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Chapter 22:
Lymphatic System
and Immunity
BIOL 2402
Introduction
• The ability of the body to protect itself
from damage or disease is called
resistance. Two main types of resistance
are:
– Nonspecific resistance (innate defenses):
provide defense mechanism against a range of
pathogens in a general way.
– Specific resistance (immunity): provides
defense mechanism against a specific
pathogen by specialized lymphocytes.
• The system of the body responsible for specific
resistance is the lymphatic system.
Functions of the
Lymphatic System
• Fluid balance
– Excess interstitial fluid enters lymphatic
capillaries and becomes lymph. Finally drained
into the circulatory system.
• Fat Absorption
– Lymphatic system helps to absorb fat and other
substances from the digestive system with the
help of specialized vessels called lacteals.
• Defense
– Lymphocytes residing in the lymphatic tissues of
the body, protect the body against
microorganisms and foreign substances.
Lymphatic Structures
Lymphatic System
consists of:
• Lymph: A fluid similar
to plasma but does
not have plasma
proteins.
• Lymphatic vessels
(lymphatics): Carry
lymph from peripheral
tissues to the venous
system
• Lymphoid tissues and
lymphoid organs.
• Lymphocytes,
phagocytes, and other
immune system cells.
Components of the Lymphatic System
Lymph: fluid drained from interstitial spaces in all
tissues of the body. Composition equivalent to
the interstitial fluid.
• Returns to circulatory system via Lymphatic
vessels; essential for fluid balance.
• Lymph  Lymphatic Capillaries  Lymphatic
vessels  Lymph nodes  lymphatic trunk 
Lymphatic duct  Drain into large veins of the
body.
Lymphatic Capillaries
• Lymph capillaries: Very
similar to blood capillaries
in structure with 2
modifications.
– First Lymphatic
capillaries have
endothelial cells which
are loosely attached
and are therefore more
permeable.
– Secondly the lymphatic
capillaries have one
way valves to prevent
back flow of lymph into
interstitial space.
Lymphatic Vessels
• Lymph capillaries merge to form lymphatic vessels which have
valves and are similar in structure to veins.
– They have all three layers and one way valves.
– Lymph moves through the vessels with the help of milking action
carried out by the skeletal muscles and pressure changes created by
the respiration.
• Lymph nodes: bean-shaped clusters of B and T cells found at
intervals along the length of the vessels; lymph flows through the
nodes.
– Function to filter lymph.
Lymph Lymphatic vessels/ Trunks
• As lymphatic vessels exit from lymph nodes, they
merge and form lymph trunks
• Each lymphatic trunk drains fluid from a certain
area of the body.
• e.g. jugular trunks drain from the head and neck,
subclavian trunks drain from the upper arms and
superficial thoracic wall.
Lymph Ducts
• Lymphatic trunks drain into two lymphatic ducts
– Thoracic duct: Main collecting duct of the lymphatic system.
• Receives lymph from the left side of the head, neck, and chest, the left
upper extremity, and the entire body below the ribs.
• Drains lymph into venous blood at junction of the left subclavian vein
and internal jugular vein.
– Right lymphatic duct: drains right side head, arm and chest. Empties into
venous system at junction of right subclavian vein and right jugular vein.
Lymphocytes
• Make up 20–30% of circulating leukocytes
Most are stored, not circulating
Types of Lymphocytes
T cells: Thymus-dependent
B cells: Bone marrow–derived
NK cells: Natural killer cells
Lymphocytes (contd) – T cells
• T Cells : Make up 80% of circulating lymphocytes.
Formation: Stem cells in the red bone marrow --->
divide and differentiate into blood cells->lymphocyte stem cells exit bone marrow -->
migrate to thymus gland --> mature and
differentiate in thymus --> form T-cells.
Main Types of T Cells
– Cytotoxic T (TC) cells: Attack cells infected by viruses.
Produce cell-mediated immunity
– Memory T cells TM: Formed in response to foreign
substance. Remain in body to give “immunity”
– Helper T (TH) cells: Stimulate function of T cells and B
cells
– Suppressor T (TS) cells: Inhibit function of T cells and B
cells
Lymphocytes (contd) – B cells
• - Make up 10–15% of circulating lymphocytes
• - Differentiate (change) into plasma cells which
produce and secrete antibodies (immunoglobulin
proteins).
