Detecting Allergens in Foods Miriam Rittenberg

What are allergies? -one way your body detects foreign substances is with different antibodies that bind to proteins from those materials (antigens), and then trigger an immune response -several antibodies in the body but the one involved in allergic reactions is IgE (short for Immunoglobulin E) -it mostly helps the body fight parasitic worms -not much IgE is floating around by itself, it is mostly bound to mast cells -in some people IgE will attach to harmless proteins (allergens) -allergies are partially genetic but what causes someone to have an allergy is still poorly understood -allergies vary from person to person

Allergic Reaction -allergen attaches to IgE on mast cells -the mast cells release a lot of chemicals including histamine -these increase permeability of blood vessels -this is supposed to let white blood cells travel in and out of blood vessels -but it also lowers blood pressure which can be dangerous

Why is a detector useful? -no cure for allergies so people with them need to avoid foods with allergens they are sensitive to -usually this can be done by looking at the list of ingredients -but sometimes foods can be mislabeled, or an ingredients list might not be available -so it would be helpful to have a portable and easy to use way to check foods for ingredients that might contain allergens -an iGem team decided to make one for peanuts -peanuts are not the most common food allergy but they are the one that causes the most cases of anaphylaxis

What the iGem team’s detector is checking for -not everybody with an allergy reacts to the same allergen -but if a food has one peanut allergen it probably has the others too -so checking for one is enough -this detector checks for the protein Ara h1 (called this because another name for peanuts is Arachis hypogaea) -other allergens in peanuts are called Ara h2, Ara h3, etc.

Parts of the detector: -an epitope from Ara h1 -an epitope is the specific part of an antigen that the antibody will bind to -a fluorescent protein bound to the epitope -this is red fluorescent protein (RFP) -an antibody that targets Ara h1 -this will be a kind of IgE but different variants of IgE bind to different proteins -a different fluorescent protein bound to the antibody -this is fluorescein isothiocyanate (FITC) -an electrical system that can excite the FITC and measure the wavelength of the light emitted by the detector

-the FITC will transfer energy to the RFP How the detector works -if there is no Ara h1 for the antibody to bind to, the antibody will bind to the synthetic epitope -this will bring the two fluorescent proteins close enough to interact with each other -the FITC will transfer energy to the RFP -this causes the RFP to emit a different wavelength of light -the detector will detect this wavelength and turn on a green light indicating that there are no peanuts in the detector No Ara h 1  Antibody Epitope RFP FITC Higher wavelength Energy

-the antibody will bind to the Ara h1 What if there is Ara h1? -the antibody will bind to the Ara h1 -the FITC and the RFP will stay far apart -the RFP emits the wavelength of light that it does by itself -the detector notices the change and turns on a red light -there are peanuts in the detector Ara h 1 is present Antibody Ara h 1 Epitope FITC RFP Lower wavelength

Conclusion -similar devices could be created for other allergens -one thing to worry about is that this tests for one molecule to decide whether any of many molecules are present -if a food had no Ara h1, but did have other peanut allergens, someone could have a reaction to the food even though this detector stayed green -unlikely to be a problem in this case because peanuts always have Ara h1, but it is something to keep in mind

Sources http://2015.igem.org/Team:Linkoping_Sweden http://www.jacionline.org/article/S0091-6749(02)91380-1/fulltext http://onlinelibrary.wiley.com/doi/10.1046/j.1365-2222.1998.00301.x/abstract https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3206235/ https://www.cdc.gov/nchs/products/databriefs/db10.htm https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3122150/ https://www.rsb.org.uk/biologist-features/158-biologist/features/1512-focus-on-allergies (this is the source of the diagram in slide 3)