immune system

Innate / Nonspecific Immunity

• Present at birth and provides a general, nonspecific defense.

• Responds relatively quickly and does not target one specific antigen.

Examples: species resistance, mechanical and chemical barriers, phagocytosis, inflammation, fever, interferons, and certain white blood cells.

Adaptive/ specific immunity

• Targets specific antigens and involves B and T lymphocytes.

• Develops after exposure to an antigen and produces memory cells.

• The initial adaptive response is slower, but later responses to the same antigen can be faster and stronger.

First line defense

Line of defense:

skin, mucous membranes, mechanical barriers, and chemical barriers prevent entry.

Second line

Line of defense:

phagocytosis, inflammation, fever, interferons, and natural killer cells respond after entry.

Third line of defense

Line of defense:

adaptive/specific immunity involving B cells, T cells, antibody-mediated immunity, and cell-mediated immunity.

Self tolerance

ability of the immune system to recognize normal body cells as self, attack foreign or abnormal cells, and avoid attacking the body's own normal cells.

Phagocytosis

• A nonspecific defense in which a cell engulfs and destroys microorganisms or other particles.

• associated with the inflammatory response and is NOT a major component of the third line of defense.

Simplified sequence: Microorganism is engulfed → trapped inside the phagocyte - lysosomal enzymes destroy it.

Phagocytosis

• Chemotaxis attracts WBCs toward chemicals released from damaged or infected tissue.

• Diapedesis allows WBCs to move through blood vessel walls.

• Chemotaxis and diapedesis help WBCs reach the problem; they do not destroy the microorganism.

• Important phagocytes include neutrophils, monocytes, and macrophages.

interferons

• Part of a nonspecific defense and are especially important against viral infections

• interfere with viral activity, inhibit viral replication, and help limit the spread/development of viral infection

• interferon → interferes with viruses

inflammation

• Nonspecific response to tissue injury or infection

• Blood flow increases, vessels become more permeable, and chemicals attract WBCs into that area

• Phagocytes help remove microorganisms and damaged material

• Redness, swelling, heat, pain

• Antibody formation is not part of the nonspecific inflammatory response. Antibodies belong to adaptive/specific immunity

fever

part of the body’s nonspecific defense

• Not always detrimental. A moderate increase in temp may slow down some microorganisms and support immune system activity

neutrophils

most numerous circulating WBCs, important phagocytes, often respond early to infection

monocytes

circulate in the blood and can leave the bloodstream to develop into macrophages

macrophages

large phagocytes; engulf foreign material and can help activate/ sensitize T cells

natural killer cells

Lymphocytes involved in nonspecific immunity and they attack certain abnormal or infected cells

antigens

a macromolecule that causes the immune system to make specific responses

antigenic determinant ~ epitope

The specific portion of an antigen recognized by the immune system

hapten

incomplete antigen

b cells

1. antibody-mediated (humoral) immunity

2. can become plasma cells

3. Plasma cells produce antibodies

4. can form memory B cells

T cells

1. Cell-mediated immunity

2. do not become plasma cells

3. Specialized T cells perform different immune functions

4. can form memory T cells

development of b and t cells

• b cells mature in the bone marrow

• Before activation, B cells may be called naive, virgin, or inactive B cells

• T cells mature in the thymus

• Developing T cells in the thymus are called thymocytes

• B CELLS DON’T HAVE TO BECOME THYMOCYTES

activation of B cells

• A B cell begins in an inactive or naive state

• When the appropriate antigen binds, the b cell becomes activated and may be referred to as an effector b cell

• Following activation and cloning, B cells can produce plasma cells and memory b cells

• naive B cell → antigen exposure/ activation → effector B cell → plasma cells + memory cells

• plasma secretes antibodies

• memory B cells remain and help produce a faster response if the antigen is encountered again

T cells

• Responsible for cell-mediated immunity

• Cloning can produce functional T cells and memory T cells

* Cloning does not produce plasma cells. Plasma cells develop from B cells

helper and suppressor/ regulatory t cells

• helper T cells stimulate and coordinate immune responses and can release cytokines that help activate other immune cells

• suppressor/regulatory t cells help decrease or regulate immune responses

• do not confuse helper t cells → stimulate/coordinate

• suppressor/regulatory T cells → suppress/regulate

cytokines

• They are chemical messengers released by immune cells

• allow immune cells to communicate and influence others

• Examples include certain interleukins and interferons

antibodies

Proteins involved in specific immunity. They are produced and secreted by plasma cells, which develop from activated B cells

antibody : igG

most abundant circulating antibody; about 75% of antibodies in blood; important in secondary responses

greatest amount

igM antibody

important antibody produced following initial contact with an antigen

made first

igA antibody

Commonly found in secretions such as tears and saliva

around in secretions

igE antibody

associated with allergic reactions

allergies

igD antibody

Function is less clearly understood

dont know as much

primary response

• occurs after first exposure

• takes time to develop

• igM is important early

• memory cells are formed

secondary response

• occurs after later exposure

• faster and stronger

• IgG is important

• Memory cells recognize the antigen quickly

active immunity

The person’s own immune system produces the response; it usually produces memory

passive immunity

The person receives antibodies produced by someone else; protection is more immediate but generally does not create long-term memory

active natural immunity

• your own immune system responds after natural exposure

• Example: immunity after having measles

active artificial immunity

Own immune system responds after medical exposure

example : vaccination

passive natural immunity

antibodies naturally transferred from another person

example: maternal antibodies transferred to baby

passive artificial immunity

Prepared antibodies are medically administered

example : injection of antibodies/immunoglobins

immune memory

• Memory cells remain after the initial immune response

• Later exposure to the same antigen can trigger a faster and stronger secondary response

allergies and histamines

• IgE is associated with allergic reactions

• Histamine contributes to swelling, redness, itching, and increased secretions

• Antihistamines reduce allergy symptoms by blocking or reducing the effects of histamine

transplant rejection and immunosuppression

• The immune system may recognize transplanted cells as foreign/ nonself and attack them

• Immunosuppressive medications decrease immune activity and can help prevent transplant rejection

HIV and AIDS

• HIV infected cells involved in immune function and can eventually result in severe immune deficiency

• A person can be infected with HIV for years before signs of AIDS become apparent

• Progression varies among individuals, making it difficult to predict exactly when AIDS will develop