[Cross allergies].

The first descriptions of crossed allergenicity were concerned with the associations between Pollen/Food allergy: birch pollen/apple, grass pollen/wheat-tomato etc. Since then other crossed reactions have been described, involving pneumoallergens, tropallergens, drugs, hymenoptera venoms. Crossed reactions are the combination of an antigen with a recognition molecule other than that which stimulated its synthesis, because of epitope(s) that are common or sufficiently close between two antigens. The techniques of immunoprints and RAST inhibition give confirmation of crossed reactions that are suspected clinically.