• - Formation: Stem cells in the red bone marrow --> divide and differentiate into blood cells --> some
lymphocyte cells remain in bone marrow -->
mature and differentiate in bone marrow --> form
B-cells.
Lymphocytes (contd) – Natural Killer (NK)
cells
•
•
•
•
- Also called large granular lymphocytes
- Make up 5–10% of circulating lymphocytes
- Responsible for immunological surveillance
- Attack foreign cells, virus-infected cells, and
cancer cells
Types of Lymphocytes
Lymphatic tissues and Organs
• Classified into two groups
– Primary Lymphatic organs:
• where the lymphocytes originate and mature to become
immunocompetent.
• e.g. red bone marrow and thymus gland.
– Secondary Lymphatic organs:
• are the sites where the mature lymphocytes reside and
carry out immune response.
• e.g. spleen, lymph nodes and nodules
Lymphatic Nodules
are aggregates of lymphatic tissue not surrounded by a
capsule. Examples include
• Mucosa associated lymphatic tissue (MALT): scattered
throughout the lamina propria of mucous membranes
lining the GI tract, respiratory airways, urinary tract, and
reproductive tract.
• Peyers patches: aggregates of lymphatic tissue in
appendix and small intestines for protection
• Tonsils: large groups of nodules in the mucosa of the
pharynx. Provide protection against bacteria entering the
body through the mouth or nasal cavities.
– Pharyngeal tonsil (adenoids)
– Palatine tonsils on each side wall
– Lingual tonsil in the back of the tongue
Lymphatic nodules (tonsils)
Lymph Nodes
• Bean-shaped or oval structures located along lymphatic
vessels.
• Superficial (near skin) and deep. Concentrated near
mammary glands, axilla, groin
• Function to filter lymph
• A dense connective tissue capsule surround each lymph
node. Capsule extends in the lymph node as trabeculae.
• Outer part of the node is called cortex which is made up
of lymphatic nodules containing lymphocytes and
macrophages.
• Inner medulla is made up of irregular strands of
lymphatic tissue called medullary cords.
• Lymph enters the nodes via the afferent lymphatic vessel
and leaves via the efferent lymphatic vessel.
Lymph node structure
Metastasis Through
Lymphatic System
• Characteristic of malignant tumors
• Spread of disease from one organ to another
– cancer cells travel via blood or lymphatic
system
– cells establish new tumors where lodge
• Secondary tumor sites can be predicted by
direction of lymphatic flow from primary site
Relationship of Circulatory and
Lymphatic Systems
Thymus Gland
• Large organ in infants but atrophied as adult.
• 2 lobed organ located in mediastinum
Thymus Gland (contd)
• Surrounded by a connective tissue capsule
• Trabeculae extend from capsule and divide it into lobules
• Each lobule has cortex and
medulla
• Cortex (numerous lymphocytes) and medulla (fewer
lymphocytes)
• Site of maturation of T cells: many T cells produced here.
Spleen
• Left superior side of abdomen; can be ruptured in traumatic
abdominal injuries resulting in bleeding, shock, death
• Functions
• Destroys defective RBCs
• Detects and responds to foreign substances
• Limited reservoir for blood
• The spleen is often damaged in abdominal trauma. A
splenectomy may be required to prevent excessive bleeding.
Spleen (structure)
• Outer Layer of connective tissue called Capsule.
Extensions of the capsule called trabeculae divide the
spleen into smaller compartments.
• Each compartment is filled with white and red pulp.
White pulp is lymphatic tissue around arteries in the
spleen. Red pulp is Lymphatic tissue associated with
the veins.
• The depression on the Spleen where the splenic blood
vessels enter and leave is called hilum.
REVIEW!!!!
Now that we have completed the study of the
organization of the lymphatic system, attempt the
following questions:
• What is the function of the lymphatic vessels?
• What structure prevents the backflow of lymph in
the lymphatic vessels?
• Name the two large lymphatic ducts and the parts
of the body they drain lymph from?
• Explain lymphedema?
• Identify the three main classes of lymphocytes?
REVIEW !! (contd)
• Which cells are responsible for antibody mediated
immunity?
• Define tonsils, and name the three main ones?
• Where is the thymus gland located?
• What is the function of spleen?
