1. 2018 Biology2
Chapter 24. Immune system

3. NONSPECIFIC DEFENSES AGAINST INFECTION
24.1 Both invertebrates and vertebrates have innate defense against infection
The body’s first lines of defense against infection are nonspecific  innate immunity
Innate immunity does not distinguish one infectious microbe from another
It acts the same whether or not an invader has been previously encountered

4. Nonspecific defensive cells (pattern recognition receptor)
Phagocytes: neutrophil, macrophage ( monocyte) Eat bacteria and viruses in infected tissues
Natural killer cell : attack virus-infected body cells and cancer cells
Pathogen-associated molecular patterns
LPS
Nucleic acids
Flagellin
Peptidoglycan
Lipoteichoic acid
Etc.

5. Interferon
- Produced by virus-infected cells
- Help other neighboring cells resist viruses

6. Complement proteins
- Present in inactive form in the blood plasma
Opsonization: some of these proteins coat the surfaces of microbes, making them easier for macrophages to engulf
Cell lysis: they cut lethal holes in microbial membranes
They amplify the inflammatory response by
promotion of histamine release and
attraction of phagocytes

7. 24.2 The inflammatory response mobilizes innate defences
Tissue damage triggers the inflammatory response
Mast cell + macrophage

8. The inflammatory response can
disinfect tissues
limit further infection
Pus : it is composed of dead cells (neutrophils and the damaged body cells) and leaked fluid

9. 24.3 The lymphatic system becomes a crucial battleground during infection
The lymphatic system is a network of lymphatic vessels and organs
It returns tissue fluid to the circulatory system
It fights infections
Lymphatic organs: lymph node, spleen, appendix, tonsil, adenoid, thymus, bone marrow
Lymphatic vessels have the valve

12. This lymphatic vessel is taking up fluid from tissue spaces
It will return it as lymph to the blood through the thoracic duct and the right lymphatic duct
Lymph contains less oxygen and fewer nutrients than interstitial fluid

13. Lymph nodes are key sites for lymphocyte activation
They are packed with lymphocytes and macrophages
Masses of lymphocytes and
macrophages
Outer capsule of lymph node
Macrophages
Lymphocytes

14. 24.4 The acquired immune response counters specific invaders
Acquired IMMUNITY
24.4 The acquired immune response counters specific invaders
Acquired immune system
Nonspecific defense 통과
Antibody
Cytotoxic T cell
Infectious
agent

15. Antigen: a molecule that elicits an immune response
Antibody: a protein found in blood plasma that attaches to one particular kind of antigen and helps counter its effect
Acquired Immunity: resistance to specific invaders
The acquired immune system is very specific to an antigen
The acquired immune system has a “memory”
The acquired immune system can distinguish between self and nonself
Natural infection Vaccination

16. 24.5 Lymphocytes mount a dual defense
Two kinds of lymphocytes carry out the immune response
B cells secrete antibodies that attack antigens
T cells attack cells infected with pathogens
Figure 24.5

17. Lymphocyte
Produce the immune response
Spend most of their time in the tissues and lymphatic organs
B cell: secrete antibodies  humoral immunity
T cell:
Cytotoxic T cell: attack body cells that have been infected with bacteria or viruses as well as cancer cells  cell-mediated immunity
Helper T cell: promote phagocytosis by other WBC
stimulate B and other T cells

18. Lymphocyte origin: bone marrow
Lymphocyte origin: bone marrow. In some mammals lymphocytes originate in the spleen
Lymphocyte maturation: thymus and bone marrow
Lymphocyte activation: lymphocytes recognize antigens and become activated in the spleen and lymph nodes
Lymphocyte transport: lymphocytes circulate through the circulatory and lymphatic systems.

19. 24.6 Antigens have specific regions where antibodies bind to them
Antigen (Ag)
a molecule that elicits the immune response
Most Ags are protein or large polysaccharides on the surfaces of viruses or foreign cells
Antibody A molecules
Antigen- binding sites
Antigenic determinants
Antigen
Antigenic determinants are the regions to which antibodies bind
Antibody B molecule

20. 24.7 Clonal selection musters defensive forces against specific antigens
When an antigen enters the body, it activates only lymphocytes with complementary receptors
B and T cells multiply into clones of specialized effector cells that defend against the triggering antigen
This is called clonal selection

22. 24.8 The initial immune response results in a type of “memory”
In the primary immune response, clonal selection produces memory cells as well as effector cells
The memory cells may confer lifelong immunity

23. When memory cells are activated by subsequent exposure to an antigen, they mount a more rapid and massive secondary immune response
Unstimulated lymphocyte
First exposure to antigen
FIRST CLONE
Memory cells
Second exposure to antigen
Effector cells
SECOND CLONE
More memory cells
New effector cells

24. 24.9 Overview: B cells are the main warriors of humoral immunity
Triggered by a specific antigen, a B cell differentiates into an effector cell
The effector cell is called a plasma cell
The plasma cell secretes antibodies

25. PRIMARY RESPONSE
(initial encounter
with antigen)
Antigen
Antigen receptor on a B cell
Antigen binding
to a B cell
Cell growth,
division, and
differentiation
Clone of cells
Memory B cell
Plasma cell
Antibody
molecules
Later
exposure
to same
antigen
SECONDARY RESPONSE
(can be years later)
Cell growth,
division, and further
differentiation
Larger clone
of cells
Plasma cell
Memory B cell
Antibody
molecules

