An antibody is a protein that the immune system sends out as a response to antigens, which are harmful substances, explains MedlinePlus. There are different types of antibodies; and, they each fight against only one particular type of antigen. Some antigens are intrusive foreign objects, such as bacteria, viruses or chemicals. However, the body can also form antigens, such as harmful tissue cells or bacterial toxins.
Plasma cells, a specific type of B-cells, are responsible for the production of antibodies, reports Wikipedia. An autoimmune disorder can occur when the immune system sends antibodies to attack tissue that is healthy. A B-cell can have more than 50,000 antibodies on its surface; and, these antibodies bind to antigens in large groups. The bind between an antibody and an antigen is reversible.
There are several different classifications of antigens, including endogenous antigens, auto-antigens and exogenous antigens. Neoantigens, viral antigens and tumor antigens are also all types of antigens. Exogenous antigens come from outside the body and enter through inhalation or injection. Endogenous antigens come from within normal cells in the body. Autoantigens are normal proteins that the immune system attacks in patients suffering from autoimmune disorders. Tumor antigens come from the surface of tumor cells.