• Describe red pulp and white pulp found in the
spleen?
If you are comfortable with this material move on to
the second part of the lecture outline.
Resistance
• Is defined as the ability to resist damage from
foreign substances such as microorganisms and
harmful chemicals.
• Susceptibility: lack of resistance.
• Categories
– Innate or nonspecific resistance
– Adaptive or specific immunity.
Innate (nonspecific) defense mechanisms
• Prevent entry, limit the spread of microorganisms
or other environmental hazards. There are seven
major categories of innate defenses.
1. Physical barriers
2. Phagocytes
3. Immunological surveillance
4. Interferons
5. Complement
6. Inflammatory response
7. Fever
1. Physical barrier
Prevent entry of microbes in the body. Provided by
the skin and mucous membrane.
• Intact skin is a physical barrier to entrance of
microbes.
• Mucous membrane that lines the digestive
respiratory and urogenital tract secrete a viscous
mucus that prevents entry of potentially harmful
microbes.
• In addition many of the secretions like saliva, tears
etc. also contain proteins like lysozyme which
digest cell wall of microbes and destroy it.
1. Physical barrier (contd)
2. Phagocytes
Phagocytes are specialized cells that perform
phagocytosis. Phagocytosis takes place in 5 steps
chemotaxis, adherence, ingestion, digestion, and
killing. Cells involved in this process include:
• Neutrophils:- 60-70% of all WBCs. They leave
blood and migrate to the infected area, attracted
to the chemicals released by the damaged cells.
They self destruct on destroying foreign invaders.
• Monocytes:- 5% of WBC. They leave the blood,
migrate into tissues and develop into
macrophages. Some macrophages are wandering
(moving around the body) and others are fixed
(stationary). They extend pseudopodia and pull
the microbes in.
3. Immunological surveillance
Is carried out by natural killer (NK) cells. They attack
cancer cells and body cells infected with viruses.
Their mechanism of action is outlined below:
• Activated NK Cells identify and attach to abnormal
cell (nonselective)
• Golgi apparatus in NK cell forms perforin vesicles
• Vesicles release proteins called perforins
(exocytosis)
• Perforins lyse abnormal plasma membrane
3. Immunological surveillance (contd)
4. Interferons
Inteferons:- are chemicals released by virus
infected cells.
• They cannot save the infected cell, but they
diffuse to neighboring healthy cells, where they
stimulate the production of antiviral proteins
that inhibit viral replication in these cells. Thus
an infected cell helps to protect uninfected cells.
• There are three known types of interferons,
alpha, beta, gamma. - are most effective in
controlling short term infections, such as cold
and influenza.
5. Complement System
Plasma contains 11 special complement (C)
proteins. These proteins form complement
system and complement antibody action.
Complement proteins work together in
cascades.
Two pathways activate the complement system: Classical
pathway and Alternative pathway
Effects of Complement Activation
Pore formation: Destruction of target plasma
membranes. Five complement proteins join to form
membrane attack complex (MAC)
• Enhancement of phagocytosis by opsonization.
Complements working with antibodies (opsonins)
• Histamine release: Increases the degree of local
inflammation and blood flow
6. Inflammation
• is triggered by a physical injury, such as a cut, or by
entry of microorganisms.
• Symptoms include redness, pain, heat and swelling.
• An injury to white blood cells called, basophils &
mast cells causes release of histamine which
triggers vasodilations.
• Small blood vessels near the injury dilate, increasing
the blood supply (causing redness & heat). Fluids
from the dilated vessels also move into neighboring
tissues, causing swelling.
• Inflammatory response also involves the migration of
phagocyte from the blood into the infected tissues,
which eliminate the pathogens by phagocytosis.
Inflammation
Products of
Inflammation:
Necrosis: Local tissue
destruction in area of
injury
Pus: Mixture of debris
and necrotic tissue
Abscess: Pus
accumulated in an
enclosed space
7. Fever
Fever : is defined as a maintained body temperature
above 37 0C (99 0F)
Pyrogens: Any material that causes the
hypothalamus to raise body temperature.
• A variety of stimuli either act as pyrogens
themselves or stimulate macrophages to release
pyrogens, e.g. Circulating pathogens, toxins, or
antibody complexes.
• Active macrophages release cytokine called
endogenous pyrogens or interleukin-1 (IL-1).