26. 24.8 Antibodies are the weapons of humoral immunity
An antibody molecule

27. Each antibody molecule is made up of four polypeptide chains
2 heavy chains + 2 light chains
Disulfide bonds at the fork of the antibody hold these chains together
Each of the four chains of the molecule has a C(constant) region and a V (variable) region
At the tips, a pair of V regions forms an antigen-binding site
The constant regions of the heavy chains help mediate the disposal of the bound antigen
Five classes of antibodies in humans and other mammal
Immunoglobulin G, M, A, E, D (heavy chain의 C region에 따라)

29. Class of Immuno-
globulin (Antibody)
Distribution
Function
IgM
(pentamer)
First Ig class
produced after
initial exposure to
antigen; then its
concentration in
the blood declines
Promotes neutraliza-
tion and cross-
linking of antigens;
very effective in
complement system
activation
J chain

30. Class of Immuno-
globulin (Antibody)
Distribution
Function
IgG
(monomer)
Most abundant Ig
class in blood;
also present in
tissue fluids
Promotes opsoniza-
tion, neutralization,
and cross-linking of
antigens; less effec-
tive in activation of
complement system
than IgM
Only Ig class that
crosses placenta,
thus conferring
passive immunity
on fetus

31. Class of Immuno-
globulin (Antibody)
Distribution
Function
IgA
(dimer)
Present in
secretions such
as tears, saliva,
mucus, and
breast milk
Provides localized
defense of mucous
membranes by
cross-linking and
neutralization of
antigens
J chain
Presence in breast
milk confers
passive immunity
on nursing infant
Secretory
component

32. Class of Immuno-
globulin (Antibody)
Distribution
Function
IgE
(monomer)
Present in blood
at low concen-
trations
Triggers release from
mast cells and
basophils of hista-
mine and other
chemicals that cause
allergic reactions

33. Class of Immuno-
globulin (Antibody)
Distribution
Function
IgD
(monomer)
Present primarily
on surface of
B cells that have
not been exposed
to antigens
Acts as antigen
receptor in the
antigen-stimulated
proliferation and
differentiation of
B cells (clonal
selection)
Trans-
membrane
region

34. 24.9 Antibodies mark antigens for elimination
Antibodies may
block harmful antigens on microbes
clump bacteria or viruses together
precipitate dissolved antigens
activate complement proteins

36. producing monoclonal antibodies
Connection: Monoclonal antibodies are powerful tools in the lab and clinic
These molecules are produced by fusing B cells specific for a single antigenic determinant with easy-to-grow tumor cells
Antigen injected
into mouse
Tumor cells grown
in culture
B cells
(from spleen)
Tumor cells
Cells fused to
generate hybrid
cells
Single hybrid cell
grown in culture
Antibody
Hybrid cell culture,
producing monoclonal antibodies
Figure 24.12A

37. Antigenic determinants
Polyclonal antibodies
Antibody A molecules
Antigen- binding sites
Antigenic determinants
Antigen
Antibody B molecule

38. 24.11 T cells mount the cell-mediated defense and aid humoral immunity
The cell-mediated immunity battles pathogens that have already enter body cells
The antigen alone cannot bind to the T cell receptor on the T cell  The T cell receptor binds to the MHC-Ag complex
Major histocompatibility complex (self protein)
Present the foreign antigens on the cell’s surface
Serve as identity markers for our body cells
Class II MHC (APC), Class I (all nucleated cells)
Antigen-presenting cell : macrophage, B cell, dendritic cell

40. Cell-mediated immunity
Microbe
An antigen-presenting cell (APC) first displays a foreign antigen and one of the body’s own MHC proteins to a helper T cell
Macrophage (will become APC) 1
Antigen from microbe (nonself molecule)
Self protein
Self protein
displaying
antigen
T cell receptor
Binding site for self protein 3 2
Helper
T cell
Class II MHC 4
Binding site
for antigen
APC

41. The helper T cell’s receptors recognize the MHCII-Ag complexes on the APC
The interaction activates the helper T cells
The helper T cell can then activate cytotoxic T cells and B cells with the receptors recognizing the same Ag

44. Class I MHC
Perforin, granzyme, granulysin, Fas ligand

45. In the lymph node
Dendritic cell

46. Dendritic cell

47. Cytotoxic T cells may help prevent cancer
Cytotoxic T cells may attack cancer cells
The surface molecules of cancer cells are altered by the disease
Figure 24.14

48. Active immunity
Passive immunity
Self-tolerance

49. 24.15 The immune system depends on our molecular fingerprints
The immune system normally reacts only against nonself substances
It generally rejects transplanted organs
The cells of transplanted organs lack the recipient’s unique “fingerprint” of MHCs

50. DISORDERS OF THE IMMUNE SYSTEM
Connection: Malfunction or failure of the immune system causes disease
Autoimmune diseases
The system turns against the body’s own molecules
e.g., Rheumatoid arthritis, insulin-dependent diabetes (type I), multiple sclerosis
Immunodeficiency diseases
Immune components are lacking, and infections recur
e.g., severe combined immunodeficiency
Physical and emotional stress may weaken the immune system

51. 24.17 Connection: Allergies are overreactions to certain environmental antigens
Allergies are abnormal sensitivities to allergens in the surroundings
Antihistamine, glucocorticoid, Anaphylactic shock
basophil
Excess production of IgE

52. Connection: AIDS leaves the body defenseless
The AIDS virus attacks helper T Cells
This cripples both cell-mediated and humoral immunity
So far, AIDS is incurable
Drugs and vaccines offer hope for the future
Practicing safer sex could save many lives