Download The Immune System

BY: Edelia Vazquez,
Karina Delacruz,
Marisol Lopez,
and Rudy Garcia
Ms. Guillory’s Anatomy and Phy. H class.
p. 2
Your immune system protects
you from many infections.
When a foreign organism enters
your body, your immune system
recognizes the invading organism,
and destroys it in order to protect
you.
 Most people's immune system

protects them from the flu.


Defense against infectious organisms and other invaders; thus the immune
response
Enables your body to know the difference between yourself and outside germs.
◦ They communicate with each other

Two important tasks are: Killing and remembering, by recognizing foreign
invaders
◦



Equipped with to recognize the invaders
The Pathogens release chemicals and proteins that our immune defense recognizes,
triggering the kill response
Communicate with signals that stimulate them to produce antibodies
Stick with invaders in order for killing cells to recognize the pathogens
Parts of
the
Immune
System

Lymphoid Organs:
◦ A fibrous connective tissue capsule separates lymphoid organs from
surrounding tissues. These Organs include the lymph nodes, the thymus, and the spleen.

Lymph Nodes:
◦
◦
◦
◦
◦

Small, oval lymphoid organs ranging in a diameter from 1 to 25 mm
Filters and purifies lymph before that fluid reaches the venous circulation
As lymph flows through a lymph node, at least 99 percent of the antigens in the lymph are removed
Fixed macrophages in the walls of the lymphatic sinuses engulf debris or pathogens in lymph as it flows past
Antigens removed in this way are then processed by the macrophages and “presented” to nearby lymphocytes.
Thymus:
◦ Lives in your chest
◦ Located between the sternum and heart
◦ Most important in New Born Babies
◦ Without it, the body would just die
◦ As to in Humans/Adults the thymus can
be removed and will be no problem
◦ Produces T-cells:
 They are used to help measure the immune system’s
health
◦ The thymus produces several hormones that
are important to the development and maintenance of
normal immunological defenses.
Parts of the Immune System
continued

The Spleen:
• The adult spleen contains the largest collection of lymphoid
tissue in the body
• In gross dissection, the spleen is deep red owing to
the blood it contains
• Functions of spleen:
•
1.) The removal of abnormal blood cells and other blood
components by phagocytosis
•
2.) the storage of iron from recycled red blood cells
•
3.) the initiation of immune responses by B-cells and
T-cells in response to antigens in circulating blood

White Blood cells
• Most important part in the immune system
• Big collection of other cells working together
to eliminate viruses and bacteria
• Types of leukocytes:
• lymphocytes, Eosinophils, basophils, monocytes,
and neutrophils

Antibodies:
o Any of numerous Y-shaped protein molecules produced
by B-cells as a primary immune defense
o each molecule and its clone having a unique boning
site that can combine with the complementary site for a foreign
antigen, as on a virus or bacterium, thereby disabling the antigen
and signaling other immune defenses.

Epidermis:
◦ The outer, nonvascular, nonsensitive layer of the skin, covering the true skin or corium
◦ Skin provides protection from foreign invaders
 Apart from physical barrier there are specialized cells of the immune system throughout the
layers of skin
 Some of these cells detect invasion by foreign proteins such as bacteria or viruses and other cells
have the function of destroying and removing such material

Mechanical removal
◦
is the process of physically flushing microbes from the body. Methods include:
 a. mucus and cilia
 Mucus traps microorganisms and prevents them from reaching and colonizing the mucosal epithelium.
Mucus also contains lysozyme to degrade bacterial peptidoglycan, an antibody called secretory Ig, that
prevents microbes from attaching to mucosal cells and traps them in the mucus, lactoferrin to bind iron and
keep it from being used by microbes, and lactoperoxidase to generate toxic superoxide radicals that kill
microbes. Cilia on the surface of the epithelial cells propels mucus and trapped microbes upwards towards the
throat where it is swallowed and the microbes are killed in the stomach. This is sometimes called the tracheal
toilet.
 b. the cough and sneeze reflex
 Coughing and sneezing removes mucus and trapped microbes.
 c. vomiting and diarrhea
 These processes remove pathogens and toxins in the gastrointestinal tract.
 d. the physical flushing action of body fluids
 Fluids such as urine, tears, saliva, perspiration, and blood from injured blood vessels also flush microbes
from the body.

