1. 2.D.4 Immune System & Our Chemical Defenses
Animals (& plants) have a variety of chemical defenses against infections that affect dynamic homeostasis.

2. (Acquired or Adaptive Response)
Immune System
Nonspecific Response
(Innate Response)
Plants
Invertebrates
Vertebrates
Specific Response
(Acquired or Adaptive Response)
Vertebrates Only

3. A pathogen is  a biological agent such as a virus, bacterium, prion, or fungus, that causes a disease or infection in its host.

4. Plants, invertebrates and vertebrates have multiple, nonspecific immune responses to pathogens.

5. Example: Invertebrate immune systems lack pathogen-specific defense responses. Innate immunity in invertebrates consists of the exoskeleton and the digestive system and its associated microorganisms.

6. Immune cells called hemocytes are found inside the hemolypmh of insects. They engulf pathogens via phagocytosis .

7. (Acquired or Adaptive Response)
Vertebrate immune systems have specific and nonspecific defense mechanisms against pathogens.
Immune System
Nonspecific Response
(Innate Response)
Specific Response
(Acquired or Adaptive Response)

8. Nonspecific immunity, or innate immunity, is present before any exposure to pathogens and is effective from the time of birth.

9. Innate immunity provides broad defenses against infection
Innate immunity provides broad defenses against infection. A pathogen that successfully breaks through an animal’s external defenses soon encounters several innate cellular and chemical mechanisms that impede its attack on the body.
3m

10. Intact skin and mucous membranes form physical barriers that bar the entry of microorganisms and viruses. Certain cells of the mucous membranes produce mucus, a viscous fluid that traps microbes and other particles.

11. In the trachea, ciliated epithelial cells sweep mucus and any entrapped microbes upward, preventing the microbes from entering the lungs.

12. Secretions of the skin and mucous membranes provide an environment that is often hostile to microbes. The skin has a pH between 3 and 5, which is acidic enough to prevent colonization of many microbes. Also, lysozymes are enzymes abundant in a number of secretions, such as tears, saliva, human milk, and mucus that break down the cell walls of many bacteria.

13. Internal cellular and chemical defenses depend mainly on phagocytosis
Internal cellular and chemical defenses depend mainly on phagocytosis. Phagocytes are types of white blood cells that ingest invading microorganisms and initiate the inflammatory response.

14. Macrophages, a specific type of phagocyte, can be found migrating through the body and in various organs of the lymphatic system.

15. Phagocytes such as macrophages attach to their prey via surface receptors and engulf them, forming a vacuole that fuses with a lysosome.

16. Numerous antimicrobial proteins function in innate defense by attacking microbes directly of by impeding their reproduction. They have been demonstrated to kill Gram negative and Gram positive bacteria, mycobacteria, enveloped viruses, fungi, and even transformed or cancerous cells.

17. About 30 antimicrobial proteins make up the complement system
About 30 antimicrobial proteins make up the complement system. The complement system can cause lysis of invading cells and help trigger inflammation.
Interferons (IFNs) provide innate defense against viruses and help activate macrophages.

18. Inflammatory Response
In local inflammation, histamine and other chemicals released from injured cells promote changes in blood vessels that allow more fluid, more phagocytes, and antimicrobial proteins to enter the tissues.

19. Inflammatory Response
Neutrophils and monocytes migrate to the site of injury
Neutrophils and mast cells phagocytize pathogens
Monocytes differentiate into macrophages

20. Natural killer (NK) cells patrol the body and attack virus-infected body cells and cancer cells. They trigger apoptosis in the cells they attack.

21. (Acquired or Adaptive Response)
Immune System
Nonspecific Response
(Innate Response)
Physical barriers such as skin, mucus membranes, cilia, sweat, saliva, stomach acid
Complement System Proteins
Macrophages
Natural Killer (NK) Cells
Inflammatory Response
Specific Response
(Acquired or Adaptive Response)

22. (Acquired or Adaptive Response)
Specific immunity, also called acquired immunity or adaptive immunity, develops only after exposure to inducing agents such as microbes, toxins, or other foreign substances.
Immune System
Nonspecific Response
(Innate Response)
Specific Response
(Acquired or Adaptive Response)

23. Consists of lymphatic vessels and the lymphoid organs
Lymph nodes - Red bone marrow (B-Cells) - Thymus gland (T-Cells) - Lymphatic vessels – Tonsils – Spleen

24. In acquired immunity, lymphocytes (white blood cells) provide specific defenses against infection.

25. Lymphocytes arise from stem cells in the bone marrow.

26. B cells mature in the Bone marrow. T cells mature in the Thymus.
Lymphoid
stem cell
B cell
Blood, lymph, and lymphoid tissues
(lymph nodes, spleen, and others)
T cell
Thymus

