1. IMMUNITY .

2. Outline Anatomy of the Immune system
Organization of the body’s defenses
Humoral immunity
Cell-mediated immunity
Immune responses in Health and diseases

3. The Immune system
Immunity refers to protection against infections, and the immune system is the collection of cells and molecules that are responsible for defending against the pathogenic microbes in environment

4. The Immune system Role: protect body against pathogens
Pathogens; bacteria, bacterial toxin, viruses, parasites, and fungi.

5. Outline Anatomy of the Immune system
Organization of the body’s defenses
Humoral immunity
Cell-mediated immunity
Immune responses in Health and diseases

6. Anatomy
Leukocytes
- Phagocytes (phagocytosis): neutrophils, eosinophils, monocytes, macrophages, dendritic cells (skin)
- Lymphocytes: Bs and Ts, natural killer cells
- Mast cells
Lymphoid tissues
- primary lymphoid tissues (bone marrow and thymus)
- secondary lymphoid tissues

7. Outline Anatomy of the Immune system
Organization of the body’s defenses
Humoral immunity
Cell-mediated immunity
Immune responses in Health and diseases

8. Organization of the body’s defenses
Non-specific defenses: no need to decipher pathogen’s identity. Always present in the body.
- Physical barriers
- Inflammation
- Interferons
- Natural cell killers (NK cells)
- Complement system
Specific defenses:Based on recognition of the pathogen’s identity
Humoral immunity
Cell-mediated immunity

9. Non-specific defenses
Physical barriers
- skin
- mucus
- stream of tears or urine
- Inflammation
Chemical barriers
pH (stomach, vagina)
enzymes (stomach, tears)
Interferons
Complement system .

10. Inflammation
Symptoms of inflammation:
Redness
heat
Swelling
- pain

11. Macrophage and phagocytosis

12. Interferon Protein secreted by a cell currently infected by a virus
Interferon warns the neighboring cells of the impending viral infection
The neighboring cells synthesize proteins that will block the virus from hijacking the cell DNA replication machinery

13. Complement system About 30 blood proteins
They become activated either by direct contact with a pathogen or by contact with a bound antibody.
In an activated state, they form a complex which opens a hole in a pathogen’s cell membrane  bacterial lysis
Complement system also promotes inflammation

14. Natural Killer cells = NK cells
Cytotoxic T cells, lacking markers
Able to recognize a wide range of pathogens without prior exposure
When recognition and binding occur, the NK cells destroy the pathogen through cell lysis .

15. Specific immunity
Specificity: based on shape recognition of cell surface antigens
Diversity: Any shape can be recognized by a B or T-lymphocytes and trigger an immune reaction
Memory: once a pathogen has activated the immune system, memory cells remain and will protect against a secondary infection
Self-tolerance: the immune system does not attack itself

16. Players of Specific immunity
Macrophages (antigen presenting cell = APC): phagocytize pathogens and present antigens to helper-T lymphocytes
Helper-T lymphocytes: secrete lymphokines and activate B and killer T lymphocytes
B-lymphocytes: multiply and specialize into plasma cells  secrete antibodies
Killer-T lymphocytes: kill (through lysis) infected or cancerous cells

17. Antibody-mediated (humoral) immunity = AMI
Macrophages phagocytize a pathogen and present an antigen to a matching helper-T cell
At the same time, some pathogens contact B-cells matching the pathogen’s antigens
The helper-T cells multiply, secrete lymphokines which stimulate the B-cells to multiply and specialize into plasma cells
The plasma cells secretes antibodies

18. .

19. What are antibodies? . Structures formed by 4 proteins
Two main regions:
the upper region is highly variable and bind to a specific shape (the antigen)
The base region is constant for all antibodies this region, when the antibody is bound to its antigen, activates the complement system .

20. Role of the antibodies

21. Types of antibodies Antibody = immunoglobulin = Ig
IgG Most abundant. mostly in blood, lymph. able to cross the placenta
IgA  Found in tears, milk, blood, lymph
IgM  Found in blood, lymph. unable to
cross placenta
IgE  Found on mast cells, basophiles. involved in allergic reaction.
IgD  Found in blood, lymph, on B cells

22. First and second exposures to a pathogen

23. Clonal selection
Once a T, B or killer lymphocytes have made contact with their specific antigen, they are triggered into action but they also divide and form a large amount of identical cells, called a clone.

24. Clonal deletion
How can the DNA in the nucleus codes for each type of antibody?
Since over a millions of different types are needed, how can the DNA in the nucleus code for each of them? There is clearly not enough DNA to accomplish that.
During embryogenesis, several genes coding for the variable portion of the antibody (and each responsible for part of a shape) reshuffle so each combination of genes codes for a specific antibody (and shape). So a stem cell receives the capability to form one single type of antibody.
Once formed, they circulate in the body. If they meet and bind to a shape (formed by a protein) present in the body, they are destroyed or deleted, so that only the stem cells responsible for antibodies aimed at foreign pathogens are left.
A stem cell able to react with our own proteins and not deleted during fetal life might later trigger an autoimmune disease. .

25. Cell-mediated immunity
Similar reaction to AMI
The pathogen triggering the reaction is a virus infected cell or a cancerous cell.
Killer T lymphocytes are sensitized by contact and activated by lymphokines secreted by activated helper T lymphocytes

26. CMI .
Figure (1 of 2)

28. Cell Mediated: MHC MHC occurs as two classes
MHC I on virtually all tissue cells
MHC II only on APC’s and Lymphocytes.

29. Cell Mediated: MHC display properties
MHC I on virtually all tissue cells
Display only proteins produced inside the cell
Endogenous antigens = foreign proteins produced by the cell (viral / cancer)
Stimulate the CD8+ cell population
form cytotoxic T-cells (Killer T, TC)

30. .

31. Cell Mediated: MHC display properties
MHC II found only on T-cells & APCs
Display proteins derived from a phagocytized target
Exogenous antigen: foreign protein from outside the cell – presented to surface
Stimulates the CD4+ cell population
form Helper T-cells (TH)

32. .

33. Clinical applications
Immunization
- Active and natural
- Active and artificial
- Passive and natural
- Passive and artificial