The human body has multiple defense mechanisms, but these can be sorted into two
general categories:
◦ 1.) Nonspecific defenses do not distinguish one type of threat from another.
Their response is the same, regardless of the type of invading agent. These defenses, which
are present at birth, include physical barriers, phagocytic cells, immunological
surveillance, interferon's, complement, inflammation, and fever. They provide a
defensive capability known as nonspecific resistance.
◦
2.) Specific Defenses protect against particular threats. For example, a specific defense
may protect against infection by one type of bacterium but ignore other bacteria and
viruses. Many specific defenses develop after birth as a result of accidental or
deliberate exposure to environmental hazards. Specific defenses depend on the
activities of lymphocytes. The body’s specific defenses produce a state of protection
known as immunity, or specific resistance.
There are 7 nonspecific defenses:
1.
2.
3.
4.
5.
6.
7.
Physical barriers keep hazardous organisms and
materials outside the body. For example, a mosquito
that lands on your head may be unable to reach the
surface of the scalp if you have a full head of hair.
Phagocytes are cells that engulf pathogens and cell
debris. Examples of phagocytes are the macrophages
of peripheral tissues and microphages of blood.
Immunological surveillance is the destruction of
abnormal cells by NK cells in Peripheral tissues.
Interferon's are chemical messengers that coordinate
the defenses against viral infection.
Complement is a system of circulating proteins that
assist antibodies in the destruction of pathogens.
The inflammatory response is a local response to
injury or infection that is directed at the tissue level.
Inflammation tends to restrict the spread of an
injury as well as combat an infection.
Fever is an elevation of the body temperature that
accelerates tissue metabolism and defenses.

1.
2.

Specific resistance, or immunity, is provided by the coordinated activities of
T cells and B cells, which respond to the presence of specific antigens. The
basic functional relationship can be summarized as follows:
T cells are responsible for cell-mediated immunity (or cellular immunity),
our defense against abnormal cells and pathogens inside cells.
B cells provide antibody – mediated immunity (or humoral immunity), our
defense against antigens and pathogens in body fluids.
Both mechanisms are important, because they come into play under different
circumstances. Activated T cells do not respond to antigenic materials in
solution, and the antibodies produced by activated B cells cannot cross cell
membranes. Moreover, helper T cells play a crucial role in antibody-mediated
immunity by stimulating the activity of B cells.
Immunity is either innate or acquired.

Innate Immunity
Innate Immunity is genetically determined; it is present at birth and has no relationship to previous
exposure to the antigen involved. For example , people do not get the same diseases goldfish do. Innate
Immunity breaks down only in the case of AIDS or other conditions that depress all aspects of specific
resistance.

Acquired Immunity
Acquired Immunity is not present at birth; you acquire immunity to a specific antigen only once you
have been exposed to that antigen. Acquired Immunity can be active or passive. Active Immunity
appears after exposure to an antigen, as a consequence of the immune response. The Immune system is
capable of defending against a large number of antigens. The appropriate defenses are mobilized only
after you encounter a particular antigen. Active acquired immunity can develop as a result of (1)
natural exposure to an antigen in the environment (naturally acquired immunity) or (2) from
deliberate exposure to an antigen (induced active immunity). Naturally acquired immunity normally
begins to develop after birth, and it is continually enhanced as you encounter “new” pathogens or other
antigens. The purpose of induced active immunity is to stimulate antibody production under
controlled conditions so that you will be able to overcome natural exposure to the pathogen some time in
the future. This is the basic principle behind immunization, or vaccination, to prevent disease. A
vaccine is a preparation that contains either a dead or an inactive pathogen or antigens derived from
that pathogen. Vaccines are designed to induce an immune response.

Passive Immunity
Naturally passive immunity are antibodies acquired from the mother. Induced passive immunity works
by an injection of antibodies. For example, antibodies that attack the rabies virus are injected into a
person bitten by a rabid animal.

