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Chapter 34: Resistance of the Body to Infection. II.
Immunity and Allergy Innate Immunity
Guyton and Hall, Textbook of Medical Physiology, 12th edition
Innate Immunity
• Innate Immunity
a. Phagocytosis of bacteria and other invaders by wbcs and
cells of the tissue macrophage system
b. Destruction of swallowed organisms by stomach
acid and digestive enzymes
c. Resistance of the skin to invasion
d. Presence of antibacterial chemicals (i.e. lysozyme,
complement, NK cells, etc.)
Acquired (Adaptive) Immunity
• Basic Types
a. Humoral or B-cell Immunity
b. Cell-mediated or T-cell immunity
•
Initiation of the Responses- antigens
a. MW greater than 8000
b. Epitopes or antigenic determinants on surface
c. Generally protein or large polysaccharides
Lymphocytes
• T and B Lymphocytes
a. T lymphocytes migrate from the bone marrow to the
thymus where they mature and are responsible for
cell mediated immunity
b. B lymphocytes are preprocessed in the liver, then the bone
marrow and are responsible for antibody production
The “B” designation originated from the bursa of
Fabricius in the chicken.
Fig. 34.1 Formation of antibodies and sensitized lymphocytes from a lymph node in response to antigens
Lymphocytes (cont.)
• Preprocessing of the T Lymphocytes-occurs
shortly before or just after birth
a. In the thymus each T cell develops specificity against
one antigen
b. Continues until there are thousands of different T cells
with specific reactivities against 1000s of antigens
c. T cells then migrate to the secondary lymphoid tissues
d. T cells capable of reacting against “self-antigens” are
destroyed instead of being released
Lymphocytes (cont.)
• Preprocessing of the Lymphocytes
a. Instead of the whole cell developing reactivity against
the antigen, the B cells actively secrete antibodies that
are the reactive agents
b. Greater diversity than T cells: can form millions of
types of antibodies with different specific reactivities
•
T-Cells and B-Cell Antibodies React Highly Specifically
Against Specific Antigens-Role of Lymphocyte Clones
Lymphocyte Clones
Fig. 34.2
Lymphocyte Clones (cont.)
a. Millions of specific types of lymphocytes are stored in
the lymphoid tissues
b. Origin of the many clones of lymphocytes
c. Mechanism for activating a clone of lymphocytes
d. Role of macrophages
e. Role of the T cell in the activation of B cells
Humoral Immunity and the Antibodies
• Formation of Antibodies by Plasma Cells
• Formation of “Memory” Cells
• Difference Between Primary and Secondary Responses
Humoral Immunity and the Antibodies
Fig. 34.3 Primary and secondary antibody responses
Antibodies (cont.)
• Nature of Antibodies
a. Gamma globulins (immunoglobulins
b. MW between 170,000 and 970,000
c. Make up 20% of all the plasma proteins
d. Consist of heavy and light polypeptide chains
e. Have variable and constant regions
Antibodies (cont.)
Fig. 34.4 Structure of the typical IgG antibody
Antibodies (cont.)
• Specificity of Antibodies-each antibody is specific
for a particular antigen
Ka is the affinity constant and a measure of
how tightly the antibody binds to the antigen
Antibodies (cont.)
• Classes of Antibodies
Class
IgG
IgM
Structure
Location
Monomer
Blood,
Lymph,
Intestine
Pentamer
MW
170,000
Half-Life
In Serum
Function
23 days
Phagocytosis,
neutralization,
crosses
placenta
Blood,
Lymph, B
cell surface
970,000
5 days
Primary
response,
phagocytosis,
agglutination
IgA
Dimer
Secretions
405,000
6 days
Mucosal ab
IgD
Monomer
B cell
surface
175,000
3 days
Surface Ig on B
cells
IgE
Monomer
Cell bound
to mast
cells and
basophils
190,000
2 days
Allergic
Reactions,para
sitic reactions
Antibodies (cont.)
• Mechanism of Action of Antibodies (Direct)
a. Agglutination
b. Precipitation
c. Neutralization
d. Lysis
Antibodies (cont.)
• Mechanism of Action of Antibodies (Indirect)-the
Complement System
Fig. 34.6
Antibodies (cont.)
• Classic Pathway
a. Opsonization and phagocytosis
b. Lysis
c. Agglutination
d. Neutralization of viruses
e. Chemostaxis
f. Activation of mast cells and basophils
g. Inflammatory effects
Activated T Cells and Cell-Mediated Immunity
• Release of Activated T Cells From Lymphoid Tissue
and Formation of Memory Cells
• APCs, MHC Proteins, and Antigen Receptors on
T lymphocytes
Activated T Cells and CMI (cont.)
Fig. 34.7 Activation of T cells requires interaction of T cell receptors
with an antigen that is transported to the surface of the APC
by a MHC protein.
Types of T Cells
• Helper T Cells—Role in Overall Regulation of
Immunity
a. Production of lymphokines (i.e. interleukins
2,3,4,5,6 and gamma interferon)
b. Specific regulatory functions of the lymphokines
c. Stimulation of growth and proliferation of
cytotoxic T cells and suppressor T cells
d. Stimulation of B cell growth and differentiation
to form plasma cells and antibodies
Types of T Cells (cont.)
• Helper T Cells—Role in Overall Regulation of
Immunity (cont.)
e. Activation of the macrophage system
f. Feedback stimulatory effect on the helper
cells themselves
Types of T Cells (cont.)
Fig. 34.8 Regulation of the immune system
Types of T Cells (cont.)
• Cytotoxic T Cells are “Killer” Cells
Fig. 34.9 Direct destruction of an invading cell by sensitize T cytotoxic cells
Types of T Cells (cont.)
• Suppressor T Cells
a. Can suppress the functions of both T helper and
T cytotoxic cells
b. Regulatory cells—prevent excessive immune
reactions that might be damaging to the host
Tolerance
• Tolerance to One’s Own Tissues
• Results from Clone Selection During Preprocessing
• Failure Leads to Autoimmune Diseases
a.
b.
c.
d.
Rheumatic fever
Glomerulonephritis
Myasthenia gravis
Systemic lupus erythematosus (SLE)
Immunization
•
Active Immunity
a. Artificially acquired
b. Naturally acquired
•
Passive Immunity
a. Artificially acquired
b. Naturally acquired
Allergy and Hypersensitivity
• Type I Hypersensitivity (IgE antibody mediated)
a.
b.
c.
d.
Anaphylaxis
Urticaria
Hay fever
Mast cell involvement and histamine
• Type II Hypersensitivity (Cytotoxic reactions)
• Type III Hypersensitivity (Immune complex)
• Type IV Hypersensitivity (Delayed cell mediated)