Specific (adaptive) defense mechanisms
• Responds to specific antigens
• With coordinated action of T cells and B cells
• Specific Defenses
– T Cells: Provide cell-mediated immunity
Defend against abnormal cells and pathogens inside
cells
– B Cells: Provide antibody-mediated immunity
Defend against antigens and pathogens in body fluids
Specific Resistance: Immunity
• Operates after the microbe has crossed the nonspecific line
of defense
• 4 characteristic features of the immune system are:– Specificity:- recognition of a specific pathogen or toxin
and then destroying it. Each lymphocyte is highly
specific in responding to a particular pathogen or toxin.
– Diversity:- Immune system on the whole has the ability
to respond to millions of different kind of invaders.
– Memory:- Immune system has the ability to ‘remember’
pathogens or toxins it encounters. This property is
carried out by specialized cells termed the memory cells.
– Self/nonself recognition:- Immune system distinguishes
the body's own molecules from foreign molecules.
Specific Resistance: Immunity (contd)
• Types of Immune Responses:
•
•
– Cell mediated immunity: works best against intracellular
antigens which invade and are present in an infected cell.
e.g. viruses, parasites, fungi and cancer cells and tissue
transplants. Antigens bind to a specific T-cell receptor --> Tcell becomes activated and differentiates into Killer cell and
directly attacks the infected cell causing its lysis.
– Humoral or antibody mediated response: In this response
antigens trigger and activate a specific B-cell --> which
differentiates into plasma cells & reacts by producing
antibodies --> which are released in the blood and
lymph. These antibodies then inactivate the foreign antigen
by a number of possible mechanisms. This type of immune
response works against extracellular antigens circulating in
body's fluid.
Often a pathogen provokes both types of immune response
Some T cells act as intermediaries between antibody-mediated
and cell-mediated immunity.
Key Terminologies used in Immunity
• Antigen: A foreign molecule capable of triggering a response
form the adaptive Immunity.
– e.g. of antigens - bacteria, viruses, fungi, protozoa, pollens, &
transplanted tissue.
• Required characteristics to be considered an antigen
– immunogenicity = ability to provoke immune response
– reactivity = ability to react to cells or
antibodies it caused to be formed
• Epitope:- localized region on the surface of an
antigen capable of initiating immune response,
is called epitope. A single antigen can have
several effective epitopes.
• Hapten: are small molecules that bind to larger
molecules within the body and then stimulate
an adaptive Immunity response. E.g. penicillin
• Foreign antigens: not produced in the body.
• Allergens: cause an overreaction of the Immune system.
• Self antigens: molecules within the body triggering immune
system. Can prove to be dangerous – autoimmune diseases.
Diversity of Antigen Receptors
• Immune system can recognize and respond to a
billion different epitopes -- even artificially made
molecules. This recognition is done with the help
of specific receptors.
– Antigen receptors: site on B or T cells that can bind
epitopes.
– Each B or T cell has its own unique set of gene segments
that codes for unique antigen receptor inserted in the
cell membrane.
Major Histocompatibility Complex
• B cells and T cells must have the ability to recognize both
molecules that are antigenic (non-self) and self antigens. This
recognition is done via the MHC molecules.
• Major histocompatability complex (MHC) antigens:
glycoproteins found on the surface of cells. Unique for each
genetically different individual – serve as identity markers.
• B and T-cell receptors do not elicit any response against body's
own MHCs, but when the MHC is attached to a foreign antigen it
initiates an immune response in the body.
• Two classes of MHCs are:
– Class I (MHC-1): found on surface of all cells except RBCs.
– Class II (MHC-2): are produced and appear on the surface of
specialized cells called antigen-presenting cells (APCs).
Processing of exogenous antigens
• Exogenous antigens are the ones present outside body
cells, e.g. bacteria, parasitic orms, bacterial toxins.
• Cells that help to process and present exogenous
antigens are called the antigen-presenting cells (APCs)
which include macrophages, B cells, and dendritic cells.
• The steps in this process are:
– APCs ingest antigens by phagocytosis.
– Inside the APCs, the antigen is digested
into shorter pieces.
– APCs synthesize MHC-II molecules.
– Inside the APCs, MHC-II molecules and the
antigen pieces bind to one another.