Immunity exhibits four general properties: (1) specificity, (2) versatility, (3) memory, and (4)
tolerance.
Specificity
A specific defense is activated by a specific antigen, and the immune response targets that particular
antigen and no others. Specificity results from the activation of appropriate lymphocytes and the
production of antibodies with targeted effects.

Versatility
Millions of antigens in the environment can pose a threat to health. Over a normal lifetime, an individual
encounters only a fraction of that number, perhaps tens of thousands of antigens. The Immune
system has no way of anticipating which antigens it will encounter. It must be ready to confront any
antigen at any time. Versatility results in part from the large diversity of lymphocytes present in the
body and in part from variability in the structure of synthesized antibodies.

Memory
The Immune System “remembers” antigens that it encounters. As a result of this memory, the Immune
Response that occurs after a second exposure to an antigen is stronger and lasts longer than the
response to the first exposure.

Tolerance
The Immune system does not respond to all antigens. For example, all cells and tissues in the body
contain some antigens that normally fail to stimulate an immune response. The Immune System is
said to exhibit tolerance toward such antigen.


When an antigen triggers an immune response, it usually activates both T cells and B cells. The
activation of T cells, which usually occurs first, involves active phagocytes exposed to the antigen. Once
activated, T cells attack the antigen and stimulate the activation of B cells. Activated B cells mature
into cells that produce antibodies; antibodies distributed in the bloodstream bind to and attack the
antigen.

T cells and cell – mediated Immunity
T cells play a key role in the initiation, maintenance, and control of the immune response.
Three major types of T cells include:
1. Cytotoxic T cells (TC), which are responsible for cell mediated immunity. They enter
peripheral tissues and directly attack antigens physically and chemically.
2. Helper T Cells (TH), Which stimulate the responses of both T cells and B cells. They are
absolutely vital to the immune response, because B cells must be activated by the helper
T cells before B cells can produce antibodies.
3. Suppressor T cells (TS), which inhibit T cell and B cell activities and moderate the
immune response.
 T cell Activation
Before an immune response can begin, T cells must be activated by exposure to an antigen.
This activation seldom happens by direct lymphocyte-antigen interaction, and foreign
compounds or pathogens entering a tissue commonly fail to stimulate an immediate
immune response.

T cells only recognize antigens that are bound to glycoprotein's in cell membranes
Antigen Presentation:


Also called cluster of differentiation
markers:
◦ in T cell membranes
◦ molecular mechanism of antigen
recognition
◦ more than 70 types:
 designated by an identifying
number
CD3 Receptor Complex
Found in all T cells
CD8 Markers


Found on cytotoxic T cells and
suppressor T cells
Respond to antigens on Class I
MHC proteins
◦ CD4 Markers




Found on helper T cells
Respond to antigens on Class II MHC
proteins
CD8 or CD4 Markers - Bind to CD3
receptor complex
Prepare cell for activation
Costimulation


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For T cell to be activated, it must be
costimulated:
◦ by binding to stimulating cell at second
site
◦ which confirms the first signal
2 Classes of CD8 T Cells
Activated by exposure to antigens on MHC
proteins:
◦ one responds quickly:
 producing cytotoxic T cells and memory
T cells
◦ the other responds slowly:
 producing suppressor T cells
Also called killer T cells
Seek out and
immediately destroy
target cells
Figure 22–17 (Navigator)
Release perforin:
◦
to destroy antigenic cell membrane
Secrete poisonous lymphotoxin:
◦
to destroy target cell
Activate genes in target cell:
◦
that cause cell to die
1.
2.
3.
Slow Response
Can take up to 2 days from time of first exposure
to an
antigen, for cytotoxic T cells to reach effective
levels
Memory Tc Cells



Produced with cytotoxic T cells
Stay in circulation
Immediately form cytotoxic T cells:
◦ if same antigen appears again

Suppressor T Cells

Secrete suppression factors
Inhibit responses of T and B cells
After initial immune response
Limit immune reaction to single
stimulus



