Identification of Staphylococcal Enterotoxin B Domains Involved in Binding to Cultured Human Kidney Proximal Tubular Cells: Imparting Proliferation and Death

Staphylococcal Enterotoxin Superantigens Induce Prophylactic Antiviral Activity Against Encephalomyocarditis Virus In Vivo and In Vitro

The staphylococcal enterotoxins (SEs) are classified as superantigens due to their potent stimulation of the immune system resulting in T cell activation and prodigious cytokine production and toxicity. This study examined the ability of superantigens to induce prophylactic antiviral activity in vivo and in vitro and evaluated potential superantigen mimetic peptides. Prophylactic treatment of mice in vivo with intraperitoneal injections of SE superantigens SEA and SEB (both at 20 μg/day for 3 days) prevented encephalomyocarditis virus (EMCV)-induced lethality in 100% and 80% of mice, respectively, as compared with control saline-treated groups in which EMCV was lethal to all mice. Furthermore, SEA (2 μg/mL) and SEB (1 μg/mL) induced antiviral activity in mouse splenocytes to produce an antiviral factor since their supernatant prevented EMCV lysis of L929 cells in tissue culture. It was found that superantigens do not directly prevent EMCV infection, but rather indirectly through inducing interferon gamma (IFNγ) production in cells as the antiviral factor. Evaluation of various superantigen mimetic peptides showed that one peptide (SEA3) had superantigen-like activity by inducing IFNγ production in cells but without the cellular proliferation, as associated with superantigens. However, the induction of IFNγ activation by the SEA3 peptide was not as pronounced, and took a much higher peptide concentration, when compared with the parent superantigen. If the negative side effects of superantigens can be eliminated, their beneficial properties can be harnessed for prophylactic treatment of viral infections and other pathologies requiring a robust immune response.

Sphingolipids and Redox Signaling in Renal Regulation and Chronic Kidney Diseases

Significance: Sphingolipids play critical roles in the membrane biology and intracellular signaling events that influence cellular behavior and function. Our review focuses on the cellular mechanisms and functional relevance of the cross talk between sphingolipids and redox signaling, which may be critically implicated in the pathogenesis of different renal diseases. Recent Advances: Reactive oxygen species (ROS) and sphingolipids can regulate cellular redox homeostasis through the regulation of NADPH oxidase, mitochondrial integrity, nitric oxide synthase (NOS), and antioxidant enzymes. Over the last two decades, there have been significant advancements in the field of sphingolipid research, and it was in 2010 for the first time that sphingolipid receptor modulator was exploited as a therapeutic in humans. The cross talk of sphingolipids with redox signaling pathways becomes an important mechanism in the development of many different diseases such as renal diseases. Critical Issues: The critical issues to be addressed in this review are how sphingolipids interact with the redox signaling pathway to regulate renal function and even result in chronic kidney diseases. Ceramide, sphingosine, and sphingosine-1-phosphate (S1P) as main signaling sphingolipids are discussed in more detail. Future Directions: Although sphingolipids and ROS may mediate or modulate cellular responses to physiological and pathological stimuli, more translational studies and mechanistic pursuit in a tissue- or cell-specific way are needed to enhance our understanding of this important topic and to develop effective therapeutic strategies to treat diseases associated with redox signaling and sphingolipid cross talk. Antioxid. Redox Signal. 28, 1008-1026.

Blood Groups in Infection and Host Susceptibility

Blood group antigens represent polymorphic traits inherited among individuals and populations. At present, there are 34 recognized human blood groups and hundreds of individual blood group antigens and alleles. Differences in blood group antigen expression can increase or decrease host susceptibility to many infections. Blood groups can play a direct role in infection by serving as receptors and/or coreceptors for microorganisms, parasites, and viruses. In addition, many blood group antigens facilitate intracellular uptake, signal transduction, or adhesion through the organization of membrane microdomains. Several blood groups can modify the innate immune response to infection. Several distinct phenotypes associated with increased host resistance to malaria are overrepresented in populations living in areas where malaria is endemic, as a result of evolutionary pressures. Microorganisms can also stimulate antibodies against blood group antigens, including ABO, T, and Kell. Finally, there is a symbiotic relationship between blood group expression and maturation of the gastrointestinal microbiome.

