photoantigen

A photoantigen is a molecule that becomes antigenic, meaning it can provoke an immune response, only after it has been exposed to light. This light-induced alteration typically involves a chemical change within the molecule, such as the formation of a new chemical bond or a modification of its existing structure, which then renders it recognizable by the immune system as foreign. Without this light exposure, the molecule may be tolerated by the body or may not possess the necessary structural features to trigger a significant immune reaction.

The concept of photoantigens is particularly relevant in the study of phototoxic reactions and drug-induced photosensitivity. Certain drugs, when taken orally or applied topically, can accumulate in the skin. Upon exposure to ultraviolet (UV) radiation, these drugs can undergo photochemical reactions, forming photoantigens. These photoantigens can then bind to skin proteins, creating complexes that are recognized as foreign by T cells and other immune components. This immune response leads to inflammation, redness, itching, and sometimes blistering, characteristic of a photoallergic reaction. Unlike phototoxic reactions, which are direct damage to cells caused by a photosensitizing agent, photoallergic reactions involve a specific immune-mediated mechanism. Understanding photoantigens is crucial for diagnosing and managing these light-related adverse drug reactions and for developing strategies to mitigate their effects.