For the production of polyclonal antibodies, lab animals are immunized with a specific antigen. After a few weeks, its immune system produces a high level of antibodies against this specific antigen. These antibodies are collected in an antiserum of the animals. This antiserum contains antibodies from several clones of B cells. The antigen is injected twice or thrice with antigen to produce this antiserum. These injections stimulate memory cells that make IgG antibodies against the antigen. Most of the antigens having multiple epitopes produce multiple antibodies in the body of these animals.