Our immune system's defense forces fight off many different pathogens ever day. There are several causes for a weakened immune system. It is often the result of an unhealthy lifestyle, but frequently also colds, chronic diseases and older age. Immunodeficiencies, however, occur because certain parts of the immune system are lacking, making those people more vulnerable to certain infections. Immunodeficiencies can either be heriditary or caused by disease. In this film we will find out how exactly the immune system works and how a weakened immune system or immunodeficiency comes about.