4 Basic Principles of Immunology
I.
Natural or Nonspecific Immunity
A. Antimicrobial Agents
B. Phagocytic Cells
C. Nonphagocytic Cells
D. Natural Killer Cells
E. Inflammation and Fever
II.
Acquired or Adaptive Immunity
A. Lymphocytes: 1. T cells
2. B cells
B. Major Histocompatibility Complex
C. Antibodies
III. Overview of Cell- and Antibody-Mediated Immune Responses
IV. Vaccines
A. Cause for Concern? New Vaccines for the Developing World?
V.
Immune System Disorders
A. Hypersensitivity
1. Allergies
2. Autoimmune Disorders
3. Immunodeficiencies - HIV and AIDS
VI. Monoclonal Antibodies
A. Biotech Revolution: Future of Monoclonal Antibody Production
VII. Tools of Immunology: A. Western Blotting
B. Fluorescent Antibody Technique
C. Enzyme-Linked Immunosorbent Assay
I.
Natural or Nonspecific Immunity
A. Rapid way for the body to fight off organisms before the specific mechanisms of
acquired immunity are activated (Figure 4.1, Table 4.1).
B.
Physical barriers are present, such as:
1.
2.
3.
4.
5.
6.
Skin and mucous membranes, which block entry of pathogens.
Sweat gland and tear duct secretions that contain lysozyme.
Blinking bathes eyes in tears that wash away pathogens.
Perspiration is acidic and prevents growth of microorganisms.
Stomach acid and other digestive enzymes.
Cilia in the respiratory tract.
C.
Antimicrobial Agents
1.
Act to deter or destroy microorganisms. Examples include:
2.
Interferon (Figure 4.2):
a) Called “cytokines” and serve as signals during the immune response.
b) Many different types generated, but mostly act against viruses.
c) Activates a series of reactions that trigger the synthesis of antiviral proteins (AVPs)
that affect the assembly of virus particles within the cell.
3.
Interleukins:
a) Produced by cells of the immune system and regulate interactions of immune cells
with other body cells.
4.
Lactoferrin and transferrin:
a) Bind and sequester the element iron to reduce its cellular amounts.
b) Inhibits bacterial growth because iron is needed for bacterial growth.
c) Transferrin is in blood, and lactoferrin is in milk, saliva, mucus, and tears.
5.
Complement (Figure 4.3):
a) A family of more than twenty proteins in blood serum.
b) Complement actions of other components of the immune system in the immune
response.
c) Activated by a complex series of reactions, working in four ways:
(1) They can form a coating on the pathogen surface so that phagocytes
(macrophages and neutrophils) can engulf easily.
(2) Lyse the cell wall of microorganisms.
(3) Release substances like histamine that increase inflammation, causing
increased capillary permeability and dilated blood vessels.
(4) They can attract lymphocytes (white blood cells) to an infection site.
D. Phagocytic Cells
1.
These are cells that destroy pathogens if they cross the physical barriers.
2.
Contain many enzymes for digestion such as lysozymes, proteases, nucleases, and lipases.
They also produce toxic substances such as hydrogen peroxide.
3.
Two types of phagocytes (Figure 4.4 & 4.5):
a)
Stationary phagocytes (macrophages):
(1) Large cells made in the bone marrow that live in two phases: a mobile phase in
the blood when they are called monocytes, and a stationary phase where they are
called macrophages.
(2) Engulf and consume bacteria, cancer cells, and virus-infected cells.
b)
Wandering phagocytes (leukocytes):
(1) Circulate in the blood, and are two types:
(a) Neutrophils (Fig 4.6)—best on bacteria, not used in sustained
responses, increase in response to infection, involved in
inflammation.
(b) Monocytes—the mobile phase of the macrophage.
E.
Nonphagocytic Cells
1.
a)
b)
c)
Three types:
Basophils—involved in inflammation and allergies.
Eosinophils—somewhat phagocytic and active against parasitic worms.
Lymphocytes—large cells that respond to specific organisms and are involved in acquired
immunity. Include B cells and T cells.
F.
Natural Killer (NK) Cells
1.
2.
3.
Non-phagocytic cells that attach to cell surfaces and produce enzymes that destroy cells
infected with viruses or microorganisms, even cancer cells.
They don’t attack the pathogen, but cells infected with the pathogen.
Cells are coated in antibodies and are then recognized and killed by NK cells.
G.
Inflammation and Fever (Figure 4.7)
1.
2.
Nonspecific responses to infection by microorganisms and tissue damage.
Inflammation:
a) Chemicals such as prostaglandins (cause vasodilation) and histamine (causes
increased capillary permeability) are produced.
b) Characterized by swelling (by an influx of cells and plasma fluid), pain (caused by
swelling), warmth, and redness (by increased blood flow).
c) Blood cells, dead cells, and microorganisms are trapped, and phagocytes destroy
and remove invading microorganisms.
