Teresa Krakauer

The flavonoid baicalin inhibits superantigen-induced inflammatory cytokines and chemokines

Excessive release of proinflammatory cytokines mediates the toxic effect of superantigenic staphylococcal exotoxins (SE). Baicalin, a flavone isolated from the Chinese herb Scutellaria baicalensis Georgi and used in China to treat infectious diseases, inhibited SE‐stimulated T‐cell proliferation (by 98%) and production of interleukin 1β, interleukin 6, tumor necrosis factor, interferon γ, monocyte chemotactic protein 1, macrophage inflammatory protein (MIP)‐1α, and MIP‐1β mRNA and protein by human peripheral blood mononuclear cells. These data suggest that baicalin may be therapeutically useful for mitigating the pathogenic effects of SE by inhibiting the signaling pathways activated by superantigens.

Doxycycline Is Anti-Inflammatory and Inhibits Staphylococcal Exotoxin-Induced Cytokines and Chemokines

ABSTRACT Proinflammatory cytokines mediate the toxic effect of superantigenic staphylococcal exotoxins (SE). Doxycycline inhibited SE-stimulated T-cell proliferation and production of cytokines and chemokines by human peripheral blood mononuclear cells. These results suggest that the antibiotic doxycycline has anti-inflammatory effects and is therapeutically useful for mitigating the pathogenic effects of SE.

IL-10 inhibits the adhesion of leukocytic cells to IL-1-activated human endothelial cells

Cytokines play an important role in the recruitment of leukocytes from blood to sites of tissue injury and inflammation. Previous studies showed that the pro-inflammatory cytokine, IL-1, induces the adhesion of leukocytes by up-regulating the expression of the adhesion molecules ICAM-1 and VCAM-1 on endothelial cells. IL-10, a pleiotropic mediator, inhibits the production of cytokines by macrophages and down-regulates the antigen-presenting function of macrophages, thereby acting as a suppressor of immune responses. This study was undertaken to evaluate the effect of IL-10 on the adhesion of leukocytic cells to human umbilical vein endothelial cells. IL-10 inhibited the adhesion of a human monocytic cell line (THP-1) and a human lymphoblastic T-cell line (MOLT-4) to IL-1-stimulated endothelial cells. IL-10 also down-regulated the expression of ICAM-1 and VCAM-1 on IL-1-activated endothelial cells. IL-10-treated THP-1 cells adhered less than untreated THP-1 cells to IL-1-activated endothelial cells, whereas direct treatment of MOLT-4 had minimal effect on its adhesion to cytokine-activated endothelial cells. These results suggest that IL-10 counteracts the pro-inflammatory effects of IL-1 and regulates the adhesion of leukocytic cells to endothelial cells.

Pentoxifylline inhibits ICAM-1 expression and chemokine production induced by proinflammatory cytokines in human pulmonary epithelial cells

Airway epithelium participates in inflammatory reactions by producing chemokines and expressing cell-surface adhesion molecules which aid in the selective recruitment of effector cells. Previous studies showed that proinflammatory cytokines, interleukin 1 (IL-1) and tumor necrosis factor alpha (TNF alpha), induce surface expression of intercellular adhesion molecule 1 (ICAM-1) and the production of the chemokines interleukin 8 (IL-8) and monocyte chemoattractant protein (MCP-1) on pulmonary epithelial cell lines in vitro. In this study, the dose response of four cytokines, IL-1alpha, IL-1beta, TNF alpha and TNF beta, in inducing ICAM-1 expression and production of IL-8 and MCP-1 on pulmonary A549 epithelial cells was examined. Both IL-1alpha and IL-1beta induced ICAM-1 expression and IL-8 and MCP-1 production at lower doses than TNF alpha or TNF beta. Pentoxifylline, an anti-inflammatory agent used to treat vascular diseases, was tested for its ability to inhibit the activation of airway epithelial cells by these cytokines. Pentoxifylline completely inhibited the surface expression of ICAM-1 and the production of IL-8 and MCP-1 by cytokine-activated epithelial cells. As elevated levels of chemokines are often present in bronchial lavage fluids of patients suffering from various acute respiratory diseases, pentoxifylline may be useful for preventing the rapid development of immune reactions leading to lung injury.

Induction of CC chemokines in human peripheral blood mononuclear cells by staphylococcal exotoxins and its prevention by pentoxifylline

We investigated the inflammatory processes that might be associated with the arthrogenic activity of Staphylococcus aureus, the principal causative agent of bacterial arthritis. Human peripheral blood mononuclear cells (PBMC) were stimulated with the staphylococcal toxic shock syndrome toxin‐1 (TSST‐1) or enterotoxin B (SEB) and the production of chemokines was examined. Both TSST‐1 and SEB induced high levels (ng/mL) of MIP‐1α, MIP‐1β, and MCP‐1. The induction of these chemokines occurred mostly by direct stimulation of PBMC with staphylococcal exotoxins (SE), without requiring the intervention of IL‐1 and TNF‐α. The production of SE‐induced chemokines was blocked partially by anti‐DR and anti‐CD2 antibodies. Cell separation revealed monocytes as the cell source of these chemokines. However, addition of purified T cells amplified the levels of chemokine produced, suggesting that cognate interaction of SE bound on antigen‐presenting cells with T cells also contributes to chemokine production. The activation and recruitment of leukocytes by these chemokines may contribute to the pathophysiology of septic arthritis caused by staphylococci in humans through tissue injury and the recruitment of T lymphocytes, perhaps also initiating autoimmune responses. Pentoxifylline, an anti‐inflammatory agent, completely inhibited the production of these chemokines. J. Leukoc. Biol. 66: 158–164; 1999.

