The immune system's function is to respond to foreign pathogens and maintain defense mechanisms of the body. Inability of the immune system to react to pathogens and stimuli can cause immunlogical disorders and diseases.The immune system responses and divided into two categories: innate and adaptive.
The innate system is passive; it acts as the first line of defense. Surface barriers that are part of the innate system can be chemical, mechanical or biological – an example is skin, which prevents pathogens from entering the body. Once pathogens enter the body a non-specific response is produced, the innate system also has no immunological memory which means that repeated exposure will produce the same response. Pathogens are identified by receptors in entry pathways, when these receptors are compromised a signal is sent. The non-specific responses are cell-mediated and they involve phagocytes, lymphocytes and cytokines.
The second line of defense is the adaptive immune system which is trigged after failure of the innate system. This system produces specific responses to the type of pathogenic infections, and it has immunological memory – meaning information of specific pathogen is stored so that in future an enhanced response is conducted. A response is produced when the antigen of the pathogen binds to T cells or B cells, which identify and produce customized antibodies that help the breakdown of specific pathogens.
Mutations in the immune system can lead to immunodeficiency, autoimmunity and hypersensitivity. Immunodeficiency occurs when a part of the immune system is inactive or fails to respond, an example is Acquired Immunodeficiency Syndrome (AIDS). Autoimmunity is when the B and T cells cannot properly identify pathogens, and can lead to the immune system attacking the host body – example is Celiac disease. Hypersensitivity is excessive, side effect reactions that damage tissues in the body, an example is allergies.