Submitted to: Toxins
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/7/2019
Publication Date: 7/10/2019
Citation: Rasooly, R., Do, P.M., He, X., Hernlem, B.J. 2019. T cell receptor Vß9 in method to rapidly detect active staphylococcal enterotoxin type A without live animals. Toxins. 11:399. https://doi.org/10.3390/toxins11070399.
Interpretive Summary: One of the major sources of food poisoning is caused by eating foods contaminated with Staphylococcal enterotoxins (SEs) made by bacteria. SEA is one kind of this toxin that is often found in outbreaks of food poisoning. The toxin can be made inactive but still detectable by some tests, so it is the active form that is important to detect in food to protect consumers. Live animals have been used to detect active toxin, but this is disfavored for legal and ethical reasons. In this study we found that a protein, TCR-Vß9, found on some white blood cells, known as T-cells, can be used to detect SEA. The test needs also another type of white blood cell known as a B-cell and we came up with a method using so-called cell lines of both cell types to specifically detect SEA but not the related toxins SED and SEE. We also found and showed, that the T-cells produce chemicals called cytokines in response to SEA and this happens even when the B-cells are dead. This work is important for food safety and protecting consumers.
Technical Abstract: Staphylococcal food poisoning is a result of ingestion of Staphylococcal enterotoxins (SEs) produced by Staphylococcus aureus, a major bacterial pathogen that produces more than 23 varieties of staphylococcal enterotoxins (SEs), the causative agent of food poisoning. Staphylococcal enterotoxin type A (SEA) is the predominant toxin produced by S. aureus strains isolated from food poisoning outbreak cases. For public safety, assays to detect and quantify SEA ideally respond only to the active form of the toxin and this usually means employing disfavored live animal testing which suffer also from poor reproducibility and sensitivity. We developed a cell-based assay for SEA quantification in which biologically active SEA is presented by Raji B-cells to CCRF-CEM T-cells resulting in decreased expression of Vß9 within two hours with dose dependency over a 6-log range of SEA concentration. This bioassay can discern biologically active SEA from heat inactivated SEA. This assay is specific to SEA with no cross reactivity to the homologically similar SED or SEE. In this study we terminated any ongoing biochemical reactions in accessory cells while retaining the morphology of the antigenic sites by using paraformaldehyde fixation and challenge the current model for mechanism of action of the SEA superantigen. We demonstrated for the first time that although fixed, dead accessory cells having no metabolic functions to process the SEA superantigen into short peptide fragments for display on their cell surface, can instead present intact SEA to induce T-cell activation which leads to cytokine production. However, the level of cytokine secretion by intact SEA was statistically significantly lower than with viable accessory cells, which have the ability to internalize and process of the SEA superantigen.