1. The Immune System
Chapter 43 ~

2. Lines of Defense
Nonspecific Defense Mechanisms……

3. PCA:
List the organs involved in the immune sytem:

4. Innate Immunity: Specialized phagocytic white blood cells
Antimicrobial proteins
Inflammatory response

5. Innate Immunity: 5 types of Leukocytes
Neutrophils
60-70% WBCs; engulf and destroy microbes at infected tissue
Short lived
Monocytes
5% WBCs; develop into….
Macrophages 1)phagocytosis
2)lysosomal enzymes destroy microbes
Dendritic cells:
Stimulate development of the acquired immune system

6. Innate Immunity: 5 types of Leukocytes
Eosinophils
1.5% WBCs; destroy large parasitic invaders
Enzymatic action- no phagocytosis
Natural killer (NK) cells
destroy virus-infected body cells & abnormal cells
apoptosis

7. Antimicrobial Proteins:
Complement system- group of 30 proteins
Once activated can cause invading cells to lyse – burst
Interferons (α, β and γ)
Immune response to viruses
Activates macrophages

8. The Inflammatory Response
Tissue injury; release of chemical signals~ • histamine (basophils/mast cells): causes Step • prostaglandins: increases blood flow & vessel permeability
Dilation and increased permeability of capillary~
chemokines: secreted by blood vessel endothelial cells mediates phagocytotic migration of WBCs
Phagocytosis of pathogens~
• fever: leukocyte-released molecules increase body temperature

10. Acquired Immunity:
Lymphocyctes •pluripotent stem cells... • B Cells (bone marrow) • T Cells (thymus)
Antigen: a foreign molecule that elicits a response by lymphocytes (virus, bacteria, fungus, protozoa, parasitic worms)
Antibodies: antigen-binding immunoglobulin, produced by B cells
Antigen receptors: plasma membrane receptors on B and T cells

11. Acquired Immunity: Epitope- antigenic determinant
Small area on antigen recognize by lymphcyte

12. T cell receptors and MHC:
Major Histocompatibility Complex (MHC)
Antigen presentation- bind to fragments and bring them towards the cell surface
Two classes:
Class I MHC
Class II MHC

13. MHC
Class I MHC(nucleated body cells): recognizes antigen fragments in the cell, binds to them and displays them at the cell surface
Cytotoxic T cells will bind and destroy fragments
Class II MHC: recognizes antigen fragments in the cell, binds to them and displays them at the cell surface
Helper T cells will bind and initiate a process to destroy fragments

15. Cytotoxic T cell mechanism
Destroy cells infected by intracellular pathogens and cancer cells
Activity enhanced by CD8 surface protein present on most cytotoxic T cells (similar to CD4 and class II MHC)
cell lysis and pathogen exposure to circulating antibodies

16. Cytotoxic T cell mechanism:
the activated cytotoxic T cells release:
perforins which form pores in the target cell membrane
and proteolytic enzymes which enter the cell via endocytosis and initiate apoptosis
Cytotoxic T cell becomes first activated by the secretion of cytokines from helper T cells

17. Cytotoxic T cell mechanism

18. Helper T cell mechanism:
Function in both humoral & cell-mediated immunity
Stimulated by antigen presenting cells
T cell surface protein CD4 enhances activation(similar to CD8 of class II MHC)
Cytokines secreted (stimulate other lymphocytes):
a) interleukin-2 (IL-2): activates B cells and cytotoxic T cells
b) interleukin-1 (IL-1): activates helper T cell to produce IL-2

19. Helper T cell mechanism:
a helper T cell recognizes the complex becomes activated with the aid of cytokines secreted by the macrophage forming a clone of activated helper T cells
an activated T cell binds to the B cell
B cell becomes activated with the help of cytokines

