implications in the interpretation of animal models and in the understanding of bacteremias in humans. Treatment of these complement-replete monkeys with the bispecific reagent led to >99% binding of bacteria to E. Twenty-four-hour survival studies were conducted; several clinical parameters, including the degree of lung damage, cytokine levels, and liver enzymes in the circulation, indicate that the bispecific mAb reagent provides a degree of protection against the bacterial challenge.

A bispecific dsDNAxmonoclonal antibody construct for clearance of anti-dsDNA IgG in systemic lupus erythematosus

High avidity anti-dsDNA IgG antibodies are believed to play an important role in the pathogenesis of the autoimmune disease systemic lupus erythematosus (SLE) and therefore attempts have been made to reduce the concentration of these antibodies in the bloodstream of SLE patients. Previously we reported the development of an antigen based heteropolymer (AHP), a bispecific complex prepared by using the avidin-biotin system to crosslink dsDNA to a mAb specific for the human erythrocyte (E) complement receptor. Our studies indicated that this AHP could bind anti-dsDNA antibodies to E and facilitate clearance of these autoantibodies from the circulation of a monkey without E destruction. Here we report an improved covalent crosslinking procedure and purification scheme in which the AHP construct is isolated by precipitation in 50% saturated ammonium sulfate. We used a dsDNA binding dye, PicoGreen, to demonstrate specificity of binding of dsDNA to E via the AHP. The efficacy of the AHP in binding IgG anti-dsDNA antibodies to E was demonstrated in a sensitive and quantitative assay, based on the time resolved fluorescence properties of europium-labeled anti-human IgG mAbs used to probe the E. We also used this assay to screen SLE patient and normal plasmas for levels of anti-dsDNA IgG. The results of this assay correlate very well with the Farr assay, and therefore this approach may be useful in the development of informative and specific assays for a variety of autoantibodies. Treatment of SLE plasmas with E-AHP under conditions close to physiological led to substantial reductions (> or = 90%) in anti-dsDNA titers. It should be possible to test these new AHP for their ability to target and safely remove IgG anti-dsDNA antibodies from the circulation in animal models.

Bispecific monoclonal antibodies mediate binding of dengue virus to erythrocytes in a monkey model of passive viremia

Dengue viruses (DEN), causative agents of dengue fever (DF) and more severe dengue hemorrhagic fever (DHF)/dengue shock syndrome, infect over 100 million people every year. Among those infected, up to one-half million people develop DHF, which requires an extensive hospital stay. Recent reports indicate that there is a significant correlation between virus titer in the bloodstream of infected individuals and the severity of the disease, especially the development of DHF. This suggests that if there is a procedure to reduce viremia in infected subjects, then the severity of the disease may be controlled during the critical early stages of the disease before it progresses to DHF. We have generated bispecific mAb complexes (heteropolymer(s), HP), which contain a mAb specific for the DEN envelope glycoprotein cross-linked with a second mAb specific for the primate E complement receptor 1. These HP facilitate rapid binding of DEN to human and monkey E in vitro, with approximately 90% bound within 5 min. Furthermore, in a passive viremia monkey model established by continuous steady state infusion of DEN, injection of HP during the steady state promoted rapid binding of DEN to the E, followed by subsequent clearance from the vascular system. Moreover, HP previously infused into the circulation is capable of efficiently capturing a subsequent challenge dose of DEN and binding it to E. These data suggest that HP potentially can be useful for alleviating DEN infection-associated symptoms by reducing titers of free virus in the vascular system.

Infusion of bispecific monoclonal antibody complexes into monkeys provides immunologic protection against later challenge with a model pathogen

Heteropolymers (HP), bispecific mAbs which bind target pathogens to primate erythrocytes via complement receptor 1, facilitate clearance of pathogens from the bloodstream by targeting them for destruction in the liver without causing lysis or clearance of the erythrocytes. We show that when HP prepared with mouse IgG are intravenously infused into monkeys one or more times prior to exposure to a prototype pathogen, they bind to erythrocytes and remain in the circulation long enough to act as "sentinels," preventing pathogen invasion of the bloodstream. The effectiveness of HP as sentinels is limited both by the monkey's immune response to the HP and, prior to the immune response, by a gradual loss of the HP from monkey erythrocytes over a period of 1 week, and we have investigated possible causes of this HP loss. In overview, our results suggest that HP prepared with mouse IgG are able to effectively function as sentinels for a minimum of 4 days and, after repeat infusion, possibly for up to 2 weeks.

