Flexi Says: Immunodeficiency occurs when one or more components of the immune system are not working normally. As a result, the ability of the immune system to respond to pathogens and other threats is decreased. A person with immunodeficiency may suffer from frequent life-threatening infections. In other words, an individual with a compromised immune system (for example, a person with AIDS) may be unable to fight off and survive infections by microorganisms that are usually benign. Immunodeficiency can be present at birth or acquired after birth.