Crossreactions

Crossreactions, or cross-reactivity, describe a situation in which immune responses to one antigen also recognize and respond to a related but distinct antigen. This occurs when antibodies or T cell receptors bind to epitopes that are shared or structurally similar between different molecules, even if the antigens are not identical.

Several mechanisms underlie cross-reaction. Shared linear or conformational epitopes can be recognized by the same antibody or receptor. Carbohydrate determinants or conserved structural motifs can also drive cross-binding. In some cases, a polyclonal immune response produces a range of antibodies with different specificities, increasing the chance of cross-reactivity. Cross-reactions can occur in both humoral and cellular immunity and may be influenced by affinity and concentration of the immune components involved.

In practice, cross-reactions have important implications for diagnostics and clinical outcomes. Serologic tests may yield false-positive results when antibodies bind related non-target antigens. In allergies, cross-reactivity between pollen proteins and certain foods can trigger oral allergy syndrome in sensitized individuals. In infectious disease serology, antibodies raised against one pathogen can react with antigens from related organisms, complicating interpretation. Cross-reactivity can also be involved in autoimmune phenomena through molecular mimicry, where immune recognition of a pathogen epitope resembles self-t proteins, potentially contributing to autoimmune disease.

Management strategies include using highly specific antigens in tests, employing adsorption or competitive inhibition assays to distinguish true from cross-reactive signals, and careful interpretation of results in the clinical context. See also cross-reactivity and molecular mimicry for related concepts.