1. Specific Defense Mechanisms – The Immune System

2. The Specific Defense System
3rd Line of Defense
Antigen specific – recognizes and acts against particular foreign substances
Systemic – not restricted to the initial infection site
Has memory – recognizes and mounts a stronger attack on previously encountered pathogens

3. Types of Immunity 1. Humoral immunity Antibody-mediated immunity
Cells produce antibodies for defense found in the fluid (serum)
2. Cellular immunity
Cell-mediated immunity
Lymphocytes target virus infected cells, cancer cells, foreign grafts.

4. Antigens (Nonself)
Any substance capable of exciting the immune system and provoking an immune response
Examples of common antigens
- Foreign proteins
- Nucleic acids
- Large carbohydrates
- Some lipids
- Pollen grains
- Microorganisms

5. Self-Antigens Human cells have many surface proteins
Our immune cells do not attack our own proteins
Our cells in another person’s body can trigger an immune response because they are foreign
- Restricts donors for transplants

6. Allergies
Many small molecules (called haptens or incomplete antigens) are not antigenic, but link up with our own proteins
The immune system may recognize and respond to a protein-hapten combination
The immune response is harmful rather than protective because it attacks our own cells

7. Cells of the Immune System
Lymphocytes
Originate from hemocytoblasts in the red bone marrow
B lymphocytes become immunocompetent in the bone marrow
T lymphocytes become immunocompetent in the thymus
Macrophages
Arise from monocytes
Become widely distributed in lymphoid organs

8. Activation of Lymphocytes

9. Humoral (Antibody-Mediated) Immune Response
B cells w/ specific receptors bind to specific antigen
Binding activates the B-cell to undergo clonal selection
Many clones are produced (1° humoral response)
Most B cells become plasma cells
- Produce antibodies to destroy antigens
- Activity lasts for four or five days
Some B cells become memory cells (2° humoral response)

11. Stem Cells Immature B Cells Activated B Cells Plasma Cells
Bone Marrow
Stem Cells
Formed in bone marrow, become
immunocompetent (appearance of
cell surface antibodies), then migrates
to lymph nodes.
Immature B Cells
Activated B Cells
When comes in contact with
specific antigen they undergo repeated mitosis and form clones.
Remembers subsequent
exposure, then can change
to plasma cells rapidly.
Plasma Cells
Memory Cells
Secretes
Antibodies

12. Humoral Immune Response

17. Secondary Response Memory cells are long-lived
A second exposure causes a rapid response
The secondary response is stronger, faster & longer lasting

18. Active Immunity
When your own immune system encounters antigens and produces antibodies
Active immunity can be naturally or artificially acquired

19. Passive Immunity Antibodies are obtained from someone else
- mother to fetus (placenta or milk)
- Injection of immune serum or gamma globulin
Immunological memory does not occur
Protection provided by “borrowed antibodies”

20. Monoclonal Antibodies
Antibodies prepared for clinical testing or diagnostic services
Produced from descendents of a single cell line
Examples of uses for monoclonal antibodies
- Diagnosis of pregnancy
- Treatment after exposure to hepatitis and rabies

21. Antibodies (Immunoglobulins) (Igs)
Soluble proteins secreted by B cells (plasma cells)
Carried in blood plasma
Capable of binding specifically to an antigen

22. Antibody Structure Four amino acid chains linked by disulfide bonds
Two identical amino acid chains are linked to form a heavy chain
The other two identical chains are light chains
Specific antigen-binding sites are present

23. Antibody Classes
Antibodies of each class have slightly different roles
Five major immunoglobulin classes
IgM – can fix complement
IgA – found mainly in mucus
IgD – important in activation of B cell
IgG – can cross the placental barrier
IgE – involved in allergies

24. Antibody Function Antibodies inactivate antigens in a number of ways
Complement fixation
Neutralization
Agglutination
Precipitation

25. Antibody Function 1 2 3 4

26. Cellular (Cell-Mediated) Immune Response
Development of T Cells
Stem cells from the bone marrow seed the thymus gland, and shortly before and after birth they develop into T cells (lymphocytes).
They leave the thymus and take up residence in lymph nodes.

