Immune System
Chapter 43
What you need to know!
• Several elements of an innate immune
response.
• The differences between B and T cells
relative to their activation and actions.
• How antigens are recognized by immune
system cells.
• The differences in humoral and cellmediated immunity.
• Why Helper T cells are central to immune
responses.
Organic, cellular, molecular componenets
• Lymphatic system: lymph ducts, lymph nodes, lymphatic
organs (thymus gland, spleen, and tonsils)
• White blood cells: B-cells, T-cells, macrophages, and
memory cells all mature from stem cells which originate
in the bone marrow
• Protein factors: antibodies and antigens
• Hormones: interferons and histamines
Antigen
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Protein or polysaccharide for cell recognition
Plasma membrane embedded surface protein
Antibody receptors (key-lock)
Very specific for each individual
About 20 in humans called major histocompatibility
complex (MHC)
• MHC are genetically coded
Antibody
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Immunogen
Antigen receptors
Free circling in blood or attached on B-cell surface
Several classes IgA, IgD, etc.
Quaternary protein made of 2 light, and 2 heavy chains
Antibody Structure
First Line of Defense (barriers/non-specific)
• External barriers (skin) with antimicrobial substances
(acidic pH)
• Mucus membranes lining the digestive, respiratory,
excretory, and female reproductive system which
constantly secrete mucus for the trapping and removal of
unwanted substances
• Cells are ciliated, cilia sway to keep mucus flow
outward
• Chemical substances such as gastric juice which kills
most bacteria and viruses (exceptions include Hepatitis
A)
Second Line of Defense
(internal/nonspecific)
I. Phagocytes are amoeboid white blood cells; there are
many different kinds:
• Neutrophils (60-70% of WBC): can leave the blood
stream to combat invaders; short life span (2 days)
• Monocytes (5% of WBC): develop into macrophages
• Macrophages: large, long-lasting destroyers, contain lots
of digestive enzymes for phagocytosis; permanent
residents of your alveoli, liver, and lymph nodes
• Eosinophils: fight internal parasites
• Natural Killer Cells: fight infected body cells (virus), and
precancerous cells
Second Line of Defense
(internal/nonspecific)
II. Inflammation: Injuries are invasion sites for microbes
which trigger histamine release which causes:
• Vasodilation (heat sensation)
• Higher capillary permeability (WBC and platelets)
• Release of prostaglandins (further inflammation)
• Platelets begin blood clotting process
• WBC fight invasion
• Microbes releasing toxins trigger release of pyrogens
(fever)
Third Line of Defense:
Specific Immune System
4 characteristics:
1. Specificity: focus on specific invader
2. Diversity: response to variety of invaders
3. Self/non-self recognition: antigen identification
4. Memory: cells keep information about previous infection
(memory cells)
Immunity includes:
• Active immunity: acquired through past infections or
vaccinations
• Natural passive immunity: mother passing antibodies
through placenta and breast milk
• Artificial passive immunity: injection of immunoglobulins in
response to venom (snake bite)
Humoral Immunity – Antibodies:
1.
2.
3.
4.
B-cells have an antibody-studded surface
Foreign antigens bind to antibodies on B-cells
Antigen-antibody complex stimulation
Stimulated B-cell will produce/release this specific
antibody as free floating antibody
5. Free floating antibodies will bind to all other antigens of
the same type
6. Macrophages recognize antibodies and phagocytosis
7. Specialized B-cells become memory cells to prevent
further attack from the same invader
Cell-mediated Immunity
1. T-cells have antigen recognition sites that are not
antibodies
2. When binding to a foreign antigen, the T-cell will
proliferate (reproduce) into helper T cells
3. Helper T cells identify pathogens to Killer T cells
4. Killer T cells use cytokines for apoptosis
Animation:
• http://www.youtube.com/watch?v=1tBOmG0QMbA