Helper T Cells - Activated CD4 T cells
divide into:
active helper T cells:
secrete cytokines
memory T cells:
remain in reserve →↓
←←←←←←←←
4 functions of Cytokines
1.
2.
3.
4.
Stimulate T cell divisions:
produce memory T cells
accelerate cytotoxic T cell
maturation
Attract and stimulate
macrophages
Attract and stimulate NK cells
Promote activation of B cells
Figure 22–18
Figure 22–19



Cell-mediated immunity involves close physical
contact between activated Tc cells and foreign,
abnormal or infected cells
T cell activation usually involves:
◦ antigen presentation by phagocytic cell
◦ costimulation by cytokines from active phagocytes
Tc cells may destroy target cells through local release of
cytokines, lymphotoxins, or perforin



Responsible for antibody-mediated immunity
Attack antigens by producing specific antibodies
Millions of populations, each with different antibody
molecules
B Cell Sensitization



Corresponding antigens in interstitial fluids bind to B cell
receptors
B cell prepares for activation
Preparation process is sensitization
During sensitization,
antigens are:
taken into the B
cell, processed,
reappear on surface,
bound to Class II
MHC protein
Figure 22–20 (Navigator)


Sensitized B cell is prepared for activation, but needs helper T cell
activated by same antigen
B Cell Activation
Helper T cell binds to MHC complex:
◦ secretes cytokines that promote B cell activation and division
B Cell Division

Activated B cell divides into:
◦ plasma cells -Synthesize and secrete antibodies into interstitial fluid
Memory B cells- Like memory T cells remain in reserve to respond to
next infection
What is the
structure of
an antibody, and
what types
of antibodies are
found in body
fluids and
secretions
Figure 22–21a, b


2 parallel pairs of polypeptide chains:
◦ 1 pair of heavy chains
◦ 1 pair of light chains
Each chain contains:
◦ constant segments
◦ variable segments-Determine
specificity of antibody molecule
•Antigen–Antibody
Complex = An antibody
bound to an antigen


2 parallel pairs of polypeptide chains:
◦ 1 pair of heavy chains
◦ 1 pair of light chains
Each chain contains:
◦ constant segments
◦ variable segments-Determine specificity of antibody molecule
5 Heavy-Chain

Constant Segments
Determine 5 types of antibodies:
◦ IgG
◦ IgE
◦ IgD
◦ IgM
◦ IgA


Free tips of 2 variable segments:
◦ form antigen binding sites of antibody molecule
◦ which bind to antigenic determinant sites of antigen molecule
Antibody Function
A Complete Antigen



Has 2 antigenic determinant sites
Binds to both of antigen binding sites of variable segments of antibody
Exposure to a complete antigen leads to:
◦ B cell sensitization
◦ immune response
A Hapten




Also called partial antigen
Must attach to a carrier molecule to act as a complete antigen
Dangers of Haptens
Antibodies produced attack both hapten and carrier molecule
If carrier is “normal”:
◦ antibody attacks normal cells
◦ e.g., penicillin allergy




Also called immunoglobins (Igs)
Are found in body fluids
Are determined by constant segments
Have no effect on antibody specificity
7 Functions of
Antigen–Antibody Complexes
1.
2.
3.
4.
5.
6.
7.
Neutralization of antigen binding sites
Precipitation and agglutination:
◦
formation of immune complex
Activation of complement
Attraction of phagocytes
Opsonization:
◦
increasing phagocyte efficiency
Stimulation of inflammation
Prevention of bacterial and viral adhesion



Antibody-mediated immunity involves the production of
specific antibodies by plasma cells derived from activated B
cells
B cell activation usually involves:
◦ antigen recognition, through binding to surface antibodies,
costimulation by a Th cell
Antibodies produced by active plasma cells bind to target
antigen and:
◦ inhibit its activity or destroy it
◦ remove it from solution
◦ promote its phagocytosis by other defense cells

Occur in both cell-mediated and antibody-mediated
immunity
Figure 22–22



First exposure:
◦ produces initial response
(Primary)
Next exposure:
◦ triggers secondary response
◦ more extensive and
prolonged
◦ memory cells already
primed