Ceramide-induced apoptosis in renal tubular cells: a role of mitochondria and sphingosine-1-phoshate

Ceramide is synthesized upon stimuli, and induces apoptosis in renal tubular cells (RTCs). Sphingosine-1 phosphate (S1P) functions as a survival factor. Thus, the balance of ceramide/S1P determines ceramide-induced apoptosis. Mitochondria play a key role for ceramide-induced apoptosis by altered mitochondrial outer membrane permeability (MOMP). Ceramide enhances oligomerization of pro-apoptotic Bcl-2 family proteins, ceramide channel, and reduces anti-apoptotic Bcl-2 proteins in the MOM. This process alters MOMP, resulting in generation of reactive oxygen species (ROS), cytochrome C release into the cytosol, caspase activation, and apoptosis. Ceramide regulates apoptosis through mitogen-activated protein kinases (MAPKs)-dependent and -independent pathways. Conversely, MAPKs alter ceramide generation by regulating the enzymes involving ceramide metabolism, affecting ceramide-induced apoptosis. Crosstalk between Bcl-2 family proteins, ROS, and many signaling pathways regulates ceramide-induced apoptosis. Growth factors rescue ceramide-induced apoptosis by regulating the enzymes involving ceramide metabolism, S1P, and signaling pathways including MAPKs. This article reviews evidence supporting a role of ceramide for apoptosis and discusses a role of mitochondria, including MOMP, Bcl-2 family proteins, ROS, and signaling pathways, and crosstalk between these factors in the regulation of ceramide-induced apoptosis of RTCs. A balancing role between ceramide and S1P and the strategy for preventing ceramide-induced apoptosis by growth factors are also discussed.

Characterization of the interaction of staphylococcal enterotoxin B with CD1d expressed in human renal proximal tubule epithelial cells

Background

Participation of renal cells in the pathogenesis of staphylococcal enterotoxin B (SEB) is critical for late cleansing and sequestration of the antigens facilitated by CD1d mediated antigen sensing and recognition. This is a noted deviation from the typical antigen recognition process that recruits the major histocompatibility complex class II (MHC II) molecules. The immunological importance of CD1d is underscored by its influences on the performances of natural killer T-cells and thereby mediates the innate and adaptive immune systems.

Results

Using diffraction-based dotReady™ immunoassays, the present study showed that SEB directly and specifically conjugated to CD1d. The specificity of the conjugation between SEB and CD1d expressed on human renal proximal tubule epithelial cells (RPTEC) was further established by selective inhibition of CD1d prior to its exposure to SEB. We found that SEB induced the expression of CD1d on the cell surface prompting a rapid conjugation between them. The mRNA transcripts encoding CD1d remained elevated potentially after completing the antigen cleansing process.

Conclusion

Molecular targets associated with the delayed pathogenic response have essential therapeutic values. Particularly in the event of bioterrorism, the caregivers are typically able to intervene much later than the toxic exposures. Given circumstances mandate a paradigm shift from the conventional therapeutic strategy that counts on targeting the host markers responding to the early assault of pathogens. We demonstrated the role of CD1d in the late stage of pathogen recognition and cleansing, and thereby underscored its clinical potential in treating bioweaponizable antigens, such as Staphylococcal enterotoxin B (SEB).

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-015-0344-5) contains supplementary material, which is available to authorized users.

Staphylococcus aureus enterotoxins A- and B: binding to the enterocyte brush border and uptake by perturbation of the apical endocytic membrane traffic

Enterotoxins of Staphylococcus aureus are among the most common causes of food poisoning. Acting as superantigens they intoxicate the organism by causing a massive uncontrolled T cell activation that ultimately may lead to toxic shock and death. In contrast to our detailed knowledge regarding their interaction with the immune system, little is known about how they penetrate the epithelial barrier to gain access to their targets. We therefore studied the uptake of two staphylococcal enterotoxins (SEs), SEA and SEB, using organ cultured porcine jejunal explants as model system. Attachment of both toxins to the villus surface was scarce and patchy compared with that of cholera toxin B (CTB). SEA and SEB also bound to microvillus membrane vesicles in vitro, but less efficiently than CTB, and the binding was sensitive to treatment with endoglycoceramidase II, indicating that a glycolipid, possibly digalactosylceramide, acts as cell surface receptor at the brush border. Both SEs partitioned poorly with detergent resistant membranes (DRMs) of the microvillus, suggesting a weak association with lipid raft microdomains. Where attachment occurred, cellular uptake of SEA and SEB was also observed. In enterocytes, constitutive apical endocytosis normally proceeds only to subapical early endosomes present in the actomyosin-rich "terminal web" region. But, like CTB, both SEA and SEB penetrated deep into the cytoplasm. In conclusion, the data show that after binding to the enterocyte brush border SEA and SEB perturb the apical membrane trafficking, enabling them to engage in transcytosis to reach their target cells in the subepithelial lamina propria.