Food allergies are adverse reactions to an otherwise harmless food or food component that involves an abnormal response of the body's immune system to specific protein(s) in foods.
This is a beginning sentence of a paper on food allergies. I was wondering what the subject of the verb involves and have asked opinions from three English language experts who also have scientific knowledge, but their opinions vary. Their answers were as follows:
Person 1: The subject is food allergies and the verb should be involve.
Person 2: The subject is abnormal response and the verb should be involve.
Person 3: The subject is food or food component, so this sentence is correct. He also pointed out that the paper is written in British English (I showed him the following sentences and he got some clues from there) so here involves means evokes or causes.
Which of these opinions is the correct one?