crossreaction

Crossreaction, or cross-reactivity, is the ability of an immune component to recognize and bind to an antigen that is structurally similar to the one that elicited its response. In immunology and serology, antibodies and, less commonly, T cells may react with related antigens due to shared epitopes, motifs, or molecular patterns.

Crossreactivity arises from structural similarity among antigens, including conserved protein sequences, conformational epitopes, or shared carbohydrate determinants. It can result from molecular mimicry, polyreactive antibodies produced by B cells, or widespread crossreactive epitopes across related pathogens.

Examples include autoimmune consequences such as rheumatic fever, in which antibodies against Streptococcus pyogenes M protein cross-react with heart tissue; pollen-food syndrome, where IgE to certain pollens cross-reacts with fruit proteins; and serological cross-reactivity among related viruses such as dengue and Zika, which can complicate diagnostic interpretation.

Implications include potential false-positive results in diagnostic tests, challenges in vaccine design, and, in some cases, beneficial broad protection. Strategies to mitigate crossreactivity include using highly specific antigens, multiplex assays, or absorption tests to distinguish related antigens.