27. They have specific antibody molecules that fit one specific antigen embedded in its plasma membrane.
The second stage of development occurs when the T cell comes in contact with its specific antigen…(antigen presentation by macrophage).

28. Cellular (Cell-Mediated) Immune Response

29. …when this happens the T cell changes into a sensitized T cell.
Produces cell-mediated immunity (resistance to disease organisms resulting from the action of cells).
After antigen binding, clones form as with B cells, but different classes of cells are produced

30. T Cell Clones Cytotoxic T cells Specialize in killing infected cells
Insert a toxic chemical (perforin)
Helper T cells
Recruit other cells to fight the invaders
Interact directly with B cells
PRESS
TO PLAY
CYTOTOXIC T CELLS ANIMATION
PRESS
TO PLAY
HELPER T CELLS ANIMATION

31. T Cell Clones Suppressor T cells
Release chemicals to suppress the activity of T and B cells
Stop the immune response to prevent uncontrolled activity
A few members of each clone are memory cells

32. Summary of the Immune Response
Figure 12.19

37. Organ Transplants and Rejection
Major types of grafts
Autografts – tissue transplanted from one site to another on the same person
Isografts – tissue grafts from an identical person (identical twin)
Allografts – tissue taken from an unrelated person
Xenografts – tissue taken from a different animal species

38. Organ Transplants and Rejection
Autografts and isografts are ideal donors
Xenografts are never successful
Allografts are more successful with a closer tissue match

39. Disorders of Immunity: Allergies (Hypersensitivity)
Abnormal, vigorous immune responses
Types of allergies
Immediate hypersensitivity
Triggered by release of histamine from IgE binding to mast cells
Reactions begin within seconds of contact with allergen
Anaphylactic shock – dangerous, systemic response

40. Allergy Mechanisms
Figure 12.20

41. Disorders of Immunity: Allergies (Hypersensitivity)
Types of allergies (continued)
Delayed hypersensitivity
Triggered by the release of lymphokines (not histamine) from activated helper T cells
Symptoms usually appear 1–3 days after contact with antigen
Common example: allergic contact dermatitis (poison ivy)

42. Disorders of Immunity: Immunodeficiencies
Production or function of immune cells or complement is abnormal
May be congenital (SCID) or acquired (AIDS)
AIDS cripples the immune system by interfering with the activity of helper T cells
Read

43. Disorders of Immunity: Autoimmune Diseases
The immune system does not distinguish between self and nonself
The body produces antibodies and sensitized T lymphocytes that attack its own tissues

44. Disorders of Immunity: Autoimmune Diseases
Examples of autoimmune diseases
Multiple sclerosis – white matter of brain and spinal cord are destroyed
Myasthenia gravis – impairs communication between nerves and skeletal muscles by destroying Ach receptors on muscles.
Juvenile diabetes – destroys pancreatic beta cells that produce insulin
Rheumatoid arthritis – destroys synovial membranes in and near joints

45. Disorders of Immunity: Autoimmune Diseases
Examples of autoimmune diseases (continued)
Systemic lupus erythematosus (SLE) – attacks connective tissue in general. Affects kidney, heart, lung and skin
Glomerulonephritis – impairment of renal function

46. Self Tolerance Breakdown
Inefficient lymphocyte programming
Appearance of self-proteins in the circulation that have not been exposed to the immune system
Eggs
Sperm
Eye lens

47. Self Tolerance Breakdown
Cross-reaction of antibodies produced against foreign antigens with self-antigens
Rheumatic fever

48. Developmental Aspects of the Lymphatic System and Body Defenses
Except for thymus and spleen, the lymphoid organs are poorly developed before birth
A newborn has no functioning lymphocytes at birth; only passive immunity from the mother
If lymphatics are removed or lost, severe edema results, but vessels grow back in time