Antigens are found

Dear student,
Antigen refers to any foreign substance which on entering the body stimulates the production of antibodies in the body of the individual as a part of the immune response. These foreign substances can be toxins, bacteria, virus, foreign blood cells or the cells of the transplanted organs.
Genes do not necessarily produce antigens.
​​​Antigens are not produced. They invade or enter body.

Regards.