– MHC-II-antigen complex is then inserted in the
plasma membrane of the APC. This APC then
migrates to lymphatic tissue to present the
antigen to the T cells.
– APC migrates to lymphatic tissue to find T cells
– Display of MHCII with foreign antigen is like
“Rally round the flag”, stimulates other immune
system cells to respond to the antigen.
Processing of Exogenous Antigens
Processing of endogenous antigens
• Endogenous antigens are synthesized
within the body and include viral proteins
or proteins produced by cancer cells.
• Most of the cells of the body can process
endogenous antigens
• Fragments of endogenous antigen are
associated with MHCI molecules inside the
cell.
• The antigen MHCI complex moves to the
cell’s surface. This complex signals the
lymphatic system that a cell has been
infected and needs help.
Processing of Endogenous antigens (contd)
Cell-Mediated Immunity
• Works best against intracellular antigens which invade and are
present in an infected cell. e.g. viruses, parasites, fungi and
cancer cells and tissue transplants.
• In order for T cells to defend the body they must be activated,
proliferate and differentiate into effector cells
– Antigen Recognition: Binding of the T cell receptor with
antigen on antigen presenting cell.
– Costmulation: Involves costimulation by cytokines such as
interleukin-1 and interleukin-2.
– Activation by CD4 or CD8 cells: enlargement then mitosis
of the activated T cell into many cells.These cells
differentiate into effectors: helper T cells, cytotoxic T cells,
and memory T cells
• Only a few T cells are activated but this results in thousands of
differentiated T cells.
Antigen Recognition
• T cell receptors recognize antigen fragments
associated with MHC molecules on the surface of
a body cell.
• CD Markers are cluster of proteins on T cell
membranes that play an important role in antigen
recognition.
Two important CD markers are:
– 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
Costimulation
• Proliferation of T cells requires costimulation, by
cytokines such as interleukin-1 (IL-1) and
interleukin-2 (IL-2), or by pairs of plasma
membrane molecules, one on the surface of the T
cell and a second on the surface of an APC.
Activation of CD8 cells
• Activated by exposure to antigens on MHC
protein.
• Results in the production of two types of T cells:
TC and Memory T cells
• Cytotoxic T cells Seek out and immediately destroy
target cells by using several different mechanisms.
• Memory TC Cells: Stay in circulation and
Immediately form cytotoxic T cells if same antige n
appears again.
Activation of CD4 cells
• Upon activation, undergo a series of divisions and
differentiate into:
• Active helper T cells (TH cells): Secrete cytokines
that stimulate both cell-mediated and antibodymediated immunity.
• Memory helper (TH) cells: Remain in reserve
Antibody Mediated Immunity
B Cells
• Responsible for antibody-mediated immunity
• Attack antigens by producing specific antibodies
• Millions of populations, each with different
antibody molecules
• This type of immune response works against extra
cellular antigens circulating in body's fluid.
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
B Cell Activation
• Helper T cell binds to MHC complex
• Secretes cytokines that promote B cell activation and division
B Cell Differentiation
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.
Antibodies
• Antibodies constitute a class of proteins called Immunoglobulins
(Igs ).
• Antibody can be either T- or Y-shaped.
• Four polypeptide chains: two heavy and two light. Each light is
held to a heavy by a disulfide bond.
• Each chain has two regions; a constant region (C) which is the
same within a class of antibody and a variable region (V) which
varies from one antibody to the other.
• V region from each chain has the antigen binding site to
recognize and specifically attach to a particular antigen.
Antibodies (contd)
•
Based on chemistry and structure, antibodies are grouped into five principal
classes each with specific biological roles (IgG, IgA, IgM, IgD, and IgE).
Antibody Action
Antigen–Antibody Complexes can destroy the antigen in one of
the following ways:
• Neutralization of antigen binding sites: antibodies bind to
specific sites on bacteria and viruses which prevents them
from attaching to a body cell.
• Precipitation and agglutination - antibodies link large
number of antigens togetehr, resulting in the formation of
immune complex which becomes too large and therefore
precipitates.
• Activation of complement
• Attraction of phagocytes
• Opsonization: coating of an antigen by antibodies is called
opsonization, which increases phagocyte efficiency
• Stimulation of inflammation by stimulating basophils and
mast cells.