Bispecific monoclonal antibody complexes facilitate erythrocyte binding and liver clearance of a prototype particulate pathogen in a monkey model

We used Anger camera imaging in a monkey model to investigate the organ localization of a prototype particulate pathogen, 131I-labeled bacteriophage phi X174, after it was bound to the primate erythrocyte complement receptor and then cleared from the circulation. This 131I-labeled phi X174 was infused into the circulation of an immunized monkey, and the nascently formed immune complexes showed rapid and quantitative binding to erythrocytes via the immune adherence reaction (complement-mediated binding). Alternatively, phi X174 was infused into the circulation of a naive animal, and then cross-linked bispecific mAb complexes (heteropolymers, anti-CR1 x anti-phi X174) were infused into the circulation. The infused heteropolymers also facilitated rapid and quantitative binding of phi X174 to erythrocytes. In both cases, after a short lag period, the erythrocyte-bound phi X174 was rapidly cleared from the circulation, and the vast majority of the radiolabel was cleared to the liver, with a small amount clearing to the spleen. Further liver imaging confirmed that within 24 h most of the bacteriophage previously cleared to the liver via the heteropolymer system was phagocytosed and destroyed. The findings in this model system provide additional evidence for the potential utility of heteropolymers to facilitate the safe and rapid clearance of blood-borne pathogens as a potential treatment for infectious diseases.

Bispecific monoclonal antibody complexes facilitate erythrocyte binding and liver clearance of a prototype particulate pathogen in a monkey model

We used Anger camera imaging in a monkey model to investigate the organ localization of a prototype particulate pathogen, 131I-labeled bacteriophage phi X174, after it was bound to the primate erythrocyte complement receptor and then cleared from the circulation. This 131I-labeled phi X174 was infused into the circulation of an immunized monkey, and the nascently formed immune complexes showed rapid and quantitative binding to erythrocytes via the immune adherence reaction (complement-mediated binding). Alternatively, phi X174 was infused into the circulation of a naive animal, and then cross-linked bispecific mAb complexes (heteropolymers, anti-CR1 x anti-phi X174) were infused into the circulation. The infused heteropolymers also facilitated rapid and quantitative binding of phi X174 to erythrocytes. In both cases, after a short lag period, the erythrocyte-bound phi X174 was rapidly cleared from the circulation, and the vast majority of the radiolabel was cleared to the liver, with a small amount clearing to the spleen. Further liver imaging confirmed that within 24 h most of the bacteriophage previously cleared to the liver via the heteropolymer system was phagocytosed and destroyed. The findings in this model system provide additional evidence for the potential utility of heteropolymers to facilitate the safe and rapid clearance of blood-borne pathogens as a potential treatment for infectious diseases.

The primate erythrocyte complement receptor (CR1) as a privileged site: binding of immunoglobulin G to erythrocyte CR1 does not target erythrocytes for phagocytosis

The primate erythrocyte (E) complement receptor, CR1, is a transmembrane glycoprotein located in clusters on the surface of E. In vivo studies have demonstrated that during processing and clearance of complement-opsonized immune complexes, large amounts of immunoglobulin G (IgG) can be bound to primate E via CR1 with no E loss or lysis. However, when comparable amounts of IgG are bound to other sites on E, in many cases the E are cleared from the circulation by the mononuclear phagocytic system. Therefore, due to its role in immune complex processing, CR1 may represent a privileged site on the primate E. To delineate further this property of E CR1, we performed in vitro phagocytosis assays in the absence of complement and examined the ingestion of E, opsonized at various sites with IgG, by peripheral blood monocytes. When either human or rhesus monkey E were opsonized at sites other than CR1, with between 1,000 and 15,000 IgG per E, substantial phagocytosis of E was evident. However, when comparable amounts of IgG were bound exclusively via CR1, little, if any, phagocytosis was observed. The key to the low phagocytic level of E opsonized via CR1 may be related to the requirements of a "zipper mechanism" for phagocytosis first annunciated by Griffin et al. Based on their findings, we suggest that due to the presence of preexisting clusters of CR1 on the E membrane, large amounts of IgG can be bound to E under conditions that preclude circumferential engagement (and phagocytosis) of the entire E by Fc receptors on the monocyte.

