1. Lecture 22: The Lymphatic System and Immunity
Lecturer: Dr. Barjis
Room P307
Phone: (718)

2. Learning Objectives
Describe the structure and function of lymphatic cells, tissues and organs
List the body’s nonspecific defenses and describe the components and mechanisms of each
Define specific resistance and distinguish between cell-mediated immunity and antibody mediated immunity

3. Learning Objectives
Discuss the role of the T cell, B cell and antibodies in specific immunity
Describe the origin, development, activation and regulation of normal resistance to disease
Discuss the effects of stress and aging on the immune system

4. lymphatic system The lymphatic system
Contains cells, tissues, and organs responsible for defending the body
Lymphocytes resist infection and disease by responding to
Invading pathogens such as bacteria or viruses
Abnormal body cells such as cancer cells
Foreign proteins such as toxins

5. The Components of the Lymphatic System

6. The lymphatic system consists of
Lymphatic vessels
Lymphoid tissues and organs
Lymphocytes and supporting phagocytic cells

7. Functions of lymphatic system
Primary function is production, maintenance, and distribution of lymphocytes
Lymphocytes must:
Detect where problems exist
Be able to reach the site of injury or infection
Return of fluid and solutes from peripheral tissue to blood
Distribution of hormones, nutrients, and waste product from their tissue of origin to general circulation.

8. Lymphatic vessels include
Lymphatic capillaries
Small lymphatic vessels
Major lymph-collecting vessels

9. Lymphatic Capillaries

10. Major lymph-collecting vessels
Superficial and deep lymphatics
Thoracic duct
Cisterna chyli
Right lymphatic duct

11. The Relationship between the Lymphatic Ducts and the Venous System
Most of the lymph returns to the venous circulation by Thoracic duct

12. The Relationship between the Lymphatic Ducts and the Venous System

13. Lymphocytes
Account for % of circulating WBC, but body contain 10 to the power of 12 lymphocytes
There are tree classes of lymphocytes
T (thymus dependent) cells
B (bone marrow-derived) cells
NK (natural killer) cells

14. Lymphocytes Major types of T cells
Cytotoxic T cells (TC) – attack foreign cells
Helper T cells (TH) – activate other T cells and B cells
Suppressor T cells (TS) – inhibit the activation of T and B cells
TH and TS cells regulates immune response

15. Lymphocytes Major types of B cells Active B cell differentiates into
Memory B Cell or
Plasma B cell
Plasma B cells synthesize and release antibody

16. Lymphocyte production (lymphopoiesis)
Lymphocyte production and maturation involves bone marrow, thymus, and peripheral lymphoid tissue
B cells and NK cells mature in bone marrow
T cells mature in the thymus

17. The Derivation and Distribution of Lymphocytes

18. Lymphoid tissue Connective tissue dominated by lymphocytes
Lymphoid nodules
Lymphocytes are packed densely
Found in the respiratory, digestive, and urinary tracts
MALT (mucosa-associated lymphoid tissue)
Collection of lymphoid tissues linked with the digestive system

19. Lymphoid Nodules

20. Lymphoid organs include: lymphoid nodes, thymus and spleen
Lymph nodes – function in the purification of lymph

21. The Thymus Located behind sternum in anterior mediastinum
Reaches its maximum size just before puberty
Consists two lobes
Divided into of lobules, each with a cortex and medulla
Lymphocytes in cortex are dividing, when mature migrate to modula and after 3 weeks enter the blood
Secretes thymic hormones: thymosins, thymopoietins, and thymulin
stimulate stem cell division and T-cell differentiation

22. The Thymus

23. The Spleen Largest mass of lymphoid tissue
Cellular components form pulp
Red pulp contains RBC
White pulp similar to lymphoid nodules
Spleen functions include
Removal of abnormal blood cells and other blood components
Storage of iron
Initiation of the specific immune response

24. The Spleen

25. Lymphatic system and body defenses
Nonspecific defenses
Do not distinguish one type of pathogen (e.g. bacteria) from another type
There are 7 types of non specific defenses
Specific defenses
Protect against one particular threats
Specific defense depend upon the activation of lymphocytes

26. Nonspecific Defenses Physical barriers
Keep hazardous organisms outside the body
Includes hair, epithelia, secretions of integumentary and digestive systems

27. Nonspecific Defenses Phagocytes
Remove cellular debris and respond to invasion by foreign pathogens

28. Immunological surveillance
Nonspecific Defenses
Immunological surveillance
Constant monitoring of normal tissue by NK cells
NK cells
Recognize cell surface markers on foreign cells
Destroy cells with foreign antigens
Activation of NK cells:
Recognition of unusual surface proteins
Rotation of the Golgi toward the target cell and production of perforins
Release of perforins by exocytosis
Interaction of perforins causing cell lysis

29. Nonspecific Defenses
Immunological Surveillance)

30. How Natural Killer Cells Kill Cellular Targets

31. Interferons (cytokines)
Nonspecific Defenses
Interferons (cytokines)
Interferons are small proteins that act as chemical messengers that coordinate defense
Interferons are released by virally infected cells and activated lymphocyytes
Interferons bind to the surface of abnormal cells and trigger the production of antiviral proteins that prevents virus proliferation.