Takes time to develop
Antigens activate B cells
Plasma cells differentiate
Antibody titer slowly rises
Peak response:
◦ can take 2 weeks to develop
◦ declines rapidly
IgM:
◦ is produced faster than IgG
◦ is less effective
The Secondary Response



Activates memory B cells:
◦ at lower antigen concentrations than
original B cells
◦ secrete antibodies in massive qualities
Effects of Memory B Cell Activation
IgG:
◦ rises very high and very quickly
◦ can remain elevated for extended time
IgM:
◦ production is also quicker
◦ slightly extended


Immunization produces a primary response to a
specific antigen under controlled conditions
If the same antigen appears at a later date, it triggers
a powerful secondary response that is usually
sufficient to prevent infection and disease

Specific and nonspecific defenses
Figure 22–23
Figure 22–24
Figure 22–25





Neutrophils and NK cells begin killing bacteria
Cytokines draw phagocytes to area
Antigen presentation activates:
◦ helper T cells
◦ cytotoxic T cells
B cells activate and differentiate
Plasma cells increase antibody levels
Combined Responses
to Viral Infection


Similar to bacterial infection
But cytotoxic T cells and NK cells are activated by contact with virus-infected
cells
Table 22–2

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

Viruses replicate inside cells, whereas bacteria may live independently
Antibodies (and administered antibiotics) work outside cells, so are primarily effective against bacteria
rather than viruses
Antibiotics cannot fight the common cold or flu
T cells, NK cells, and interferons are the primary defense against viral infection
Immune System development

Fetus can produce immune response or immunological competence:
◦ after exposure to antigen
◦ at about 3–4 months
Development of
Immunological Competence



Fetal thymus cells migrate to tissues that form T cells
Liver and bone marrow produce B cells
4-month fetus produces IgM antibodies


Maternal IgG antibodies:
◦ pass through placenta
◦ provide passive immunity to fetus
After Birth
Mother’s milk provides IgA antibodies:
◦ while passive immunity is lost
Normal Resistence:


Infant produces IgG antibodies through exposure to antigens
Antibody, B-cell, and T-cell levels slowly rise to adult levels:
◦ about age 12
1.
2.
3.
4.
5.
6.
Interleukins
Interferons
Tumor necrosis factors
Chemicals that regulate phagocytic activities
Colony stimulating factors
Miscellaneous cytokines
Autoimmune disorders- A malfunction of system that recognizes and ignores “normal” antigens
Activated B cells make autoantibodies against body cells

Immunodeficiency diseaseThyroiditis
Rheumatoid arthritis
Insulin-dependent diabetes mellitus

Allergies –

Immunodeficiency Diseases
1.
2.
3.
Problems with embryological development of lymphoid tissues:
◦
can result in severe combined immunodeficiency disease (SCID)
Viral infections such as HIV:
◦
can result in AIDS
Immunosuppressive drugs or radiation treatments:
◦
can lead to complete immunological failure


Inappropriate or excessive immune responses to antigens
Allergens:
◦ antigens that trigger allergic reactions
4 Categories of Allergic Reactions




Type I:
◦ immediate hypersensitivity
Type II:
◦ cytotoxic reactions
Type III:
◦ immune complex disorders
Type IV:
◦ delayed hypersensitivity






Also called immediate hypersensitivity
A rapid and severe response to the presence of an antigen
Most commonly recognized type of allergy
Includes allergic rhinitis (environmental allergies)
Sensitization leads to:
◦ production of large quantities of IgE antibodies
◦ distributed throughout the body
Second exposure leads to:
◦ massive inflammation of affected tissues
Type I Allergy (2)


Severity of reaction depends on:
◦ individual sensitivity
◦ locations involved
Allergens in blood stream may cause anaphylaxis





Can be fatal
Affects cells throughout body
Changes capillary permeability:
◦ produce swelling (hives) on skin
Smooth muscles of respiratory system contract:
◦ make breathing difficult
Peripheral vasodilatation:
◦ can cause circulatory collapse (anaphylactic shock)
Antihistamine Drugs


Block histamine released by MAST cells
Can relive mild symptoms of immediate hypersensitivity
Stress and the Immune Response

