Staphylococcal Enterotoxins

In addition to their nature as superantigens, SEs function as potent gastrointestinal toxins causing SFP, which has a major public health impact.[1,3-5] Superantigenicity and emesis activities of SEs have been shown to result from distinct regions of the toxin protein. SEs comprise a family of homologous but antigenically different exotox-ins, which are heat stable and resistant to inactivation by gastrointestinal proteases. SEs have also been implicated in several allergic and autoimmune diseases. The repertoire of SEs includes the five classical enterotoxins SEA through SEE and the more recently identified enterotoxins starting with SEG (Table 1). To date, the ''alphabet'' of SEs and their coding genes has reached the letter ''Q.'' However, some of the recently described SEs were shown to be nonemetic, thus actually lacking the defining property of SEs. Nevertheless, the standard convention hitherto has been to refer to proteins exhibiting sequence similarity to SEs as enterotoxins.

For some SEs, slightly divergent sequences and minor epitope differences are known, resulting in their further subdivision.[5] SEC comprises several unique molecular variants named SEC1, SEC2, and SEC3 as well as variants produced by animal-adapted strains of S. aureus and S. intermedius, such as ovine (SECovjne), bovine (SECbovine), and canine (SECcanine) types. In addition, variants of SEG are known.

Different S. aureus strains harbor different combinations of PTSAgs.[6] The majority of the SE-encoding genes are located on mobile genetic elements [plasmids,

Superantigen

Superantigen

Antigen T-cell receptor

MHC class II molecule

MHC class II molecule

Fig. 1 Schematic representation of the different interactions of antigens and superantigens with the MHC class II molecule and the T-cell receptor.

Fig. 1 Schematic representation of the different interactions of antigens and superantigens with the MHC class II molecule and the T-cell receptor.

prophages, and pathogenicity islands, e.g., SaPIl (prototype), SaPI3, SaPI4, SaPIbov] except for the genes that encode SEG, SEH, and SEI, which are chromosomal. Analyzing the seg-sei intergenic and flanking regions, Jarraud et al.[7] found a highly prevalent operon encoding— in addition to SEG and SEI—further enterotoxins, designated SEK, SEL, and SEM. SEK and SEL were renamed subsequently as SEN and SEO, respectively. Phylogenetic analysis of all hitherto known SE genes indicates that they all potentially derived from this operon (named the enterotoxin gene cluster, egc), inferring that egc is in an SE gene nursery. Constructing phylogenetic trees from nucleic acid and amino acid sequences, respectively, three monophyletic groups were identified by Jarraud et al.: one composed of sea, sed, see, seh, sej, sen, and seo; another including seb, sec, and seg; and a third comprising sei and sem.[7]

Getting Started With Dumbbells

Getting Started With Dumbbells

The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.

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