Stimulant-Dependent Modulation of Cytokines and Chemokines by Airway Epithelial Cells: Cross Talk between Pulmonary Epithelial and Peripheral Blood Mononuclear Cells

ABSTRACT Staphylococcal exotoxins (SE) and lipopolysaccharide (LPS) stimulate cells of the immune system to produce proinflammatory cytokines and chemokines which mediate septic shock and acute lung inflammation. A coculture of human peripheral blood mononuclear cells (PBMC) and pulmonary A549 epithelial cells was used to investigate inflammatory responses triggered by staphylococcal enterotoxin B (SEB), toxic shock syndrome toxin 1, and LPS. The levels of interleukin 1β (IL-1β), IL-6, gamma interferon-inducible protein 10, monocyte chemotactic protein 1 (MCP-1), macrophage inflammatory protein 1α, and RANTES were enhanced by 3.8-, 4.2-, 3.1-, 8.9-, 2-, and 2.9-fold, respectively, in cocultures of SEB-stimulated cells compared to in SEB-stimulated PBMC. In LPS-stimulated cocultures, only MCP-1 and RANTES levels were increased. These data suggest that the modulation of specific cytokines and chemokines is dependent on the stimulus and that there is bidirectional interaction between PBMC and lung epithelial cells to influence the immune response to these different stimuli.

Pirfenidone Blocks the In Vitro and In Vivo Effects of Staphylococcal Enterotoxin B

ABSTRACT Pirfenidone [5-methyl-1-phenyl-2-(1H)-pyridone] down-regulates expression of cytokines and other mediators involved in the onset and development of pulmonary fibrosis. Pirfenidone also inhibits production of tumor necrosis factor alpha (TNF-α) from macrophages incubated with endotoxin and protects mice against endotoxin shock. Pirfenidones ability to reduce cytokine expression in these disorders led us to investigate the drugs effect on another cytokine anomaly, superantigen-induced shock. BALB/c mice were exposed to staphylococcal enterotoxin B (SEB) either systemically or by aerosol and subsequently potentiated with a sublethal dose of lipopolysaccharide. In these experiments, pirfenidone given 2 to 4.25 h after SEB resulted in 80 to 100% survival versus only 0 to 10% survival among untreated control animals. Relative to serum cytokine levels from controls given toxin but no drug, there was a 35 to 80% decrease in TNF-α, interleukin 1, and other proinflammatory cytokines. In vitro experiments with human peripheral blood lymphocytes revealed that pirfenidone reduced SEB-induced cytokine levels 50 to 80% and inhibited 95% of SEB-induced T-cell proliferation. Overall, these studies demonstrated the potential utility of pirfenidone as a therapeutic against septic shock and the biological effects of SEB.

Staphylococcal enterotoxin B mutants (N23K and F44S): biological effects and vaccine potential in a mouse model.

Superantigens produced by Staphylococcus aureus can cause food poisoning and toxic shock syndrome. The biological activities and vaccine potential of mutant staphylococcal enterotoxin B (SEB) proteins, N23K and F44S, were studied in a lipopolysaccharide-potentiated mouse model. Although 10 micrograms of SEB per mouse is equivalent to 30 LD50, the same intraperitoneal dose of either mutant protein was nonlethal and did not elevate serum levels of tumor necrosis factors (TNF). N23K, F44S, and SEB were serologically identical in an enzyme-linked immunosorbent assay with polyclonal anti-SEB. Immunization with alum containing N23K, F44S, or SEB elicited an anti-SEB response that protected 80-87% of the mice against a 10 micrograms SEB challenge. Controls lacking an anti-SEB titer did not survive. Pooled sera from immunized mice effectively blocked SEB-induced T-cell proliferation in vitro. Naive mice survived a lethal SEB challenge when given pooled antisera 1, 2, or 4 h later, whereas the antisera failed to protect animals when administered 6 or 8 h after the toxin. Lethality at the later times was consistent with increased serum levels of TNF observed 6 h after SEB injection. These studies suggest that the N23K and F44S mutant proteins of SEB are less biologically active than the wild-type toxin, yet retain epitopes useful for eliciting a protective antibody response.

The staphylococcal enterotoxin (SE) family: SEB and siblings.

Staphylococcus aureus plays an important role in numerous human cases of food poisoning, soft tissue, and bone infections, as well as potentially lethal toxic shock. This common bacterium synthesizes various virulence factors that include staphylococcal enterotoxins (SEs). These protein toxins bind directly to major histocompatibility complex class II on antigen-presenting cells and specific Vβ regions of T-cell receptors, resulting in potentially life-threatening stimulation of the immune system. Picomolar concentrations of SEs ultimately elicit proinflammatory cytokines that can induce fever, hypotension, multi-organ failure, and lethal shock. Various in vitro and in vivo models have provided important tools for studying the biological effects of, as well as potential vaccines/therapeutics against, the SEs. This review succinctly presents known physical and biological properties of the SEs, including various intervention strategies. In particular, SEB will often be portrayed as per biodefense concerns dating back to the 1960s.

Update on Staphylococcal Superantigen-Induced Signaling Pathways and Therapeutic Interventions

Staphylococcal enterotoxin B (SEB) and related bacterial toxins cause diseases in humans and laboratory animals ranging from food poisoning, acute lung injury to toxic shock. These superantigens bind directly to the major histocompatibility complex class II molecules on antigen-presenting cells and specific Vβ regions of T-cell receptors (TCR), resulting in rapid hyper-activation of the host immune system. In addition to TCR and co-stimulatory signals, proinflammatory mediators activate signaling pathways culminating in cell-stress response, activation of NFκB and mammalian target of rapamycin (mTOR). This article presents a concise review of superantigen-activated signaling pathways and focuses on the therapeutic challenges against bacterial superantigens.