Glucocorticoids:
◦ secreted to limit immune response
◦ long-term secretion (chronic stress):
 inhibits immune response
 lowers resistance to disease



Depression of the inflammatory response
Reduction in abundance and activity of phagocytes
Inhibition of interleukin secretion
Aging and the Immune Response
Immune system deteriorates with age, increasing vulnerability to infections and cancer
4 Effects of Aging on Immune Response
1.
2.
3.
4.
Thymic hormone production:
◦
greatly reduced
T cells:
◦
become less responsive to antigens
Fewer T cells reduce responsiveness of B cells
Immune surveillance against tumor cells declines
Nervous and
Endocrine Systems
Interact with thymic
hormones
Adjust sensitivity of
immune
Figure 22–27


The relationship among the cells of the Immune response and the nervous and
endocrine systems are now the focus of intense research.
For examples, the cells of the immune system can influence central nervous
system (CNS) and endocrine activity.

3 categories affect immune response:
◦ disorders resulting from:
 an insufficient immune response
 an inappropriate immune response
 an excessive immune response

Before vaccines were invented the only way to create immunity in the body was to suffer
through a bout of the disease in question. Once endured, providing you survived, your immune
system could fight off any future infections before they took hold. B-cells in the bloodstream,
responsible for fighting off the disease, retain memory of the disease. If the disease returned,
the immune system launched a quick attack before the disease could take hold.
 When people get vaccinated:
 Vaccination is inserted into body, it is “basically” the disease or “sickness” in a more weakened form.
 Once inserted, the body examines the new substance that is found in the body and therefore protects immunity.
 In the future, in case you get sick, the body and the immune system are prepared to fight it off and prevent you
from getting sick.

All vaccinations work by presenting a foreign antigen to the immune system in
order to evoke an immune response, there are several ways to do so. The four
main types that are currently in clinical use are as follows:
 An inactivated vaccine consists of virus particles which grown in culture and then killed using a method such
as heat or formaldehyde
 In an attenuated vaccine, live virus particles with very low virulence are
Administered. They will produce, but very slowly.
 Virus-like particle vaccines consists of viral protein(s) derived from the structural
Proteins of a virus.
 A subunit vaccine presents an antigen to the immune system without introducing
Viral particles, whole or otherwise.
 Measles

can be prevented by vaccinations. All children should be vaccinated to protect themselves. Given to children beginning with 12 months.
 Polio
 Is caused by a virus that lives in the intestinal tract and sometimes in the throat
 Was eliminated from the U.S in 1979.
 Still exists in some developing countries.
 Symptoms of Polio:
 Include:

Fever

Fatigue

Headache

Vomiting

Stiffness in the neck

pain in the limbs
Up to 95% of all persons infected with polio will have no symptoms
The best way to prevent polio is for all children to be fully vaccinated on time.
The inactivated polio vaccine (IPV) protects against polio.

H1N1 Vaccine:
◦ Vaccines to protect against the 2009 H1N1 virus (also called the “swine flu”) have been
produced. Like seasonal flu vaccines, there are two kinds of 2009 H1N1 vaccines: a "flu
shot "; that is given with a needle, usually in the arm; and a nasal spray flu vaccine .
The same manufacturers that produce seasonal flu vaccines also produced the vaccines
against the pandemic 2009 H1N1 virus in the same way that the seasonal vaccines are
made. Vaccines to protect against 2009 H1N1 are widely available. CDC is now
encouraging everyone to get vaccinated against 2009 H1N1, including people 65 years
and older.

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Did you know?
◦ Getting under 5 hours of sleep a night has been shown to significantly
depress the Immune Response.
A germ can be considered a virus, bacteria, fungi, protozoan, and etc.
Once a germ invades the body it quickly multiplies, how can you get rid of
them now!
We should have a Healthy Immune System, and it fights back by sending
white blood cells to destroy the invaders.
While the T-cells surround the invaders, they “eat” them
Then, chemically notify the B-cells which produce antibodies that destroy the
germs
There are some germs that survive the attack, which can cause illness.
Antibiotics help to finally destroy all the germs and NORMAL health is
restored.