27. An antigen is any foreign molecule that is specifically recognized by lymphocytes and elicits a response from them. A lymphocyte recognizes and binds to just a small, accessible portion of the antigen called an epitope.
Antigen-
binding
sites
Antibody A
Antigen
Antibody B
Antibody C
Epitopes
(antigenic
determinants)

28. Vertebrates have two types of specific immune responses: cell mediated immunity and humoral immunity.
Specific (Acquired or Adaptive) Immune Response
Cell Mediated Immunity
Humoral Immunity

29. The vertebrate body is populated by two main types of lymphocytes which circulate through the blood:
B lymphocytes (B cells)
T lymphocytes (T cells)
Specific (Acquired or Adaptive) Immune Response
Cell Mediated Immunity
T Cells
Humoral Immunity
B Cells

30. The plasma membranes of both B cells and T cells have about 100,000 antigen receptors that all recognize the same epitope.

31. B cell receptors bind to specific, intact antigens
B cell receptors bind to specific, intact antigens. They are often called membrane antibodies or membrane immunoglobulins.
Antigen-
binding
site
binding site
Disulfide
bridge
Light
chain
Heavy chains
Cytoplasm of B cell V
A B cell receptor consists of two identical heavy
chains and two identical light chains linked by
several disulfide bridges.
(a)
Variable
regions
Constant
Transmembrane
region
Plasma
membrane
B cell C

32. Each T cell receptor consists of two different polypeptide chains.
Antigen-
Binding site
b chain
Disulfide bridge
a chain
T cell
A T cell receptor consists of one
chain and one b chain linked by
a disulfide bridge.
(b)
Variable
regions
Constant
Transmembrane
region
Plasma
membrane
Cytoplasm of T cell V V C C

33. T cells bind to small fragments of antigens that are bound to normal cell-surface proteins called MHC molecules. MHC molecules are encoded by a family of genes called the major histocompatibility complex.

34. Infected cells produce MHC molecules which bind to antigen fragments and then are transported to the cell surface in a process called antigen presentation. A nearby T cell can then detect the antigen fragment displayed on the cell’s surface.

35. Depending on their source peptide, antigens are handled by different classes of MHC molecules.

36. Class I MHC molecules, found on almost all nucleated cells of the body, display peptide antigens to cytotoxic T cells.
Infected cell
Antigen
fragment
Class I MHC
molecule
T cell
receptor
(a) Cytotoxic T cell
A fragment of
foreign protein
(antigen) inside the
cell associates with
an MHC molecule
and is transported
to the cell surface. 1
The combination of
MHC molecule and
antigen is recognized
by a T cell, alerting it
to the infection. 2 1 2

37. Class II MHC molecules, located mainly on dendritic cells, macrophages, and B cells, display antigens to helper T cells.
Microbe
Antigen-
presenting
cell
Antigen
fragment
Class II MHC
molecule
T cell
receptor
Helper T cell
A fragment of
foreign protein
(antigen) inside the
cell associates with
an MHC molecule
and is transported
to the cell surface. 1
The combination of
MHC molecule and
antigen is recognized
by a T cell, alerting it
to the infection. 2
(b) 1 2

38. As B and T cells are maturing in the bone and thymus, their antigen receptors are tested for possible self-reactivity. Lymphocytes bearing receptors for antigens already present in the body are destroyed by apoptosis or rendered nonfunctional.

39. Humoral and cell-mediated immunity defend against different types of threats. Acquired immunity includes two branches:
Specific (Acquired or Adaptive) Immune Response
Cell Mediated Immunity
T Cells
Humoral Immunity
B Cells
• The humoral immune response (B Cells) • The cell-mediated immune response (T Cells)

40. • The humoral immune response involves the activation and clonal selection of B cells, resulting in the production of secreted antibodies. • The cell-mediated immune response involves the activation and clonal selection of cytotoxic T cells .
Specific (Acquired or Adaptive) Immune Response
Cell Mediated Immunity
T Cells
Cytotoxic T Cells
Humoral Immunity
B Cells
Antibodies

42. Cell Mediated Response

43. Helper T cells produce CD4, a surface protein that enhances their binding to class II MHC molecule–antigen complexes on antigen-presenting cells. Activation of the helper T cell then occurs.

44. Activated helper T cells secrete several different cytokines that stimulate other lymphocytes.

45. The activated cytotoxic T cell secretes proteins that destroy the infected target cell
Perforin
Granzymes
CD8
TCR
Class I MHC
molecule
Target
cell
Peptide
antigen
Pore
Released
cytotoxic
T cell
Apoptotic
target cell
Cancer
Cytotoxic
A cytotoxic T cell binds to a
class I MHC–antigen complex on a
target cell with the aid of
CD8. This interaction, along with
cytokines from helper T cells, leads to
the activation of the cytotoxic cell. 1
The activated T cell releases perforin
molecules, which form pores in the
target cell membrane, and proteolytic
enzymes, which enter the
target cell by endocytosis. 2
The enzymes initiate apoptosis within the
target cells, leading to fragmentation of the
nucleus, release of small apoptotic bodies,
and eventual cell death. The released
cytotoxic T cell can attack other target cells. 3

46. Humoral Response

47. Activation of B cells is aided by cytokines and antigen binding to helper T cells.

49. An antibody, also known as an immunoglobulin (Ig), is a large Y-shaped protein produced by B-cells that is used by the immune system to identify and neutralize pathogens.

