Biology Student’s Companion Resources SB025 1 | KMPk CHAPTER 11: IMMUNITY SUBTOPIC :11.1 IMMUNE RESPONSE LEARNING OUTCOMES: (a) Define immunity and state the types of immunity (b) Describe the general structure of antibodies and state the classes based on its structure. (c) State the roles of lymphoid organs in immunity such as: i. Thymus ii. Spleen iii. Tonsil iv. Lymph nodes v. Bone marrow (d) Explain the various types of antigen and antibody interactions: i. neutralization ii. opsonization iii. activation of complement system and pore formation. MAIN IDEAS /KEY POINT EXPLANATION NOTES a. Immunity and types of immunity Immunity: The ability to recognize and destroy foreign or dangerous macromolecules (Solomon 10 th Ed, 2015). The state of having sufficient biological defenses to avoid infection, disease or other unwanted biological invasion by foreign organism or other foreign substance Types of immunity: a) Innate immunity b) Adaptive immunity INNATE IMMUNITY (all animals) Recognition of traits shared by broad ranges of pathogens, using a small set of receptors Rapid response ADAPTIVE IMMUNITY (vertebrates only) Recognition of traits specific to particular pathogens, using a vast array of receptors Slower response Barrier defenses: Skin Mucous membranes Secretions Internal defenses: Phagocytic cells Natural killer cells Antimicrobial proteins Inflammatory response Humoral response: Antibodies defend against infection in body fluids. Cell-mediated response: Cytotoxic cells defend against infection in body cells. Pathogens (example: fungi, bacteria and viruses)
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CHAPTER 11: IMMUNITY · 2021. 1. 17. · Humoral immune response The branch of adaptive immunity that involves the activation of B cells and that leads to the production of antibodies,
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Biology Student’s Companion Resources SB025
1 | KMPk
CHAPTER 11: IMMUNITY
SUBTOPIC :11.1 IMMUNE RESPONSE
LEARNING OUTCOMES: (a) Define immunity and state the types of immunity
(b) Describe the general structure of antibodies and state the classes based on its
structure.
(c) State the roles of lymphoid organs in immunity such as:
i. Thymus
ii. Spleen
iii. Tonsil
iv. Lymph nodes
v. Bone marrow
(d) Explain the various types of antigen and antibody interactions:
i. neutralization
ii. opsonization
iii. activation of complement system and pore formation.
MAIN IDEAS
/KEY POINT EXPLANATION NOTES
a. Immunity and
types of
immunity
Immunity:
The ability to recognize and destroy foreign or dangerous macromolecules
(Solomon 10th Ed, 2015).
The state of having sufficient biological defenses to avoid infection, disease or
other unwanted biological invasion by foreign organism or other foreign
Humoral response: Antibodies defend against infection in body
fluids.
Cell-mediated response: Cytotoxic cells defend against infection in body
cells.
Pathogens (example: fungi,
bacteria and viruses)
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MAIN IDEAS
/KEY POINT EXPLANATION NOTES
b. General
structure of
antibodies and
classes based on
its structure.
Antibody:
A specific protein (immunoglobulin) that recognizes and binds to specific
antigen which produced by plasma cells.
Structure of antibodies:
Basic shape of antibody
• Y shaped • 4 polypeptide chains:
✓ 2 identical light chains ✓ 2 identical heavy chains
• Linked by disulphide bridge • Each chain contains:
✓ variable region (V) ✓ constant region (C)
• The constant region of heavy chains: ✓ form the base of antibody molecules ✓ determines the way antibody is secreted & how it is distributed in
body fluid
✓ Eg: circulate in body fluid or bind to membranes of mast cells (mast
cells are cells found in connective tissue that store histamine,
inflammatory signaling molecule)
• The variable region of the light and heavy chain: ✓ determine the specificity of an antibody molecules ✓ amino acid sequence varies extensively from one B cell to another. ✓ part of heavy-chain V region and a light-chain V region form as
asymmetric binding site for an antigen.
