Immune Responses -
The injection of an antigen into an animal may initiate several important changes in the animal. The first response is to eliminate the antigen through extensive phagocytosis in the liver, lung and spleen, so that nearly 90% of the antigen is removed from the circulation in about 10 to 20 minutes of its introduction.

In the second phase, which lasts for about 4 to 7 days, the antigen is eliminated by enzymic hydrolysis and digestion. However, the most important phase in antigen elimination is the immune response involving formation of antibodies, which provide resistance to the animal body against infection.