20. Helper T cell mechanism

21. Clonal Selection:
1. antigen binds to antigen receptors of a specific lymphocyte
2. the selected lymphocyte proliferates forming a clone of identical cells bearing the same receptors
3. some of the proliferated cells develop into short- lived effector cell(plasma cell if B lymphocyte, helper T cell or cytotoxic T cell if T lymphocyte) that secrete antibodies specific for the antigen or destroy the antigen
4. some proliferated cells develop into long lived memory cells that can respond rapidly upon exposure of the same antigen

22. Clonal Selection

23. Induction of Immune Responses
primary immune response- the selective proliferation and differentiation of lymphocytes that occur the first time the body is exposed to a particular antigen (10-17 days)
secondary immune response- if individual is exposed again to the same antigen, the response is faster( 2- 7 days)- immunological memory

24. Induction of Immune Responses

25. Types of immune responses
Cell-mediated immunity
T cell activation
Binds to and/or lyses cells
Defend against intracellular pathogens such as bacteria, viruses, fungi, protozoa, and parasite s; and cancer cells
Humoral immunity
B cell activation
Production of antibodies
Defend against bacteria, toxins, and viruses free in the lymph and blood plasma

26. Humoral response: B cells
Stimulated by T-dependent antigens (help from TH cells)
Macrophage (APCs) with class II MHC proteins
Helper T cell (CD4 protein)
Activated T cell secretes IL-2 (cytokines) that activate B cell
B cell differentiates into memory and plasma cells (antibodies)

27. Antibody Structure & Function
Epitope: region on antigen surface recognized by antibodies
2 heavy chains and 2 light chains joined by disulfide bridges
Antigen-binding site (variable region)

28. 5 classes of Immunoglobins
IgM: 1st to circulate; indicates infection; too large to cross placenta
IgG: most abundant; crosses walls of blood vessels and placenta; protects against bacteria, viruses, & toxins; activates complement
IgA: produced by cells in mucous membranes; prevent attachment of viruses/bacteria to epithelial surfaces; also found in saliva, tears, and perspiration
IgD: do not activate complement and cannot cross placenta; found on surfaces of B cells; probably help differentiation of B cells into plasma and memory cells
IgE: very large; small quantity; releases histamines-allergic reaction

29. Antibody-mediated Antigen Disposal
Opsonization: antibody binds to and blocks antigen activity-coats antigen surface enhancing macrophage activity
Agglutination: antigen clumping- antibodies contain at least two antigen binding sites
Precipitation: cross-linking of soluble antigens- forms immobile aggregates that are disposed of by phagocytosis
Viral Neutralization: antibodies bind to certain proteins on the surface of a virus blocking its ability to infect a host cell

30. Immunity in Health & Disease
Active immunity
natural: conferred immunity by recovering from disease
artificial: immunization and vaccination; produces a primary response
Passive immunity: transfer of immunity from one individual to another
natural: mother to fetus; breast milk
artificial: rabies
Transfer of antibodies from rabid(immune) animal to non-rabid (non-immune) animal

31. Self/Nonself Recognition
Self-tolerance: capacity to distinguish self from non-self
Autoimmune diseases: failure of self-tolerance; multiple sclerosis, lupus, rheumatoid arthritis, insulin-dependent diabetes mellitus

32. Blood Group and Transfusions:
See PCA: Explain why blood type AB is considered the universal recipient and blood type O is considered the universal donor?

33. Abnormal immune function
Allergies (anaphylactic shock): hypersensitive responses to environmental antigens (allergens); causes dilation and blood vessel permeability
Allergy symptoms can be diminished with antihistamines
The hormone epinephrine counter acts this allergic reaction
Autoimmune disease:
Immunodeficiency disease: SCIDS (bubble-boy); A.I.D.S.

35. Essay: 10pts.
1. Describe the main role of the following cells types: helper T cells, cytotoxic T cells and B cells.
2. What is responsible for the activation of these molecules?
3. What deficiencies, if any would result from an individual born without a Thymus?