The immune system refers to a collection of cells and proteins that function to protect the skin, respiratory passages, intestinal tract, and other areas from foreign antigens, such as microbes (organisms such as bacteria, fungi, and parasites), viruses, cancer cells, and toxins. The immune system can be simplistically viewed as having two “lines of defense”: innate immunity and adaptive immunity. Innate immunity represents the first line of defense to an intruding pathogen. It is an antigen-independent (non-specific) defense mechanism that is used by the host immediately or within hours of encountering an antigen. The innate immune response has no immunologic memory and, therefore, it is unable to recognize or “memorize” the same pathogen should the body be exposed to it in the future. Adaptive immunity, on the other hand, is antigen-dependent and antigen-specific and, therefore, involves a lag time between exposure to the antigen and maximal response. The hallmark of adaptive immunity is the capacity for memory which enables the host to mount a more rapid and efficient immune response upon subsequent exposure to the antigen. Innate and adaptive immunity are not mutually exclusive mechanisms of host defense, but rather are complementary, with defects in either system resulting in host vulnerability.
The immune system is a complex system of structures and processes that have evolved to protect us from disease. Molecular and cellular components make up the immune system. The function of these components is divided up into nonspecific mechanisms, those which are innate to an organism, and responsive responses, which are adaptive to specific pathogens. Fundamental or classical immunology involves studying the components that make up the innate and adaptive immune system.
Innate immunity is the first line of defense and is non-specific. That is, the responses are the same for all potential pathogens, no matter how different they may be. Innate immunity includes physical barriers (e.g. skin, saliva, a, etc) and cells (e.g. macrophages, neutrophils, basophils, mast cells, etc.). These components ‘are ready to go and protect an organism for the first few days of infection. In some cases, this is enough to clear the pathogen, but in other instances, the first defense becomes overwhelmed and the second line of defense kicks in.
Adaptive immunity is the second line of defense which involves building up the memory of encountered infections so can mount an enhanced response specific to the pathogen or foreign substance. Adaptive immunity involves antibodies, which generally target foreign pathogens roaming free in the bloodstream. Also involved are T cells, which are directed especially towards pathogens that have colonized cells
and can directly kill infected cells or help control the antibody response.
Immunology and infectious diseases is a specialty dealing with the body’s ability to response to infection.
Impaired or compromised immunity, auto immune disorders and multiple other conditions dealing with immunity are diagnosed and managed.