Microbiology – Online Lecture Notes
Immune System
I. 2 Types of Immunity
A. Innate Immunity
B. Adaptive (Acquired) Immunity
II. Innate Immunity
A. Present at birth
B. 1st Line of Defense
1. Skin
2. Mucous membranes (respiratory, urogenital, digestive)
3. Normal flora
C. 2nd Line of Defense
1. Phagocytes
a. Neutrophils – 1st to infected area
b. Eosinophils – worm infections
c. Macrophages – large aggressive phagocytes
d. Dendritic cells
1) Epidermis, mucous membranes, lymph nodes
2. Natural killer cells
a. Type of lymphocyte that kills our cells that have abnormal surface
proteins, i.e. infected cells (virus), cancer cells
3. Inflammation
4. Fever
5. Complement – “complements the actions of antibodies”
a. Group of 30 proteins produced by the liver that aids in the destruction of
microbes via cytolysis, as well as stimulating inflammation and phagocytosis.
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White Blood Cells There are 5 types of White Blood Cells (WBCs) 1. Monocytes 2. Neutrophils 3. Lymphocytes 4. Basophils 5. Eosinophils
During an infection *Neutrophils and monocytes migrate to the infected area (chemotaxis), then leave the blood and enter the tissue. Monocytes differentiate into macrophages.
*Neutrophils increase in number and are the first to the infected site; followed by an increase in monocyte proliferation and activity.
*Leukocytosis – increase in WBCs during infection |
D. Begins when our defensive cells (macrophages and dendritic cells) detect an invader
E. Toll-like receptors (TRL’s)
1. Found on the membranes of our defensive cells; bind to PAMP’s
F. Pathogen-associated molecular patterns (PAMPs)
1. The part of a pathogen that binds to the TRLs of our defensive cells
2. Lipopolysaccharides (LPS) of gram-bacteria, peptidoglycan of gram+ cell
walls, bacterial DNA, RNA, and DNA of viruses
G. TRL’s encounter and bind to PAMP’s
1. Triggers our defensive cells to produce Cytokines
H. Cytokines
1. Proteins that regulate the immune response
2. Attract macrophages, dendritic cells, and other phagocytes
3. Stimulates inflammation (TNF-α, tumor necrosis factor-alpha)
4. Fever (interleukin-1 and TNF-α)
II. Adaptive (Acquired) Immunity
A. Specific response to specific microbe
B. Acquired only through exposure
C. Has memory
D. Two Arms of Adaptive Immunity
1. Cellular Immunity
a. B Lymphocytes and T lymphocytes (a.k.a. B cells and T cells)
2. Humoral Immunity
b. Antibody production i.e. “the immune response”
E. Antigens
1. Proteins or polysaccharides
2. Found on capsules, cell walls, flagella, toxins, virus coats, etc
3. Non-microbial antigens include pollen, egg whites, tissue from another person, etc
4. Antigenic determinants (epitopes) – part of antigen we recognize as foreign
a. These are what antibodies bind to
b. Binding is based on a specific shape
F. Antibodies (a.k.a. immunoglobulins, Igs)
1. Proteins produced by plasma cells (plasma cells rise from B-cells)
2. 5 Classes
a. IgG
1) Most common in blood serum
2) Cross placenta to give fetus passive immunity
3) Activate complement (complement fixation)
4) Protect against bacteria, viruses, toxins
5) Small; can pass out of capillaries into tissue
b. IgA
1) Secretions – mucus, saliva, tears, breast milk (colostrum)
2) Most common throughout the body
c. IgM
1) 1st antibodies produced in infection
2) Large; results in clumping of bacteria and viruses
3) Complement fixation
4) Surface of B cells
d. IgE
1) Allergic reactions
2) Anchors to mast cells and basophils (release of histamine)
e. IgD
1) Surface of B cells
G. Humoral Immunity – “Production of Antibodies”
1. B cells have specific Igs on cell membrane
a. 100,000 identical Igs on same cell membrane
1) All bind same antigen
b. Mainly IgD and IgM
2. When specific antigen binds to specific immunoglobulin on a B cell, it activates that B lymphocyte
3. An activated B lymphocyte proliferates and produces
a. Plasma cells
1) Produce antibodies in 1° Immune Response
2) 1st type produced are IgM’s, then other classes are produced by same
plasma cell such as IgG and IgA
b. Memory cells
1) Long lived B-cells
2) Provides long term immunity
3) 2° Immune Response
a. If ever exposed to same antigen these cells will undergo clonal
selection; antibodies are produced faster and longer and bind tighter
b. Fights off invading antigen much better
4. Antigen-Antibody Complex
a. Antibody binds to antigen on specific epitope (antigenic determinant)
b. Antibodies don’t destroy antigens directly; they mark them for destruction
1) Complement proteins – destroy antigens
2) Opsonization – enhance phagocytosis
3) Mark them for NK cells, eosinophils, macrophages
4) Blocks attachment of viruses and toxins
H. Cellular Immunity – T cells
1. Combat intracellular bacteria/viruses, also cancer cells
2. T cells have specific receptors on their cell membranes
3. T cells are produces in red bone marrow; mature in thymus
4. Types of T cells
a. T helper cells (CD4 T cells)
1) Help B cells with humoral response (antibody production)
b. T cytotoxic cells (CD8 T cells)
1) Become cytotoxic T lymphocytes that can attack abnormal cells, i.e.
infected w/ virus and cancer cells
2) Different from NK cells because they need to be stimulated by a
specific antigen
c. T regulatory cells
1) Suppress immune function
2) Prevent autoimmunity
I. Immunological Memory
1. Antibody titer – amount of antibodies in serum
2. After 1st exposure to antigen (1° Immune Response)
a. No detectable antibodies for 4-7 days
b. Then slow rise in IgM’s followed by peak of IgG in 10-17 days
3. In subsequent exposure, the 2° Immune Response is much stronger
a. Immunity from memory cells that were made during 1° response
J. Types of Adaptive (Acquired Immunity)
1. Naturally Acquired Active Immunity
a. Actual exposure to antigen
b. Go through 1° Immune Response and produce memory cells
2. Naturally Acquired Passive Immunity
a. Transfer of antibodies from mother to child
1) Across placenta
2) Breast milk (colostrum)
3. Artificially Acquired Active Immunity
a. Vaccination (immunization)
b. Get weakened antigen
1) flu, measles, mumps, hepatitis
c. Go through 1° Immune Response and produce memory cells
4. Artificially Acquired Passive Immunity
a. Get injection of antibodies
b. Used to treat tetanus, botulism, rabies