Fever:
a) Induced by substances produced by pathogens, and causes body temperature to
rise.
b) Kills pathogens, increases inflammation, and stimulates phagocyte activity.
c) Also reduces amount of iron in blood to inhibit bacterial growth.
3.
II.
Acquired or Adaptive Immunity (Figure 4.8)
A.
Recognizes foreign invaders and responds to the invader, called
an “antigen” (Figure 4.9).
B. Can also recognize the body as self and the tissues of others as
non-self.
C. Antigens can be protein, glycoprotein, polysaccharides, and
nucleic acids, and small parts of the antigen can trigger a response
(called the “antigenic determinant”).
D. Based on the complex interactions of different types of cells and
other components (Figure 4.10). There are two types:
1. Cell-mediated—mediated by cells called “T lmphocytes”
(T cells) (Figure 4.11)
2. Antibody-mediated—mediated by cells called “B
lymphocytes” (B cells) (Figure 4.12).
E. Lymphocytes are circulated in the blood (by blood vessels) and
lymphatic system (by lymphatic vessels) and in organs such as the
spleen, tonsils, and thymus gland.
F.
Lymphocytes
1.
2.
3.
4.
Have specific receptors on the surface to recognize antigenic determinants.
The primary cells are T cells, B cells, and NK cells.
T cells (Figs 4.13, 4.14, 4.15):
a) 60% of all lymphocytes; they develop in the bone marrow and mature in the thymus gland.
b) Four major types:
(1) CD8—cytotoxic T cells. Directly kills cancer, infected, or foreign cells.
(2) CD4—helper T cells. Secretes growth factor that stimulates B cell reproduction,
antibody production, and activity of CD 8 T cells.
Two types—T helper 1 (TH1) is involved in cell-mediated immunity, while T helper 2
(TH2) is involved in antibody-mediated immunity.
(3) Suppressor—inhibit immune reactions by decreasing the activity and division
rates of B and T cells.
(4) Memory—waits reintroduction of antigen, when they quickly divide and
differentiate into CD8, CD4, and suppressor T cells.
c) Contain the T cell receptor, a glycoprotein that recognizes and binds to antigens on infected
cells or on cells that present the antigen, called “antigen-presenting cells” (APCs), of which
macrophage is an example.
B cells (Fig 4.16):
a) Develop and mature in the bone marrow. b) Three types of B cells, based on function:
(1) Naïve B cells—not yet been exposed to an antigen, contain about 100,000
antibody molecules on the cell surface. They move into the lymph nodes. When exposed
to an antigen, they become plasma cells, producing one specific antibody.
(2) Plasma cells—makes antibodies specific for antigen it was exposed to. Also
called effector B cells.
(3) Memory B cells—do not die like plasma cells; produces small amounts of antibodies
waiting for reintroduction of the antigen. They then divide quickly and differentiate into
plasma cells.
G. Major Histocompatibility Complex (Figure 4.17)
1.
Body cell antigens that identify the cells of the body as self.
2.
APCs present antigens as complexes with MHC, activating T and B cells.
3.
Three classes of proteins make up the MHC:
a)
b)
c)
MHC class I—on most cells, involved in self-recognition. Can bind to
antigens.
MHC class II—found on macrophages, B cells, dendritic cells, and
some T cells. Regulate interactions among APCs, B cells, and T cells.
Bind to antigens that APCs have engulfed and destroyed.
MHC class III—make up some of the proteins in the complement
system.
H.
Antibodies (Figure 4.20)
1.
2.
3.
4.
5.
Made of four polypeptide chains:
a) Two heavy chains and two light chains.
b) Each chain has a constant (C) region and a variable (V) region, which are also
called “Fab fragments” and can change during the differentiation and
activation of B cells.
Bind to antigens and trigger several responses:
a) Inactivation of a pathogen to prevent a cell from infection.
b) Activation of phagocytes that ingest pathogens.
c) Activation of complement proteins that destroy the pathogen.
d) The constant region, called the “Fc region,” bind sto Fc receptors on
phagocytes.
Classified based on the amino acid sequences on the C region of the heavy chain:
a) IgA—prevents pathogens from binding to epithelial surfaces. Found in
mucus, tears, saliva, and breast milk.
b) IgD—on the surface of B cells, activates B cells after they attach to antigens.
c)
IgE—binds to mast cells, causing them to release histamine, causing
inflammatory responses. Also involved in parasitic worm infections.
d) IgG—found in plasma and involved in long-term immunity. Helps provide
immunity in newborns (called “passive immunity”).
e) IgM—produced during the first encounter with an antigen and are found on
the surface of B cells.