50. Each antibody is specific to a particular antigen
Each antibody is specific to a particular antigen. Each tip of the "Y" of an antibody contains a paratope that is specific for one particular epitope on an antigen, allowing these two structures to bind together with precision. 

51. The binding of antibodies to antigens is also the basis of several antigen disposal mechanisms. It further leads to elimination of microbes by phagocytosis and complement-mediated lysis.

52. Antibody-mediated mechanisms of antigen disposal:
Binding of antibodies to antigens
inactivates antigens by
Viral neutralization
(blocks binding to host)
and opsonization (increases
phagocytosis)
Agglutination of
antigen-bearing particles,
such as microbes
Precipitation of
soluble antigens
Activation of complement system
and pore formation
Bacterium
Virus
Bacteria
Soluble
antigens
Foreign cell
Complement
proteins
MAC
Pore
Enhances
Phagocytosis
Leads to
Cell lysis
Macrophage

53. A primary immune response is the response that occurs after a harmful antigen has been encountered for the first time.

54. In a primary immune response, the binding of an antigen to a mature lymphocyte induces the lymphocyte’s proliferation and differentiation, a process called clonal selection.

55. Clonal selection of B cells generates a clone of short-lived activated effector cells and a clone of long-lived memory cells.
Antigen molecules
Antigen
receptor
B cells that
differ in
antigen
specificity
Antibody
molecules
Clone of memory cells
Clone of plasma cells
bind to the antigen
receptors of only one
of the three B cells
shown.
The selected B cell
proliferates, forming
a clone of identical
cells bearing
receptors for the
selecting antigen.
Some proliferating
cells develop into
short-lived plasma
cells that secrete
antibodies specific
for the antigen.
Some proliferating cells
develop into long-lived
memory cells that can
respond rapidly upon
subsequent exposure
to the same antigen.

56. The secondary immune response is a much quicker and more effective response that occurs after a previously encountered antigen reappears.

57. Antibody concentration
In the secondary immune response, memory cells facilitate a faster, more efficient response.
Antibody concentration
(arbitrary units)
104
103
102
101
100 7 14 21 28 35 42 49 56
Time (days)
Antibodies
to A
to B
Primary
response to
antigen A
produces anti-
bodies to A 2
Day 1: First
exposure to 1
Day 28:
Second exposure
to antigen A; first
antigen B 3
Secondary response to anti-
gen A produces antibodies
to A; primary response to anti-
gen B produces antibodies to B 4

58. Immunization 1. Vaccines provide antigen to which immune system responds 2. Pathogens or pathogen products treated to remove virulence

59. Passive Immunity
Occurs when an individual is given prepared antibodies (immunoglobins) to combat a disease
-Short-lived
-Newborns are
often passively
immune due to
mother’s blood &
milk

60. Immunity Side Effects Tissue Rejection Autoimmune Diseases
Antibodies and cytotoxic T cells bring about destruction of foreign tissues in the body
Immune system is correctly distinguishing between self and nonself
Autoimmune Diseases
Cytotoxic T cells or antibodies mistakenly attack the body’s own cells

61. Autoimmune Diseases result as an attack on tissues by body’s own antibodies and T cells. It is the bodies INABILITY to distinguish self from non-self.  

62. Type 1 Diabetes: an autoimmune disease that results in the destruction of insulin-producing cells of the pancreas.

63. Type 2 Diabetes: diet-related insulin resistance brought on by too much sugar in the diet and lack of exercise.

64. Autoimmune Diseases
Lupus - a chronic inflammatory disease that occurs when your body's immune system attacks your own tissues and organs
There are no cures for autoimmune diseases but they are controlled by drugs

65. broad range of microbes
A summary of innate and acquired immunity:
INNATE IMMUNITY
Rapid responses to a
broad range of microbes
ACQUIRED IMMUNITY
Slower responses to
specific microbes
External defenses
Internal defenses
Skin
Mucous membranes
Secretions
Phagocytic cells
Antimicrobial proteins
Inflammatory response
Natural killer cells
Humoral response
(antibodies)
Cell-mediated response
(cytotoxic
lymphocytes)
Invading
microbes
(pathogens)

67. Learning Objectives:
LO 2.29 The student can create representations and models to describe immune responses. [See SP 1.1, 1.2]
LO 2.30 The student can create representations or models to describe nonspecific immune defenses in plants and animals.[See SP 1.1, 1.2]