Bispecific monoclonal antibody complexes bound to primate erythrocyte complement receptor 1 facilitate virus clearance in a monkey model

We investigated the feasibility of using bispecific mAb complexes to redirect and improve the efficiency of the primate E complement receptor 1-based clearance reaction to remove a virus from the circulation. As an initial approach, we used bacteriophage phiX174 as an immunologic model for mammalian viruses. Bispecific complexes were prepared by chemically cross-linking a mAb specific for complement receptor 1 with a mAb specific for the bacteriophage phiX174. In a monkey model these complexes facilitate rapid and quantitative binding of the target bacteriophage to E in vitro and in vivo. Moreover, after in vivo binding to E, the complexes containing mAb and prototype virus are rapidly cleared from the circulation of rhesus and cynomolgus monkeys without loss of E. Our findings suggest that bispecific mAb complexes, in concert with primate E complement receptor 1, may have therapeutic utility in the treatment of diseases associated with blood-borne pathogens.

Bispecific monoclonal antibody complexes bound to primate erythrocyte complement receptor 1 facilitate virus clearance in a monkey model

We investigated the feasibility of using bispecific mAb complexes to redirect and improve the efficiency of the primate E complement receptor 1-based clearance reaction to remove a virus from the circulation. As an initial approach, we used bacteriophage phiX174 as an immunologic model for mammalian viruses. Bispecific complexes were prepared by chemically cross-linking a mAb specific for complement receptor 1 with a mAb specific for the bacteriophage phiX174. In a monkey model these complexes facilitate rapid and quantitative binding of the target bacteriophage to E in vitro and in vivo. Moreover, after in vivo binding to E, the complexes containing mAb and prototype virus are rapidly cleared from the circulation of rhesus and cynomolgus monkeys without loss of E. Our findings suggest that bispecific mAb complexes, in concert with primate E complement receptor 1, may have therapeutic utility in the treatment of diseases associated with blood-borne pathogens.

Immune complexes bound to the primate erythrocyte complement receptor (CR1) via anti-CR1 mAbs are cleared simultaneously with loss of CR1 in a concerted reaction in a rhesus monkey model

In the circulation of primates, C3b-opsonized immune complexes (IC) bound to erythrocyte (E) CR1 are taken to the liver and spleen where IC are removed and destroyed without lysis or sequestration of E. Individuals with diseases associated with IC processing often have decreased E CR1 levels, and in previous primate animal models of IC disease, E CR1 was shown to be reduced, but the relationship between IC processing and CR1 loss remained to be clarified. We have developed a simple model to study this question. In naive (nonimmunized) rhesus monkeys, E-bound mouse anti-CR1 mAbs (1500 IgG/E) are not rapidly cleared from the circulation. Infusion of monkey anti-mouse IgG leads to rapid indirect binding of this second antibody to E CR1. Subsequently, in what appears to be a concerted reaction, CR1-bound nascent IC are rapidly cleared from the circulation and CR1 is removed from E at the same rate. Clearance of bound IC and loss of CR1 were both independently followed by RIA. Imaging studies localized the cleared anti-CR1 mAbs to the liver. Western blots indicated that the loss of CR1 was not due to a conformational change, and E CR1 levels returned to normal in 2-3 weeks, suggesting that the return was associated with synthesis of new E. Our findings suggest that the key step in the clearance mechanism requires recognition (possibly by Fc receptors) of IC-like material associated with E CR1, and this leads to loss of CR1 and uptake of the CR1-IC substrate by liver phagocytic cells.

Antigen-based heteropolymers facilitate, via primate erythrocyte complement receptor type 1, rapid erythrocyte binding of an autoantibody and its clearance from the circulation in rhesus monkeys

We investigated the feasibility of using the primate E complement receptor (CR1), in concert with Ag-based heteropolymers (AHP), as a potential therapy to remove autoantibodies from the circulation. AHP are prepared by cross-linking an anti-CR1 mAb with the acetylcholine receptor (AChR), the principal target Ag in myasthenia gravis. In vitro studies demonstrate that this methodology facilitates specific, rapid, and quantitative binding of an anti-AChR mAb to primate Es. In vivo experiments in rhesus monkeys indicate that AHP-mediated binding of an anti-AChR mAb to Es leads to the clearance of the mAb from the circulation. Once bound to the E via the AHP, the autoantibody is transported to the liver and spleen, where it is degraded without destruction of the E. It is therefore likely that the complexes of AHP and target mAb, when bound to Es, are recognized in vivo and processed by a mechanism quite similar to that which occurs when complement-opsonized immune complexes, bound to primate Es, are cleared from the circulation. It may be possible to extend and generalize this work to allow for the development of a simple, noninvasive therapy that can be made specific for the treatment of several different autoimmune diseases.

