Cross reactivity explained

A common query on FoodPrint reports is why a food stimulates a high number of IgG antibodies and appears as an ELEVATED or BORDERLINE response when it has not been eaten.

There may be several reasons. Initially, we would discuss whether the food is ‘hidden’, and therefore eaten, within packaged and processed products consumed by the client. This is a common occurrence with some foods such dairy, egg and wheat. Uncommonly, the food may be hidden in supplements e.g., ginger or turmeric or seaweeds in green smoothies. If not detected, then cross reactivity would be explored. 

Cross reactivity commonly occurs within food groups and species, but it may also occur between food and non-food sources such as, for example, house dust mites cross reacting with molluscs and crustaceans. Cross reactivity relates to the similar protein structures within these foods and non-foods. 

A unique antibody, an IgG antibody, synthesised to identify and attach onto one food or non-food, specifically the proteins located on the surface of that food or non-food, binds onto another protein (or antigen) if their structures are almost identical. The IgG antibody is the key that fits the protein lock, and an immune system response is initiated. Please see Diagram 1.  

In simpler terms, the immune system confuses similar protein structures and may react to, for example, Brazil nuts when not eaten, whereas other nuts with almost identical protein structures such as cashews, pistachios and almonds have been eaten. When the blood sample is exposed to the Brazil nut protein imprinted on the food panel on a FoodPrint test, the IgG antibodies stimulated in response to the other nuts eaten, will attach to the Brazil and show an elevated response. 

What is an antibody? An antibody (or immunoglobulin) is a protective Y-shaped protein that is manufactured by the immune system in direct response to the detection of a foreign substance within the bloodstream. The immune system produces five different types of antibodies: IgA, IgD, IgE, IgG and IgM, each of these having their own specific function and mechanism of action in relation to protecting the body. With relevance to food sensitivity and cross-reactivity, a FoodPrint test detects IgG antibodies, which make up approximately 75% of all antibodies within the human body including the bloodstream.  

Once produced, and IgG antibodies are stimulated if a food or substance has been ingested only once in a lifetime, they recognise and latch onto their identikit protein (antigen) with the aim of removing it from the body. In this way all non-self proteins are ‘checked’ by the immune system and their elimination is initiated.  

We have an information sheet available to practitioners on our website under Educational Resources. Due to the potential complexity of the subject this is not available to the general public.