Answer:
Antibodies.
Step-by-step explanation:
An antibody is a protein produced by the white blood cells of an organism to resist harmful foreign substances, so-called antigens. Once the body has done this once against an antigen, it will usually develop immunity to the disease that the antigen represents. A common vaccination method is to supply the body with small amounts of unknown antigens, thus stimulating the body to produce anti-inflammatory antibodies. In some cases, antibodies can react to harmless substances, causing an allergic reaction.