Antigen-based heteropolymers facilitate, via primate erythrocyte complement receptor type 1, rapid erythrocyte binding of an autoantibody and its clearance from the circulation in rhesus monkeys

We investigated the feasibility of using the primate E complement receptor (CR1), in concert with Ag-based heteropolymers (AHP), as a potential therapy to remove autoantibodies from the circulation. AHP are prepared by cross-linking an anti-CR1 mAb with the acetylcholine receptor (AChR), the principal target Ag in myasthenia gravis. In vitro studies demonstrate that this methodology facilitates specific, rapid, and quantitative binding of an anti-AChR mAb to primate Es. In vivo experiments in rhesus monkeys indicate that AHP-mediated binding of an anti-AChR mAb to Es leads to the clearance of the mAb from the circulation. Once bound to the E via the AHP, the autoantibody is transported to the liver and spleen, where it is degraded without destruction of the E. It is therefore likely that the complexes of AHP and target mAb, when bound to Es, are recognized in vivo and processed by a mechanism quite similar to that which occurs when complement-opsonized immune complexes, bound to primate Es, are cleared from the circulation. It may be possible to extend and generalize this work to allow for the development of a simple, noninvasive therapy that can be made specific for the treatment of several different autoimmune diseases.

Antigen-based heteropolymers. A potential therapy for binding and clearing autoantibodies via erythrocyte CR1

OBJECTIVE

To determine if complexes containing monoclonal antibodies to CR1 cross-linked with antigen (antigen-based heteropolymers [AHP]) can bind the corresponding autoantibody to primate erythrocyte CR1 and promote autoantibody clearance from the circulation.

METHODS

AHP were constructed by cross-linking double-stranded DNA (dsDNA) to monoclonal antibodies to CR1. The ability of AHP to facilitate binding of human anti-dsDNA antibodies to primate erythrocytes was studied in vitro using a variety of radioimmunoassays (including Farr assays), enzyme immunoassays, and fluorescence-activated cell sorting. In addition, we used a monkey model to study in vivo the AHP-mediated clearance of passively infused human anti-dsDNA antibodies.

RESULTS

Large amounts of lupus IgG anti-dsDNA antibodies can be specifically bound to human erythrocytes via the complexes, and studies in 2 rhesus monkeys indicate that the erythrocyte-bound antibodies are rapidly cleared from the circulation.

CONCLUSION

This methodology may allow for development of a new therapy to facilitate autoantibody clearance in autoimmune disease.

Cross-linked bispecific monoclonal antibody heteropolymers facilitate the clearance of human IgM from the circulation of squirrel monkeys

We have previously demonstrated that cross-linked bispecific monoclonal antibodies (mAb) heteropolymers (HP), specific for primate erythrocyte (E) complement receptor type 1 (CR1) and target antigen (Ag), facilitate the binding of these target Ag to human and non-human primate E. Once bound in vitro to rhesus monkey E, upon re-infusion these HP/Ag complexes are recognized in vivo by cells of the reticuloendothelial system (RES) and removed from the circulation without loss of the E. We now show, in squirrel monkeys, that an HP specific for E CR1 and human IgM (anti-CR1 x anti-IgM) can be used to facilitate in vivo E binding and clearance from the circulation of a previously injected and circulating model protein pathogen, human IgM. Approximately 70-80% of 125I-labeled human IgM is cleared from the circulation of each of five squirrel monkeys via the HP system. We observe, in experiments analogous to previous studies on immune complex (IC) clearance, that subsequent to HP/Ag clearance there is a decrease in the number of CR1 epitopes per E which is manifested when we use both monoclonal and polyclonal anti-CR1 probes. Our results indicate that the primary organs responsible for uptake of the complexes are the liver and spleen. This work strongly suggests that the HP/Ag complexes, bound to E, function as IC prototypes and are recognized and processed as such in vivo. Thus, the HP-E system may eventually serve as a viable immunotherapy for the clearance of blood-borne pathogens from the circulation.