Closely related allergen species often exhibit some degree of cross-reactivity. In general, plant species within the same taxonomic family may be substantially, though not completely, cross-reactive. Additionally, there are several allergenic proteins which are common across unrelated species known as “pan-allergens”. For some patients, these proteins can generate an IgE immune response and contribute to broad cross-reactivity profiles including the occurrence of certain food allergies.
The basis of cross-reactivity is the biochemistry of the immune response. The “language” of molecular interaction is based on molecular structure, which is what is detected by the immune system through its antibodies. When IgE antibodies react with foreign proteins, they cause an allergic response and are kept in circulation to become part of the immune system’s adaptive memory. These retained IgE antibodies are now primed for a specific protein configuration and may be triggered by other proteins that have similar, though not identical, configuration.
The degree of structual similarity determines the degree of cross-reactivity. Since protein configurations are determined by the arrangement of amino acid components, which are in turn based on the DNA sequence for that protein, it may be assumed that related species tend to have proteins with similar configurations. Since DNA sequences are conserved along evolutionary lines, you are likely to see patterns of cross-reactivity along taxonomic lines.
Taxonomic hierarchies go in the following order of increasing relatedness and similarity: Family – Genus – Species.
For more infomation on how these hierarchies can affect cross-reactivity among botanical species, review the sections on Taxonomy.