32. Nonspecific Defenses Complement system
There are 11 plasma complement proteins (C)
They are activated by:
Classical pathway
In Classical pathway compliment binds to Ab molecule,
Alternative pathway
In alternative pathway compliment binds to bacterial cell
Both pathways trigger:
Chain of reaction and result attraction of phagocytes,
Stimulation of phagocitic activity,
Promotion of inflammation and
Result puncture of bacterial cell

33. Nonspecific Defenses Inflammation
Localized tissue response to injury producing
Swelling
Redness
Heat
Pain
Effects of inflammation include
Temporary repair of injury
Slowing the spread of pathogens

34. Nonspecific Defenses
Inflammatory Response

35. Nonspecific Defenses Fever
Maintenance of a body temperature above 37.2oC (99oF)
High temperature may inhibit some viruses and bacterial activities.
It increases metabolism (1°C increase in temperature would increase metabolism by 10%)
Pyrogens reset the hypothalamic thermostat and raise body temperature
Pyrogen secretion is stimulated by Ag, macrophages

36. Specific Defenses Act on specific Ag only
T-Cells are responsible for cell mediated immunity (cellular immunity) – defense against abnormal cells and pathogens inside cells
B-cells provide Ab-mediated immunity (also called humoral immunity) – defense against Ags and pathogens in body fluid

37. Specific Defenses Forms of immunity Innate immunity
Genetically determined
Present at birth
Acquired immunity
Not present at birth
Achieved by exposure to antigen
Acquired immunity can be
Active immunity
Passive immunity

38. Types of Immunity

39. Properties/characteristics of immunity
Specificity – activated by and responds to a specific antigen
Versatility – is ready to confront any antigen at any time
Memory – “remembers” any antigen it has encountered
Tolerance – responds to foreign substances but ignores normal tissues

40. The immune system response
Antigen triggers an immune response
Activates T cells and B cells
T cells are activated after phagocytes exposed to antigen
T cells attack the antigen and stimulate B cells
Activated B cells mature and produce antibody
Antibody attacks antigen

41. T cell activation
T cells recognize Ag-glycoprotein complex in cell membrane
Glycoproteins are synthesized in the region called Major Histocompatibility Complex (MHC)- so they are known as MHC proteins
Each individual have different MHC proteins
There are 2 classes of MHC proteins:
MHC class I
MHC class II

42. MHC classes Class I – found on all nucleated cells
They are synthesized, and transported to membrane by vesicles of golgi apparatus
As they are formed, they pick up small peptides from the cytoplasm and take them to membrane
If the peptides that are picked up by MHC proteins are self (belong to the body), T-cells will ignore them,
If the peptides that are picked up by the MHC proteins are none self (do not belong to the body i.e. if they are antigens) then T-cell becomes activated anddestroy the abnormal cell.

43. Antigens and MHC Proteins

44. MHC classes
Class II – found on antigen presenting cells and lymphocytes
Phagocitic cells engulf pathogen
Once the pathogen is inside the phagocitic cell, lysosome action breaks down the pathogen into fragments (Ag)
Endoplasmic reticulum produces MHC II proteins
Ag fragments will bound to MHC ll proteins and will be presented on the cell membrane
MHC II and Antigen complex on the surface of membrane will activate T cells

45. Antigens and MHC Proteins

46. B cells and Antibody Mediated Response
B cells produce specific Ab
There are millions of B-cells - each with specific Ab on its membrane
When B- cells are activated they can produce up to 100 million Ab per hour

47. Antibodies structure Antibodies are Y-shaped proteins consisting of:
Two parallel polypeptide chains
Heavy chains and light chains
Constant region and variable region
Antigen binding site

48. Antibody Structure

49. Antibody Structure

50. Actions of antibodies include:
Neutralization
Agglutination and precipitation
Activation of complement
Attraction of phagocytes
Opsinization
Stimulation of inflammation
Prevention of adhesion

51. Classes of Antibodies (immunoglobins)
IgG – resistance against many viruses, bacteria and bacterial toxins
IgE – accelerates local inflammation and responsible for allergic reaction
IgD – found on the surface of B cells
IgM – first type secreted after antigen arrives
IgA – primarily found in glandular sec

52. Primary and secondary antibody response
Primary response
Takes about two weeks to develop
Produced by plasma cells
Secondary response
Rapid increase in IgG
Maximum antibody titer app

53. Aging and the Immune Response
Immune system becomes less effective
Increased susceptibility to infection
Immune surveillance declines
With age

54. You should now be familiar with:
The structure and function of lymphatic cells, tissues and organs
The body’s nonspecific defenses and the components and mechanisms of each
Specific resistance, cell-mediated immunity and antibody mediated immunity
The role of the T cell, B cell and antibodies in specific immunity
The origin, development, activation and regulation of normal resistance to disease
The effects of stress and aging on the immune system