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Immune response

Show Alternative Names
Innate immunity
Humoral immunity
Cellular immunity
Immunity
Inflammatory response
Acquired (adaptive) immunity

The immune response is how your body recognizes and defends itself against bacteria, viruses, and substances that appear foreign and harmful.

Information

The immune system protects the body from possibly harmful substances by recognizing and responding to antigens. Antigens are substances (usually proteins) on the surface of cells, viruses, fungi, or bacteria. Nonliving substances such as toxins, chemicals, drugs, and foreign particles (such as a splinter) can also be antigens. The immune system recognizes and destroys, or tries to destroy, substances that contain antigens.

Your body's cells have proteins that are antigens. These include a group of antigens called HLA antigens. Your immune system learns to see these antigens as normal and usually does not react against them.

INNATE IMMUNITY

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:

  • Cough reflex
  • Enzymes in tears and skin oils
  • Mucus, which traps bacteria and small particles
  • Skin
  • Stomach acid

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

Acquired immunity is immunity that develops with exposure to various antigens. Your immune system builds a defense against that specific antigen.

PASSIVE IMMUNITY

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 ages 6 and 12 months.

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 tetanus antitoxin are examples of passive immunization.

BLOOD COMPONENTS

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 lymphocytes become cells that produce antibodies. Antibodies attach to a specific antigen and make it easier for the immune cells to destroy the antigen.
  • T lymphocytes 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. In many cases, it 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.

Immune response - Animation

Special white blood cells called lymphocytes play a key role in the immune system's response to foreign invaders. There are two main groups, both of which form in bone marrow. One group, called T-lymphocytes or T-cells, migrates to a gland called the thymus. Influenced by hormones, they mature there into several types of cells, including helper, killer, and suppressor cells. These different types work together to attack foreign invaders. They provide what's called cell-mediated immunity, which can become deficient in persons with HIV, the virus that causes AIDS. HIV attacks and destroys helper T cells. The other group of lymphocytes are called B-lymphocytes or B cells. They mature in the bone marrow and gain the ability to recognize specific foreign invaders. Mature B cells migrate through the body fluids to the lymph nodes, spleen, and blood. In Latin, body fluids were known as humors. So B-cells provide what's known as humoral immunity. B-cells and T-cells both circulate freely in blood and lymph, searching for foreign invaders.

INFLAMMATION

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 swelling. This helps isolate the foreign substance from further contact with body tissues.

The chemicals also attract white blood cells called phagocytes that "eat" germs 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.

Phagocytosis - Animation

These amoeba-like cells are a type of phagocyte called macrophages. They're scavenger cells that can form tentacles called pseudopods to surround and ingest foreign cells. Once swallowed, the cells are walled off and destroyed by a bag of digestive enzymes.

IMMUNE SYSTEM DISORDERS AND ALLERGIES

Immune system disorders occur when the immune response is directed against body tissue, is excessive, or is lacking. Allergies involve an immune response to a substance that most people's bodies perceive as harmless.

IMMUNIZATION

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.

Vaccines - Animation

Ouch! Vaccines help to give the body immunity from infections. Different vaccines work in different ways. Some vaccines inject fragments of a virus or bacteria called antigens into the body. Once in the blood, these antigens circulate among the blood cells, which include red blood cells and white blood cells. White blood cells, such as B and T cells, help fend off foreign invaders. When antigens invade tissue, they attract macrophages. These are scavenger cells that engulf the antigens. The macrophages then signal to T-cells that the antigens are invading. Killer T cells gather and attack the antigens. Then suppressor T cells stop the attack. After the vaccination, B-cells make defensive antibodies against the antigen. These antibodies help the cells remember this particular antigen, so that they can fight it off if the body is infected again.

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. Too much, too little, or the wrong immune response causes immune system disorders. An overactive immune response can lead to the development of autoimmune diseases, in which antibodies form against the body's own tissues.

Complications from altered immune responses include:

Review Date: 1/23/2022

Reviewed By

Stuart I. Henochowicz, MD, FACP, Clinical Professor of Medicine, Division of Allergy, Immunology, and Rheumatology, Georgetown University Medical School, Washington, DC. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

References

Abbas AK, Lichtman AH, Pillai S. Properties and overview of immune responses. In: Abbas AK, Lichtman AH, Pillai S, eds. Cellular and Molecular Immunology. 10th ed. Philadelphia, PA: Elsevier; 2022:chap 1.

Bankova L, Barrett N. Innate immunity. In: Burks AW, Holgate ST, O'Hehir RE, et al, eds. Middleton's Allergy: Principles and Practice. 9th ed. Philadelphia, PA: Elsevier; 2020:chap 1.

Firestein GS, Stanford SM. Mechanisms of inflammation and tissue repair. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 42.

Tuano KS, Chinen J. Adaptive immunity. In: Burks AW, Holgate ST, O'Hehir RE, et al, eds. Middleton's Allergy: Principles and Practice. 9th ed. Philadelphia, PA: Elsevier; 2020:chap 2.

Disclaimer

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. No warranty of any kind, either expressed or implied, is made as to the accuracy, reliability, timeliness, or correctness of any translations made by a third-party service of the information provided herein into any other language. © 1997- A.D.A.M., a business unit of Ebix, Inc. Any duplication or distribution of the information contained herein is strictly prohibited.