• Each antibody has 2 antigen-binding sites ✓ Form by the free tips end of both variable region
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MAIN IDEAS
/KEY POINT EXPLANATION NOTES
Classes of antibody:
i. IgD
• Found in blood and lymph and on surfaces of B cells • Single monomer • Function: act as antigen receptors on the surfaces of
B cells ✓ Stimulating the differentiation of B cells into
plasma cells and memory cells ii. IgE
• Bind to mast cells and basophil and stimulate them
to produce histamines • Single monomer • Function: responsible for allergic reaction but useful
against parasitic worms
iii. IgG
• Temporary protection to newborn. • single monomer • Easily cross the walls of blood vessel and enter tissue
fluid • e.g.: maternal IgG antibodies can cross the placenta
and confer passive immunity to fetus
iv. IgM
• Primary antibody response. • Pentamer: ✓ Large size ✓ 5 monomers held together by
polypeptide called J (joining) chain • First antibodies to appear in response to initial
exposure to an antigen
v. IgA
• Common in mucous membranes and in
body secretions: mucus, saliva, tears, breast
milk • Most abundant in body (IgG most abundant
in serum) • Dimer: 2 monomers held by J chain • Functions: prevent the attachment of
pathogens to mucosal surfaces
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MAIN IDEAS
/KEY POINT EXPLANATION NOTES
c. Roles of
lymphoid
organs in
immunity:
i. Thymus
ii. Spleen
iii. Tonsil
iv. Lymph
nodes
v. Bone
marrow
i. Thymus
• Gland that produces several hormones that are important in developing
& maintaining immune defenses ✓ e.g.: thymosin - promotes the development and maturation of
lymphocyte • Function: Site where the lymphocyte cells mature ✓ Lymphoid stem cells migrate to the thymus ✓ Subsequent divisions produce daughter cells that mature into T
cells
ii. Spleen
• Contains lymphocytes and macrophages • Functions: ✓ Remove abnormal blood cells & other components by phagocytosis ✓ Store iron recycled from erythrocytes ✓ Initiate immune responses by B cells and T cells in response
to antigens in circulating blood
iii. Tonsil
• Large lymphoid nodules in the walls of pharynx • Functions: ✓ Trap bacteria and viruses which were breathe in ✓ Antibodies and immune cells kill the pathogen ✓ Prevents infections in the lung and throat
iv. Lymph nodes
• Small lymphoid organs • Greatest number: neck, armpit, groin • Function: filter and purifies lymph before it reaches the veins
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MAIN IDEAS
/KEY POINT EXPLANATION NOTES
v. Bone marrow
• Site of origin of all types of blood cells • Hemocytoblasts in bone marrow divide to form ✓ myeloid stem cells and ✓ lymphoid stem cells
• Myeloid stem cells divide to form: erythrocyte, platelets, granulocytes,
monocytes
• Lymphoid stem cells divide to form lymphocytes
d. Various types
of antigen and
antibody
interactions:
i. neutralization
ii. opsonization
iii. activation of
complement
system and
pore
formation
Antigen:
• Any foreign molecule that elicits an immune response by binding to
receptors of B cells or T cells. • Usually protein, glycoprotein or polysaccharide • Epitope/antigenic determinant sites: a small, accessible region of an
antigen to which an antigen receptor or antibody binds • An antigen may have several different epitopes • Each epitope is recognized by a different antibody • Different antibodies can recognize distinct epitopes on the same antigen
Antigen and antibody interactions:
• An antigen-antibody complex forms when an antibody molecule binds to
its corresponding antigen molecule • Once the two molecules are in position, hydrogen bonding and other weak
chemical forces lock them together • Antigen covered with antibodies attract eosinophils, neutrophils and
macrophages • These cells then phagocytize the pathogens
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MAIN IDEAS
/KEY POINT EXPLANATION NOTES
i. Neutralization
• A process in which antibodies bind to
proteins on the surface of a virus. • Viruses and bacterial toxins have
specific sites that must bind to target
regions on body cells before they can
enter or injure those cells. • Antibodies bind to those sites, making
the virus or toxin incapable of attaching
itself to cell. • Thus, neutralizing the virus/toxins.
