Andrzej Tarkowski

Vaccination with a recombinant fragment of collagen adhesin provides protection against Staphylococcus aureus-mediated septic death.

Staphylococcus aureus is a major cause of nosocomial and community-acquired infections. Morbidity and mortality due to infections such as sepsis, osteomyelitis, septic arthritis, and invasive endocarditis remain high despite the use of antibiotics. The emergence of antibiotic resistant super bugs mandates that alternative strategies for the prevention and treatment of S. aureus infections are developed. We investigated the ability of vaccination with a recombinant fragment of the S. aureus collagen adhesin to protect mice against sepsis-induced death. Actively immunized NMRI mice were intravenously inoculated with the S. aureus clinical isolate strain Phillips. 14 d after inoculation, mortality in the collagen adhesin-vaccinated group was only 13%, compared with 87% in the control antigen immunized group (P < 0.001). To determine if the protective effect was antibody mediated, we passively immunized naive mice with collagen adhesin-specific antibodies. Similar to the active immunization strategy, passive transfer of collagen adhesin-specific antibodies protected mice against sepsis-induced death. In vitro experiments indicated that S. aureus opsonized with sera from collagen adhesin immunized mice promoted phagocytic uptake and enhanced intracellular killing compared with bacteria opsonized with sera from control animals. These results indicate that the collagen adhesin is a viable target in the development of immunotherapeutics against S. aureus.

Estrogen accelerates immune complex glomerulonephritis but ameliorates T cell-mediated vasculitis and sialadenitis in autoimmune MRL lpr/lpr mice

Estrogen is known to influence immune responses in healthy subjects in a dichotomous fashion. Thus, in number of previous studies we and others have demonstrated that B cell activities are augmented after exposure to estrogen whereas T cell reactivity is suppressed. Furthermore, it has been shown that this hormone has significant impact on the course of certain human and experimental autoimmune diseases. In this study we report that treatment with physiological doses of estradiol exerts dichotomous effects on different manifestations of the lupus disease in MRL/l mice. On one hand immune complex-mediated glomerulonephritis was significantly accelerated. This outcome was due to polyclonal B cell activation with increased production of antibodies to double-stranded DNA and formation of circulating immune complexes. In contrast, T cell-mediated lesions such as focal sialadenitis, renal vasculitis, and periarticular inflammation were all significantly ameliorated in MRL/l mice exposed to estrogen. Thus, we were able to demonstrate that, within one subject and even within one organ, administration of estrogen leads to differential outcome of SLE morbidity. We propose that the differential effect of estrogen on the manifestations of the autoimmune disease of MRL/l mice is due to its dichotomous effects on B and T cell-mediated immune responses.

Anti-inflammatory properties of estrogen: I. In vivo suppression of leukocyte production in bone marrow and redistribution of peripheral blood neutrophils

We have recently demonstrated that estrogen has differential immunomodulatory properties in mice because it stimulates antibody responses but inhibits T cell-mediated inflammation. In the present study we have examined the influence of estrogen on T cell-independent inflammatory responses. A local inflammation was induced by intradermal injection of olive oil and cholera toxin. Treatment of castrated mice with pharmacological and even physiological doses of estradiol significantly suppressed the inflammatory response, as measured by footpad swelling and documented by histologic examination. Even a single injection of a low dose of estradiol (3.2 micrograms/mouse) given up to 4 days prior to the administration of the phlogistic compound reduced the inflammatory response. Our results demonstrate that the mechanisms whereby estrogen exerts its anti-inflammatory property are probably not mediated by modulation of corticosteroid production. Instead, it is evidenced that estrogen significantly suppresses the bone marrow production of leukocytes and affects the distribution of polymorphonuclear cells in peripheral blood. The possible implications of our results are discussed in the context of the modulation of inflammatory rheumatic diseases.

