Antigens are not viruses, they are two concepts. A virus is a pathogenic microorganism that has the potential to infect the body and cause disease, while an antigen is relative to the body’s immune system. Antigens can be derived from viruses, from bacteria, or even from substances in your own body, and this is the mechanism by which the immune system causes damage to itself and autoimmune disease occurs. A component of a virus can be an antigen, but a virus does not become an entire antigen. After a virus infects the body, it can have only one antigen-antibody system or multiple antigen-antibody systems. For example, if hepatitis C infects the body, the only corresponding tests are for antibodies to hepatitis C and antigens to hepatitis C. In the case of hepatitis B, it is possible to see three sets of antigen-antibody systems: surface antigens and antibodies, E antigens and antibodies, and core antigens and antibodies.