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Immune system 2
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3. Three layers of defense
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Three layers of defense
The immune system protects the body with three layers of defense:
physical and chemical barriers, like the skin and chemicals produced by mucous membranes (tears, saliva, acids in the stomach and vagina, ear wax);
innate immune system;
adaptive immune system. 3
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4. Cells of the innate immune system
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Cells of the innate immune system
The innate immune system (non-specific immune system) consists of cells and chemical signals that have the ability to:
recognize pathogens through antigen receptors;
call other defense cells;
destroy pathogens and infected cells.
Cells of the innate immune system:
phagocytes (neutrophils, macrophages, dendritic cells), that engulf and kill pathogens;
natural killer cells that kill infected or cancer cells. 4
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5. Inflammation and fever
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Inflammation and fever
Inflammation is the immune system’s response to infection.
The release of chemical signals (cytokines and histamine) attracts phagocytes and other cells of the immune system to an infection site.
Cytokines induce fever which stimulates immune response and reduces the growth rate of many pathogens. 5
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6. Cells of the adaptive immune system /1
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Cells of the adaptive immune system /1
B lymphocytes are the cells involved in humoral immunity (mediated by antibodies). They are produced by bone marrow wherein they become mature.
They release antibodies in response to the presence of an antigen.
antibody Y Y Y Y Y Y Y Y Y
antigen Y Y Y Y Y Y Y Y Y
B lymphocyte
pathogen 6
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7. Cells of the adaptive immune system /2
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Cells of the adaptive immune system /2
T lymphocytes are the cells involved in cell-mediated immunity. They are produced by the bone marrow, but mature in the thymus.
They fight pathogens by destroying infected cells.
infected cell
pathogens
T lymphocyte 7
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Memory cells
During the first response against a pathogen, lymphocytes respond to the antigen and fight the pathogen.
In case of a second encounter with the same antigen, memory cells produced during the first response activate the secondary response which is faster and more intense. 8
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9. Plasma cells and antibodies
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Plasma cells and antibodies
Plasma cells are white blood cells that produce a large number of antibodies.
Each antibody has a unique structure which allows it to recognize a specific antigen. Antibodies can be released by B lymphocytes and freely move in the blood stream or they can attach to the B lymphocyte membrane. Y Y Y Y Y Y Y Y Y Y 9
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10. Immunization Long-term immunity against a pathogen can be obtained:
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Immunization
Long-term immunity against a pathogen can be obtained:
through previous exposure to the natural pathogen;
with immunization (vaccination), through the administration of a vaccine. Vaccines contain the attenuated – or harmless form – of a pathogen. 10
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11. Diseases of the immune system
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Diseases of the immune system
Autoimmune diseases occur when the immune system in not working properly by attacking its own structures and damaging tissues and organs. Type I diabetes is an autoimmune disease.
In immunodeficiency disorders, the immune system correctly recognizes pathogens, but the response is insufficient. AIDS is an acquired immunodeficiency, caused by the HIV virus.
Allergies are anomalous immune responses against harmless substances. 11
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