Have a large diversity, generated during the differentiation and maturation of B
cells. DNA that codes for the constant and variable regions of the heavy and light
chains of the antibody are randomly arranged to form a unique antibody. Can
possibly create up to 100 million different antibody genes (Figure 4.22).
Overall, the specific and nonspecific immune responses work together to provide
immunity, as seen in Table 4.9.
III.
Overview of Cell and Antibody-Mediated Immune Responses
A.
During the cell-mediated immune response (Figure 4.23):
1.
Virus invades cells of the body.
2.
Foreign antigens combine with MHC and form foreign antigen-MHC
(class I) complex that is displayed on surfaces of antigen-presenting cells.
3.
Specific T cells are activated by foreign antigen-MHC complex.
4.
T-cell clone produced by cell division—some become cytotoxic T cells.
5.
Cytotoxic T cells migrate to infection site.
6.
Cytotoxic cells secrete proteins that destroy target cells—those infected by
virus.
7.
Helper T cells secrete substances that attract macrophages and other cells
to help fight infection.
B. During the antibody-mediated immune response (Figure 4.18):
1.
A pathogen with a foreign antigen penetrates body.
2.
Antigen-presenting cells (APCs) (for example, macrophages) phagocytize (ingest) the
pathogen and display the antigen on their surface so they are recognized by the
immune system.
The foreign antigen along with the MHC (antigen-MHC complex) is displayed on the
surface of the phagocytes.
3.
4.
Helper T cells bind with foreign antigen and become activated.
5.
B cells display the antigen of the infecting microorganism to activated helper T cells.
6.
New B cells are produced through cell division.
7.
B cells differentiate and become plasma cells.
8.
Plasma cells secrete antibodies.
9.
Antibodies attach to the pathogen.
10. Antibody-pathogen complexes trigger the destruction of the pathogen by other cells and
chemicals.
IV. Vaccines
A. Provides active immunity (the full immune response) to a pathogen, which is
usually provided through exposure to a pathogen (naturally or artificially by
vaccination). Table 4.10 lists some current vaccines.
1. Protection by a vaccine occurs in several ways:
a)
b)
c)
d)
e)
Weakened virus (live, attenuated vaccine) that do not cause disease.
Killed pathogens (inactivated vaccines). They cause an immune response
because the antigens are still present to cause an immune response.
Examples are the typhoid, whooping cough, and rabies vaccines.
The toxin isolated from a pathogen can be modified to eliminate the
toxic properties of the substance; however, it still remains antigenic
(toxoid vaccine). The tetanus vaccine is an example.
Subunit vaccines are used to provide extra shield against side effects.
Specific antigens from the pathogen are used in the vaccine. For
example, one coat protein from a virus will produce an immune
response. Do not stimulate the immune system as strongly as other
vaccines, but recombinant DNA technology is increasing their ability to
provide an immune response (mutations to increase antigenecity and
the response of the immune system).
Different antigens can be mixed to create a stronger immune response
and, thus, better protect the individual. These are called “multivalent
vaccines.”
B.
Potential other developments in vaccine technology include:
1. Small synthetic peptides that elicit an immune response but lack parts that
cause side effects.
2. Nucleic acid (DNA or RNA) vaccines made from the pathogens genome.
DNA is injected in the patient, gets incorporated in their genome, then
expressed to produce a polypeptide that can elicit an immune response.
DNA vaccines for HIV are in clinical trials).
3. Therapeutic vaccines for cancer cells which have altered anitgens onn their
surface that can hide from the immune system. Engineered antigens
specific for binding to tumor cells can elicit a strong immune.
4. Production of edible vaccines in plants such as potato, tomato, and
banana. Such vaccines don’t require refrigeration and are intended for the
developing world.
C.
Cause for Concern? New Vaccines for the Developing World?
1.
Vaccines that are currently developed will be of great benefit in the
United States, but what about the developing world?
2.
Will vaccines for diseases in the developing world be developed? Will
those vaccines be tailored to places where refrigeration is not adequate?
Will those vaccines be distributed to those who need it quickly?
V.
Immune System Disorders
There are occasions where the immune system is overactive and attacks
molecules and cells produced by the body.
A.
Hypersensitivity.
1. Allergies.
a) Occur in response to food, insect stings, antibiotics, and plant oils
(e.g. poison ivy).
b) Antigens that cause the allergic response are called “allergens.”
c) Two types of immune responses to allergens:
(1) Cell-mediated allergy—mediated by T cells and macrophages in
response to contact with plant oils, chemicals, and latex, which
bind to cell membrane proteins in cells that make up the skin.
Delayed response.
(2) Antibody-mediated allergy—induces hay fever, asthma, and
reactions to insect stings. IgE is made and binds to basophils
and mast cells, causing the release of histamine. Treated with
antihistamine drugs, steroid hormones, or desensitization
treatments.