• Prevention of bacterial and viral adhesion.
Primary and Secondary Immune Response
• Primary immune response
– First exposure to antigen
response is steady, slow
– resulting in proliferation of lymphocytes to form clones of
plasma cells and memory cells.
• Secondary immune response with second exposure to the
same antigen
– Memory cells proliferate and differentiate into plasma cells
– Faster and stronger than the primary immune response.
Types of Adaptive Immunity
• Active immunity: is when the body's immune system is
stimulated to make antibodies and other immune cells (killer
cells).
• This immunity takes time to work, it generates memory cells
which protect against future encounters with the same
antigen.
• Active immunity can be naturally acquired or artificially.
– Naturally acquired active immunity: is seen when the
individual is exposed to the antigen in a natural manner.
• Body responds to this antigen by activating B and/or
T cells, and memory cells are made.
• e.g. being exposed to chicken pox virus through a
friend.
– Artificially acquired active immunity: is when a weak or
killed antigen is injected into the individual.
• Individual responds by activating a specific B and/or T
cell, and antigen is inactivated. In this process
memory cells are also made for future encounters.
• This type of immunity forms the basis for vaccination.
Types of Adaptive Immunity (contd)
• Passive immunity: is when prepared antibodies are
received by an individual.
• This immunity provides immediate protection but lasts
for a short term, since antibodies are proteins and
undergo breakdown.
• Body's immune system is not involved in this immunity
and hence no memory cells are produced.
– Naturally acquired passive immunity: e.g. when IgG naturally
crosses the placenta to go from the mother's blood to fetus
blood or when IgA is fed to the new born through the breast
milk. These antibodies work for a short period of time.
– Artificially acquired passive immunity: is when an individual is
given shots of prepared antibodies or serum to treat or
prevent infections. Shots of gamma globulins are often given
to hospital patients and travelers for temporary protection
against hepatitis.
Types of adaptive Immunity (contd)
Immune System Disorders: AIDS
• HIV is a form of retrovirus with a protein coat wrapped by an
envelope of glycoproteins.
• Host cell for HIV are the helper T cells.
• New HIV DNA is produced in the T cell along with new protein
coats and then released.
• The T cells are ultimately destroyed.
• Progression to Acquired Immunodeficiency Syndrome (AIDS)
occurs because of reduced numbers of T cells and resulting
immunodeficiency. AIDS lowers the body’s immunity by
decreasing the number of helper T cells.
• Although HIV has been isolated from several body fluids, the
only documented transmissions are by way of blood, semen,
vaginal secretions, and breast milk from an infected nursing
mother.
• Treatment of HIV infection with reverse transcriptase inhibitors
and protease inhibitors has shown to delay the progression of
HIV infection to AIDS.
Hypersensitivity Reactions: Allergies
Inappropriate or excessive immune responses to
antigens
Allergens
• Allergens: antigens that induce an allergic
reaction in some people but are tolerated by most
people.
• Allergic (hypersensitive) people respond to
allergens.
Diseases of the Immune System:
• autoimmune diseases: Immune system
initiates immune response against body’s
own cells
– Rheumatoid arthritis leads to damage and
painful inflammation of the cartilage and
bone of joints.
– In insulin-dependent diabetes mellitus, the
insulin-producing beta cells of the pancreas
are the targets of autoimmune cell-mediated
responses.
– Multiple sclerosis (MS) is the most common
chronic neurological disease.
Age Related Changes
Immune System Diminishes with Age
Increasing vulnerability to infections and cancer
Four Effects of Aging
• Thymic hormone production is greatly reduced
• T cells become less responsive to antigens
• Fewer T cells reduces responsiveness of B cells
• Immune surveillance against tumor cells declines
REVIEW!!
• Now that you have reviewed the Specific defenses of the
human body, try to answer the following questions:
Describe antigen presentation.
• What is the major histocompatibility (MHC) complex?
• Where are the class I and Class MHC molecules found?
• Describe CD markers.
• Define the function of cytokines secreted by helper T cells in
the activation of B cells?
• Describe the structure of antibody? Which part plays an
important role in antigen recognition?
• Highlight the differences between primary and secondary
immune response.
• Define allergy and allergens.
• What is anaphylaxis?
• Define autoimmune diseases and immunodeficiency
diseases.