apparent antigens are actually a mixture of macromolecules (for example, from pathogens, toxins, proteins, or pollen) comprising several epitopes. Contact with a complex antigen such as a virus will stimulate multiple immune responses to the virus' different macromolecules as well as the individual epitopes of each macromolecule. For example, the tetanus toxin is a single protein macromolecular antigen but will stimulate many immune responses due to the tertiary structure of the protein yielding many different epitopes. The toxin that creates the immune response will have an epitope on it that stimulates the response. Denaturing the protein may 'disarm' its function but allow the immune system to have an immune response thus creating an immunity without harming the patient. Cross reactivity has implications for flu vaccination because of the large number of strains of flu, as antigens produced in response to one strain may confer protection to different strains. Cross-reactivity need not be between closely related viruses, however; for example, there is cross-reactivity between influenza virus-specific CD8+ T cells and hepatitis C virus antigens. Allergies Cross reactivity may also occur between a pathogen and a protein found on a non-pathogen (i.e. food.) There may even be cross reactivity between two non-pathogens; for example, Hevein-like protein domains are a possible cause for allergen cross-reactivity between latex and banana. Cross-reactivity may be caused by identical carbohydrate structures on unrelated proteins from the same or different species. Such cross-reactive carbohydrate determinants (CCDs) are an issue in allergy diagnosis, where about a fifth of all patients displays IgE antibodies against Asn-linked oligosaccharides (N-glycans) containing core α1,3-linked fucose. As CCDs apparently do not elicit allergic symptoms, a positive in vitro test based on IgE binding to CCDs must be rated as false positive. References External links Chemical reactions Immune system