NO
NO
Antigen
This substance has a general name called an antigen.
An allergy is a hypersensitivity to an environmental antigen (allergen). If a person has a hypersensitivity to an antigen they will have a patholigic (disease) response when exposed to that antigen. When the hypersensitive individual is initially exposed to the antigen, they will produce allergen specific antibodies, primarily immunoglobulin E (IgE), that will during subsequent exposures bond with membrane proteins on the mast cell membrane. This bonding allows degranulation (the release of stored chemicals) of the mast cell. Mast cells manufacture and store chemicals, including histamine, that are responsible for the affects of inflamation.
The antibody is specific to the antigen (allergen). Different antibodies are produced at different times of exposure (IgM=acute; IgG=longterm) or in different systems of the body (IgA is produced in the gut).
Some more context would be helpful. This question sounds like it may be asking about antigen exposure in the field of allergic disease, but it's hard to be sure. Hypersensitivity reactions (the immune system basis for allergies) are based on the principle that allergy follows initial sensitization to an antigen.
An antigen is called an allergen when it triggers an abnormal immune response that leads to allergic reactions in sensitive individuals. This typically occurs when the immune system mistakenly identifies a harmless substance, such as pollen, pet dander, or certain foods, as a threat. The ensuing immune response can cause symptoms ranging from mild (like sneezing or itching) to severe (such as anaphylaxis). Essentially, allergens provoke an exaggerated response from the immune system, distinguishing them from other antigens that do not elicit such reactions.
Antigens.
Abwehrstoff or Antigen
the antigen must bind to the receptor
An allergy is the reaction that the body will have, where as an allergen is something that causes the allergy to occur.
The O antigen is not an antigen that may be found on the surface of an erythrocyte. A and B antigens are present in the ABO blood group system, while the Rh antigen is part of the Rh blood group system. O blood type individuals lack A and B antigens on their red blood cells.