Chapter 8
The Immune
System
The immune system
•
Two general classifications
1. Non-specific immune system
2. Specific immune system
Visit the Immune System at www.niaid.nih.gov/final/immun/immun.htm
Cells of the immune system
The components
of non-specific immunity
• External mechanisms
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Skin
Digestive tract
Respiratory tract
Urinary tract
• Internal mechanisms
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Visit The Anatomy of the Immune System at
www-micro.msb.le.ac.uk/MBchB/2b.html
Phagocytic cells
NK cells
Complement proteins
Interferons
Phagocytosis
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Process by which unwanted particles
are engulfed and destroyed by
digestive enzymes
Two major groups of cells are
involved:
1. Neutrophils
2. Mononuclear phagocytes, which include:
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Monocytes
Macrophages
Tissue-specific phagocytes
Phagocytosis by a
neutrophil or macrophage
Natural killer (NK) cells
• Non-T and non-B lymphocytes thought
to be involved with immune surveillance
against cancer
• Method by which NK cells destroy virally
infected and tumor cells is unknown
Complement proteins
• System has nine protein components (C1
through C9)
• Exist in inactive state in blood and other fluids
• Destroy cells that have been marked for
elimination by antibodies
• Activation of the system occurs when
antibodies bind with antigens on the invading
cells
• Series of events follow that results in water
entering the cells and causing them to burst
Interferons
• Polypeptides that interfere with ability of
viruses to replicate
• Produced by cells infected with viruses; act
on neighboring cells to prevent infection
• Mechanics of the action are
– Direct: produces cellular enzymes that prevent
viral protein synthesis and destruction of viral
messenger RNA
– Indirect: stimulates NK and killer T cell activity
and antibody production in plasma cells
The two classifications of the
specific immune mechanisms
1. Humoral
2. Cell-mediated
Specific immune mechanisms
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Target antigen molecules
Antigen molecules exhibit two
characteristics
1. They stimulate antibody production
2. They combine with the specific antibody
The four components
of humoral immunity
1.
2.
3.
4.
B cells
Plasma cells
Antibodies
Memory B cells
The components
of cell-mediated immunity
• T cells, which give rise to:
– Killer T cells
– Helper T cells
– Suppressor T cells
– Memory T cells
B Cells
– Respond to antigens presented by
macrophages
– After exposure, divide into
• Plasma cells—secrete antibodies
specific to the antigen
• Memory B cells—remember a previous
invader and eliminate them
Role of B cells in humoral immunity
Antibodies
• Glycoproteins produced and
secreted by plasma cells
• Antibody itself does not directly
destroy cells but activates nonspecific immune mechanisms
For more information, visit Antibody Production at
www.cellsalive.com/antibody.htm
The T cells
• Killer T cells
– Must be near or in contact with the cell
targeted for destruction
– Produce lymphotoxins
– Release interferons and substances that
enhance phagocytosis
• Helper T cells
– Stimulate cytotoxic action of killer T cells
– Increase antibody production by plasma cells
The T cells (cont.)
• Suppressor T cells
– Regulate action of killer T cells and
development of B cells into plasma cells
– Keep immune defense from exceeding
limits necessary to destroy invading
organism
• Memory T cells
– Recognize an antigen from previous
exposure
Role of T cells in cellular immunity
Exercise alters several components
of the immune function, including
• Exercise results in leukocytosis
• Exercise results in lymphocytosis
• Exercise may increase interferon levels,
but the significance is unknown
HIV positive individuals and exercise
• Exercise does not exacerbate the progression of
HIV and may slow it.
• Exercise can help HIV-infected individuals
maintain health.
• Moderate aerobic exercise can increase helper T
cell and NK cell counts.
• Resistance training can help to maintain or
increase muscle mass and so diminish the weight
loss characteristic of stages 2 and 3 of HIV
infection.
For more information, visit Comprehensive AIDS and HIV Information
www.thebody.com
How to minimize the
risk of becoming ill
1. Allow sufficient time between training sessions for
recovery.
2. Avoid extremely long training sessions
3. Use periodization of training
4. Avoid training monotony by ensuring variation in
training load
5. When increasing the training load, do so on hard
days. Don’t eliminate recovery days
6. When recovering from overtraining or illness, begin
with light training and increase gradually.
7. Monitor and record mood, feelings of fatigue, and
muscle soreness; decrease the training load if the
session seems harder than usual.
How to minimize the
risk of illness (cont.)
8.
9.
10.
11.
Keep other stresses to a minimum.
Get regular and adequate sleep
Get more rest after travel across time zones
Pay attention to diet and make sure it is wellbalanced
12. Ensure adequate total dietary intake
13. Consider drinking carbohydrate sports drinks
before, during and after prolonged workouts
14. Consider vaccination.
Guidelines for training and
competition during an infection
– Exercise tolerance may be reduced during infection
– Exercising with an infection may increase the
duration of the illness
– Iron supplements should be avoided to limit
bacterial infection
– Training should be stopped if fever or systemic
symptoms are present
– Training should be resumed gradually
– Team members with infection should be isolated as
much as possible from the rest of the team