Role of Neutrophil Leukocytes in Cutaneous Infection Caused by Staphylococcus aureus

ABSTRACT Despite the high prevalence of cutaneous infections, little is known about the role of host immune responsiveness duringStaphylococcus aureus dermatitis. We have recently described a murine model of infectious dermatitis induced by superantigen-producing S. aureus. To assess the role of neutrophils in staphylococcal dermatitis, mice were given granulocyte-depleting monoclonal antibody prior to and on several occasions following intracutaneous inoculation with staphylococci. The granulocyte-depleted mice that had been intradermally inoculated withS. aureus developed crusted ulcerations which tended not to heal, whereas animals injected with control monoclonal antibody displayed only minor and transient skin lesions. The finding of severe ulcerations in neutropenic mice correlated with a significantly higher burden of bacteria in the blood and skin during the early phase of the infection. Importantly, while mice with an intact granulocyte population showed only limited skin infection, bacteremia occurred in the great majority of the neutrophil-depleted animals. As a consequence, the latter individuals exhibited significantly increased levels of the proinflammatory cytokine interleukin-6 and specific antibodies to staphylococcal cell wall components and toxic shock syndrome toxin-1 in the serum. Our data point to a crucial protective role of granulocytes in S. aureus dermatitis.

The role of Staphylococcus aureus sortase A and sortase B in murine arthritis

Gram-positive pathogenic bacteria display proteins on their surface that play important roles during infection. In Staphylococcus aureus, these surface proteins are anchored to the cell wall by two sortase enzymes, SrtA and SrtB, that recognize specific surface protein sorting signals. The role of sortase enzymes in bacterial virulence was examined using a murine septic arthritis model. Intravenous inoculation with any of the Delta(srtA), Delta(srtB) or Delta(srtAB) mutants resulted in significantly increased survival and significantly lower weight loss compared with the parental strain. Mice inoculated with the Delta(srtA) mutant did not express severe arthritis, while arthritis in mice inoculated with the Delta(srtB) mutant was not different from that seen in mice that were infected with the wild-type parent strain. Furthermore, persistence of staphylococci in kidneys and joints following intravenous inoculation of mice was more pronounced for wild-type and Delta(srtB) mutant strains than for Delta(srtA) or Delta(srtAB) variants. Together these results indicate that sortase B (srtB) plays a contributing role during the pathogenesis of staphylococcal infections, whereas sortase A (srtA) is an essential virulence factor for the establishment of septic arthritis.

On the Role of Staphylococcus aureus Sortase and Sortase-Catalyzed Surface Protein Anchoring in Murine Septic Arthritis

Anchoring of Staphylococcus aureus surface protein to the cell wall is catalyzed by sortase, a transpeptidase. The contribution of staphylococcal surface proteins to establishment of infection was examined using a murine septic arthritis model. Intravenous inoculation of mice with the sortase-deficient mutant S. aureus strain SMK3 did not result in weight loss or severe septic arthritis, in contrast to the parent strain, S. aureus Newman. Direct inoculation of the sortase mutant into joint cavities also failed to cause severe synovitis or erosive arthritis. Furthermore, intravenous inoculation with staphylococci resulted in the rapid clearing of the sortase mutant from the bloodstream. This phenomenon demonstrates the involvement of host neutrophils; when these cells were depleted, sortase mutant staphylococci caused severe systemic infection, although not septic arthritis. These results suggest that sortase mutant staphylococci are significantly less virulent than the parent strain, Newman: the sortase mutant has decreased ability to reach target organs and, once there, to induce an inflammatory response.

Protection against Staphylococcus auveus Sepsis by Vaccination with Recombinant Staphylococcal Enterotoxin A Devoid of Superantigenicity

Staphylococcal exotoxins are virulence determinants in Staphylococcus aureus arthritis and septicemia. To assess the utility of enterotoxins as vaccine candidates for these diseases, a genetically modified staphylococcal enterotoxin A (SEA) that lacks superantigenic properties was used. Mice immunized with recombinant (r) SEA had significantly longer survival than control immunized mice and lost significantly less weight than the controls. Transfer of SEA-specific antibodies to naive mice resulted in good protection against death in staphylococcal sepsis. In vitro proliferative responses to SEA by naive lymphocytes were almost totally abolished on incubation with serum from rSEA but not with control antigen-immunized mice. These results suggest that immunization with rSEA devoid of superantigenic properties provides good protection against S. aureus sepsis. In addition, the data indicate that the protection is at least in part mediated by SEA neutralizing antibodies.

