The immune response is how your body recognizes and defends itself against bacteria, viruses, and substances that appear foreign and harmful.
Innate immunity; Humoral immunity; Cellular immunity; Immunity; Inflammatory response; Acquired (adaptive) immunity
The immune system protects the body from potentially harmful substances by recognizing and responding to antigens. Antigens are molecules (usually proteins) on the surface of cells, viruses, fungi, or bacteria. Nonliving substances such as
Even your own body's cells have
Innate, or nonspecific, immunity is the defense system with which you were born. It protects you against all antigens. Innate immunity involves barriers that keep harmful materials from entering your body. These barriers form the first line of defense in the immune response. Examples of innate immunity include:
- Enzymes in tears and skin oils
- Mucus, which traps bacteria and small particles
Innate immunity also comes in a protein chemical form, called innate humoral immunity. Examples include the body's complement system and substances called interferon and interleukin-1 (which causes fever).
If an antigen gets past these barriers, it is attacked and destroyed by other parts of the immune system.
Acquired immunity is immunity that develops with exposure to various antigens. Your immune system builds a defense that is specific to that antigen.
Passive immunity is due to antibodies that are produced in a body other than your own. Infants have passive immunity because they are born with antibodies that are transferred through the placenta from their mother. These antibodies disappear between 6 and 12 months of age.
Passive immunization may also be due to injection of antiserum, which contains antibodies that are formed by another person or animal. It provides immediate protection against an antigen, but does not provide long-lasting protection. Immune serum globulin (given for hepatitis exposure) and
The immune system includes certain types of white blood cells. It also includes chemicals and proteins in the blood, such as antibodies, complement proteins, and interferon. Some of these directly attack foreign substances in the body, and others work together to help the immune system cells.
Lymphocytes are a type of white blood cell. There are B and T type lymphocytes.
- B cells produce
antibodies. Antibodies attach to a specific antigen and make it easier for the immune cells to destroy the antigen.
- T cells attack antigens directly and help control the immune response. They also release chemicals, known as cytokines, which control the entire immune response.
As lymphocytes develop, they normally learn to tell the difference between your own body tissues and substances that are not normally found in your body. Once B cells and T cells are formed, a few of those cells will multiply and provide "memory" for your immune system. This allows your immune system to respond faster and more efficiently the next time you are exposed to the same antigen, and in many cases will prevent you from getting sick. For example, a person who has had chickenpox or has been immunized against chickenpox is immune from getting chickenpox again.
The inflammatory response (inflammation) occurs when tissues are injured by bacteria, trauma, toxins, heat, or any other cause. The damaged cells release chemicals including histamine, bradykinin, and prostaglandins. These chemicals cause blood vessels to leak fluid into the tissues, causing
The chemicals also attract white blood cells called phagocytes that "eat" microorganisms and dead or damaged cells. This process is called phagocytosis. Phagocytes eventually die. Pus is formed from a collection of dead tissue, dead bacteria, and live and dead phagocytes.
IMMUNE SYSTEM DISORDERS AND ALLERGIES
Immune system disorders occur when the immune response is inappropriate, excessive, or lacking. Allergies involve an immune response to a substance that most people's bodies perceive as harmless.
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Vaccination (immunization) is a way to trigger the immune response. Small doses of an antigen, such as dead or weakened live viruses, are given to activate immune system "memory" (activated B cells and sensitized T cells). Memory allows your body to react quickly and efficiently to future exposures.
COMPLICATIONS DUE TO AN ALTERED IMMUNE RESPONSE
An efficient immune response protects against many diseases and disorders. An inefficient immune response allows diseases to develop. Inadequate, inappropriate, or excessive immune response causes immune system disorders.
Complications related to altered immune responses include:
- Autoimmune disorders
- Blood transfusion reaction
- Disease development
Graft versus host disease
- Immunodeficiency disorders
- Transplant rejection