2. Autoimmune Disorders
a)
b)
When the immune system malfunctions and attacks the body’s own cells.
Two types of autoimmune disorders:
(1)
Cytotoxic hypersensitivity—the immune system attacks itself. IgM
or IgG antibodies mistake the body’s own cells for invaders, bind to
the cells, and the cells are destroyed by phagocytes or killer cells.
Grave’s disease and Hashimoto’s thyroiditis are examples.
(2)
Immune-complex hypersensitivity—circulating molecules are
attacked. Antibodies attach to antigens in the blood, and the
antigens are then either removed from the blood or lodge in tissue,
causing an inflammatory response. Lupus is an example.
3.
Immunodeficiencies
a)
b)
Occurs when the immune system is unable to function at a proper level, and is
defined by what is causing the deficiency (Table 4.12).
HIV and AIDS.
(1) Caused by a retrovirus (Figure 4.24) that binds to and attacks CD4 T cells.
(2) The virus enters the cell and releases its RNA genome and the enzyme reverse
transcriptase, which makes DNA from the RNA (Figure 4.25).
(3) The DNA integrates into the host genome and can lie dormant for years.
(4) The virus becomes active and reproduces, eventually killing CD4 T cells and
weakening the immune response.
(5) The immune system cannot attack HIV because HIV cannot be recognized
inside of cells, the coat proteins of the virus mutate rapidly to allow HIV to
evade the immune system, and other properties described in Table 4.13.
VI. Monoclonal Antibodies
A.
Antibodies are used in biotechnology to detect diseases, as therapeutic agents, and
tools in research. They can be produced in the laboratory against specific antigens,
usually by a laboratory animal like a mouse.
B.
Antibodies can be:
1. Polyclonal—a mixture of different antibodies having different specificities to the
molecule of interest.
2.
Monoclonal—a mixture of one antibody that is specific for only one antigen.
C.
Monoclonal antibodies (MAbs)are produced in this fashion:
1.
Mice are injected with the antigen, whch elicits an immune response in the mice.
2. The mouse’s spleen is removed, and B cells harvested.
3.
The B cells are fused with cancer cells (usually a myeloma cell that would
become a B cell) that will divide indefinitely and also mass-produce antibodies.
The fused cell is now called a hybridoma.
4.
The cells are separated and screened for production of the proper antibody.
5.
The correct cell is obtained and its antibodies used.
D.
Monoclonal antibodies have many uses in biotechnology, such as in
immunoassays that detect molecules; therapeutic treatments such as possibly
aiding in cancer treatments; and in protein purification (called “affinity
purification”) that can remove one protein from a mixture.
E.
Biotech Revolution: Future of Monoclonal Antibody Production
VII.
Tools of Immunology
A.
Western Blotting (Figure 4.26).
1. A technique used to detect a specific protein that is mixed
with other proteins.
2.
This is performed in a manner similar to Southern blotting.
3.
The Western blot is performed in the following steps:
a) Sodium dodecyl sulfate (SDS)-polyacrylamide gel
electrophoresis is conducted to separate proteins by size.
b) The proteins migrate into the gel, and the distance they
move is inversely proportional to their size.
c)
The gel is blotted in a manner similar to Southern
blotting so that the protein bands are transferred to a
membrane.
d) The membrane is soaked in monoclonal antibodies that
are detected with a labeled secondary antibody that binds to
the primary monoclonal antibody.
e) The membrane is washed, and the places where proteins
have bound with antibody are visible and show up as bands
on the membrane.
B. Fluorescent Antibody Technique
1.
2.
3.
4.
Also called immunofluorescence microscopy, detects antigens in cells or tissues
that are bound to a microscope slide.
Uses a fluorescent tag that is bound to an antibody that is detected with a
fluorescent microscope.
The most common tag is fluorescein isothiocyanate (FITC).
Two major methods (Figure 4.27):
a) Direct assay—fluorescent antibodies are attached directly to the cell
surface. This way examines tissues for infection.
b) Indirect assay—unlabeled antibodies are first applied, followed by a
secondary fluorescent antibody specific to the unlabeled antibody. Can
detect whether antibodies are produced in response to an infection.
C.
Enzyme-Linked Immunosorbent Assay (Figure 4.28)
1.
2.
3.
Detects specific proteins, usually antibodies, in serum, and is extremely specific.
The label for the antibody is an enzyme that can catalyze a chemical reaction.
The steps of an ELISA are:
a) Bind the antigen to a plastic microplate.
b) Wash the wells of the microplate and add serum sample, so
antibodies can react to the antigen if they are made.
c)
Wash wells and add a secondary antibody specific for the antibody in
the serum to the plate. This antibody is labeled with the enzyme.
d) Wash the wells and treat the plate with the enzyme’s substrate.
e) A color change is a positive result, which can be quantified based on
the intensity of color developed.