MadSci Network: Immunology |
This is a very good question. Although any structure such as cocaine can be recognized by antibody as an antigen, usually only proteins can elicit fully developed adaptive immune responses because of their ability to engage the T cells. T cells can induce most antibody responses and are required for immunological memory. T cells recognize antigens as peptide fragments of proteins bound to major histocompatibility complex (MHC) molecules. The larger and more complex a protein, the more likely it is to elicit an immune response. Some small soluble proteins are unable to induce a response unless they are made to aggregate in some way. Cocaine is not a protein, and it is a very small and "simple" molecule. Therefore, it usually does not elicit an immune response. However, it can be attached covalently to a protein carrier such as keyhole limpet hemocyanin (KLH). The cocaine-KLH conjugate can be used to induce the antibodies that recognize cocaine. In your question, you also mentioned the exposure of nasal mucous membranes to cocaine and allergic responses. Allergens are antigens that commonly provoke an IgE antibody response. For the same reason, usually allergens must be proteins because only proteins induce T-cell responses. Thus, cocaine can not invoke an allergic reaction. Most allergens are soluble proteins that are inhaled in desiccated particles such as pollen grains. Your question is interesting because recently scientists are developing some vaccines that can be administered to the mucosa by nasal inhalation for respiratory infectious diseases. Maybe we can consider using a similar structure of cocaine (so-called "molecular mimicry") conjugated with an appropriate carrier protein for a nasal vaccine design!
Try the links in the MadSci Library for more information on Immunology.