ii. Opsonization
• A process by which a particulate antigen becomes more susceptible to
phagocytosis by macrophages and
neutrophils. • A coating of antibodies and
complement proteins increase the
effectiveness of phagocytosis. • Some bacteria have slick plasma
membranes or capsules, but
opsonization makes it easier for
phagocytes to hang on onto their prey
before they engulf it. • Phagocytes can bind more easily to antibodies and complement
proteins than they can to the bare surface of a pathogen.
iii. Activation of complement system and pore formation
• When an antibody molecule binds to an antigen, it forms antigen-
antibody complex. • Portion of the antibody change shape exposing areas that bind
complement protein. • This binding activates the complement system. • The activated bound complement molecule then forms membrane
attack complex. • Pores formed in plasma membrane, allowing water and ions to rush in. • The cell swells and lyses, destroy the pathogen.
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SUBTOPIC: 11.2 DEVELOPMENT OF IMMUNITY
LEARNING OUTCOMES: (a) State the two types of immune response.
(b) Explain humoral and cell mediated immune response against infection.
(c) Explain the primary and secondary immune responses.
MAIN IDEAS
/KEY POINT EXPLANATION NOTES
a. Two types
of immune
response.
Types of immune response:
i. Humoral immune response The branch of adaptive immunity that involves the activation of B cells and
that leads to the production of antibodies, which defend against bacteria and
viruses in body fluids.
ii. Cell mediated immune response The branch of adaptive immunity that involves the activation of cytotoxic
T cells, which defend against infected cells.
b. Humoral
and cell
mediated
immune
response
against
infection.
Components of humoral and cell mediated immune response:
i. Lymphocytes
Account for 20 – 30 % of circulating leukocytes
(a) B cells
Make up 10-15% of circulating lymphocytes
• Plasma cells ✓ when stimulated, B cells can differentiate into plasma cells
which produce and secrete antibodies
• Memory B cells ✓ Subset of B cells that respond to a previously encountered antigen
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MAIN IDEAS
/KEY POINT EXPLANATION NOTES
(b) T cells
Approximately 80% of circulating lymphocytes are classified as T
cells
• Cytotoxic T cells ✓ Attack foreign cells or body cells infected by viruses.
• Helper T cells ✓ Stimulate the activation and function of both T cells and B
cells. • Suppressor T cells ✓ Inhibit the activation and function of both T and B cells.
• Memory T cells ✓ Subset of T cells that respond to a previously encountered
antigen
ii. Major histocompatibility complex (MHC) molecule
A host protein that functions in antigen presentation.
• Glycoprotein and antigen that appears in plasma membrane is capable
to activate T cells. • Membrane glycoproteins are called MHC proteins/human leukocyte
antigens (HLAs). • Amino acid sequences and shapes of MHC proteins differs among
individuals. • For T cell to recognize an antigen, the antigen must be bound to
glycoproteins in the plasma membranes of another cell.
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MAIN IDEAS
/KEY POINT EXPLANATION NOTES
(a) MHC class I molecule
• Present in plasma membrane of all nucleated cell • Pick up small peptides from the surrounding cytoplasm and carry
them to the cell surface • If the cytoplasm contains abnormal peptides or viral proteins, they
soon appear in the plasma membrane • T cells will recognize them as foreign and be activated
(b) MHC class II molecule
• Present only in the plasma membranes of antigen presenting cell
(APC) and lymphocytes • APCs are specialized cells responsible for activating T cell defenses
against foreign cells (including bacteria) and foreign proteins
iii. Cytokines
Signaling proteins that regulate interaction between cells in the immune
system
(a) Interleukin I (IL-1)
• Primary source: macrophages • Activates helper T cells
(b) Interleukin 2 (IL-2)
• Source: Helper T cells. • Activates B cells and cytotoxic T cells
Helper T (TH) cells stimulate the humoral and cell-mediated immune
response
1. The macrophage ingest a microbe or other foreign particle and breaks it
into fragments (foreign antigens)
2. MHC class II (self protein) bind to foreign antigens
3. Display them on the cell surface
4. Helper T cell recognize and bind to the MHC-antigen complex caused
APC release IL-1; and diffuse to the TH cell and stimulate it.
5. Activated TH cell release IL-2. IL-2 makes TH cell itself grow and divide
producing memory cells and additional active TH cells.
6. IL-2 activate B cells and stimulating the humoral immune response