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Immune response

Immune response

Animation

Phagocytosis

Phagocytosis

Animation

Vaccines

Vaccines

Animation

Immune system structures - Illustration Thumbnail

Immune system structures

The immune system protects the body from potentially harmful substances. The inflammatory response (inflammation) is part of innate immunity. It occurs when tissues are injured by bacteria, trauma, toxins, heat or any other cause.

Illustration

Phagocytosis - Illustration Thumbnail

Phagocytosis

The chemicals also attract white blood cells that "eat" microorganisms and dead or damaged cells. The process where these white blood cells surround, engulf, and destroy foreign substances is called phagocytosis, and the cells are collectively referred to as phagocytes. Phagocytes eventually die. Pus is formed from a collection of dead tissue, dead bacteria, and live and dead phagocytes.

Illustration

 
Immune response

Immune response

Animation

Phagocytosis

Phagocytosis

Animation

Vaccines

Vaccines

Animation

 
Immune system structures - Illustration Thumbnail

Immune system structures

The immune system protects the body from potentially harmful substances. The inflammatory response (inflammation) is part of innate immunity. It occurs when tissues are injured by bacteria, trauma, toxins, heat or any other cause.

Illustration

Phagocytosis - Illustration Thumbnail

Phagocytosis

The chemicals also attract white blood cells that "eat" microorganisms and dead or damaged cells. The process where these white blood cells surround, engulf, and destroy foreign substances is called phagocytosis, and the cells are collectively referred to as phagocytes. Phagocytes eventually die. Pus is formed from a collection of dead tissue, dead bacteria, and live and dead phagocytes.

Illustration

 
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Immune response - Animation

Special white blood cells called lymphocytes play a key role in the immune system's response to foreign invaders. There are two main groups, both of which form in bone marrow.

One group, called T-lymphocytes or T-cells, migrates to a gland called the thymus.

Influenced by hormones, they mature there into several types of cells, including helper, killer, and suppressor cells. These different types work together to attack foreign invaders. They provide what's called cell-mediated immunity, which can become deficient in persons with HIV, the virus that causes AIDS. HIV attacks and destroys helper T cells.

The other group of lymphocytes are called B-lymphocytes or B cells. They mature in the bone marrow and gain the ability to recognize specific foreign invaders.

Mature B cells migrate through the body fluids to the lymph nodes, spleen, and blood. In Latin, body fluids were known as humors. So B-cells provide what's known as humoral immunity. B-cells and T-cells both circulate freely in blood and lymph, searching for foreign invaders.

 

Phagocytosis - Animation

These amoeba-like cells are a type of phagocyte called macrophages. They're scavenger cells that can form tentacles called pseudopods to surround and ingest foreign cells.

Once swallowed, the cells are walled off and destroyed by a bag of digestive enzymes.

 

Vaccines - Animation

Ouch!

Vaccines help to give the body immunity from infections. Different vaccines work in different ways. Some vaccines inject fragments of a virus or bacteria called antigens into the body. Once in the blood, these antigens circulate among the blood cells, which include red blood cells and white blood cells. White blood cells, such as B and T cells, help fend off foreign invaders.

When antigens invade tissue, they attract macrophages. These are scavenger cells that engulf the antigens. The macrophages then signal to T-cells that the antigens are invading. Killer T cells gather and attack the antigens. Then suppressor T cells stop the attack.

After the vaccination, B-cells make defensive antibodies against the antigen. These antibodies help the cells remember this particular antigen, so that they can fight it off if the body is infected again.

 

Immune response - Animation

Special white blood cells called lymphocytes play a key role in the immune system's response to foreign invaders. There are two main groups, both of which form in bone marrow.

One group, called T-lymphocytes or T-cells, migrates to a gland called the thymus.

Influenced by hormones, they mature there into several types of cells, including helper, killer, and suppressor cells. These different types work together to attack foreign invaders. They provide what's called cell-mediated immunity, which can become deficient in persons with HIV, the virus that causes AIDS. HIV attacks and destroys helper T cells.

The other group of lymphocytes are called B-lymphocytes or B cells. They mature in the bone marrow and gain the ability to recognize specific foreign invaders.

Mature B cells migrate through the body fluids to the lymph nodes, spleen, and blood. In Latin, body fluids were known as humors. So B-cells provide what's known as humoral immunity. B-cells and T-cells both circulate freely in blood and lymph, searching for foreign invaders.

 

Phagocytosis - Animation

These amoeba-like cells are a type of phagocyte called macrophages. They're scavenger cells that can form tentacles called pseudopods to surround and ingest foreign cells.

Once swallowed, the cells are walled off and destroyed by a bag of digestive enzymes.

 

Vaccines - Animation

Ouch!

Vaccines help to give the body immunity from infections. Different vaccines work in different ways. Some vaccines inject fragments of a virus or bacteria called antigens into the body. Once in the blood, these antigens circulate among the blood cells, which include red blood cells and white blood cells. White blood cells, such as B and T cells, help fend off foreign invaders.

When antigens invade tissue, they attract macrophages. These are scavenger cells that engulf the antigens. The macrophages then signal to T-cells that the antigens are invading. Killer T cells gather and attack the antigens. Then suppressor T cells stop the attack.

After the vaccination, B-cells make defensive antibodies against the antigen. These antibodies help the cells remember this particular antigen, so that they can fight it off if the body is infected again.

 
 
 
 

 

 
 
 
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