Sigma Factor B and RsbU Are Required for Virulence in Staphylococcus aureus-Induced Arthritis and Sepsis

ABSTRACT The prototype Staphylococcus aureus strain 8325-4 produces high levels of hemolysins and proteases. Recently it has been shown that this property depends on a deficiency of sigma factor B (SigB) activity controlling the activation of regulatory genes such as agr and sarA. SigB deficiency is in turn due to a mutation in the rsbU gene, which is required for posttranslational activation of SigB. The rsbU defect of strain 8325-4 has recently been repaired, and we used this strain (SH1000), along with its isogenic sigB-negative mutant, to investigate the contributions of RsbU and SigB in a murine model of septic arthritis. Intravenous inoculation with the rsbU-repaired isogenic strain SH1000 resulted in significantly more severe arthritis, weight decrease, and mortality compared to those of the parental strain 8325-4 (rsbU-negative) or the isogenic sigB-negative mutant (MJH502). SH1000 also persisted more in kidneys and joints of infected mice. Our data strongly suggest that RsbU and SigB regulate important virulence factors, thereby contributing significantly to the outcome of staphylococcal infection.

Virulence of a hemB mutant displaying the phenotype of a Staphylococcus aureus small colony variant in a murine model of septic arthritis

Persistence of Staphylococcus aureus during invasive infections has been associated with a small-colony variant (SCV) phenotype. SCVs are frequently auxotrophic for menadione or hemin, two compounds involved in the biosynthesis of the electron transport chain. SCVs have been shown to be more resistant to antibiotics such as aminoglycosides, grow slowly and persist intracellularly. The aim of this study was to assess the virulence of an hemB mutant, which has been shown to display the typical characteristics of clinical SCVs, in a murine model of septic arthritis. NMRI mice were inoculated intravenously with either the wild type strain Newman or with its mutant displaying the SCV phenotype. The clinical, bacteriological, and histopathological progression of the disease was studied. Mice inoculated with the hemB mutant displayed a higher frequency and a significantly higher severity of arthritis than mice inoculated with the wild type Newman strain. Despite that, the mutant inoculated mice displayed significantly lower bacterial burden in their kidneys and joints compared with mice exposed to the wild parental strain. Notably, the hemB mutant produced almost 20 times more protease in vitro than the parental strain. We conclude that the small colony variants of S. aureus are more virulent on a per organism basis than its isogenic parental strain in the model of septic arthritis. This can at least in part be explained by the ability of SCV to produce high amounts of destructive proteases.

Fibronectin-Binding Proteins and Fibrinogen-Binding Clumping Factors Play Distinct Roles in Staphylococcal Arthritis and Systemic Inflammation

Staphylococcus aureus is a commonly encountered pathogen in humans, and it has the potential to cause destructive and life-threatening conditions, including septic arthritis. The pathogenicity of staphylococci depends on the expression of virulence factors. Among these, staphylococcal cell-surface proteins with tissue-adhesive functions have been suggested to mediate the colonization of host tissues, a crucial step in the establishment of infection. We investigated the relative contribution of the fibronectin-binding proteins (FnBPs) and fibrinogen-binding clumping factors (Clfs) to staphylococcal virulence in an experimental model of septic arthritis. The results show that these 2 sets of proteins play distinctly different roles in the development and progression of septic arthritis. Although Clfs significantly contributed to the arthritogenicity of S. aureus, FnBPs had no effect on the development of arthritis. Conversely, FnBPs played an important role in the induction of systemic inflammation, characterized by interleukin-6 secretion, severe weight loss, and mortality.