1. Defenses mechanisms (Immunity)
The human body has the ability to resist almost all types of organisms or toxins that tend to damage the tissues. This capacity is called immunity.
Body defense against potential pathogens can be grouped in 2 categories:
- Innate immunity.
- Adaptive immunity.

2. quick to develop highly targeted, INNATE IMMUNITY antigen non-specific
ADAPTIVE IMMUNITY
Antigen specific
highly targeted,
exhibit memory.

3. Innate immunity a- External defenses:-
Inherited, and represent first line of defense.
a- External defenses:-
* Skin: acts as a physical barrier to penetration by pathogens.
* Digestive tract: includes the high acidity of stomach and protection by normal bacteria in colon.
* Respiratory tract: include secretion of mucus,
movement of mucus by cilia, alveolar macrophages.
* Genitourinary tract: include acidity of urine and
vaginal lactic acid.

4. b- Internal defense:- I- Phagocytic cells II- Natural killer cell
III- Interferons
IV- Endogenous pyrogens

5. I- Phagocytic cells:
There are 3 major groups of phagocytic cells:-
- Neutrophils
- Monocytes in blood and macrophages (derived from monocytes) in the connective tissues.
- Organ specific phagocytes in the liver (kupffer cells), spleen, lymph nodes, lung and brain (microglia).

6. II- Natural Killer cell
lymphokines
kills transformed and malignant cells
kills malignant cells
IFN
IFN
IL2
IL2

7. III- Interferons They inhibit replication of viruses.
- Alpha and beta interferons can be produced from all cells of the body,
- Gamma interferon is produced only by particular lymphocytes and natural killer cells.
Alpha interferon is now being used to treat hepatitis C.

8. IV- Endogenous pyrogen
(as interleukin-1, interleukin-6 and tumor necrosis factor)
secreted by leukocytes and other cells  produces fever, increased sleepiness and a fall in plasma iron concentration  inhibit bacterial activity.

9. Adaptive (acquired) immunity
It is the ability of human body to develop antibodies and sensitized lymphocytes
against individual invading agents such as bacteria, viruses, and toxins.
specific
highly targeted,
exhibit memory

10. It is of two types
1-Humoral immunity:
by circulating antibodies
2-Cell-mediated immunity:
by activated lymphocytes

11. Development of the immune system:
During fetal development, lymphocytes precursors come from the bone marrow and mature in 2 sites
(1)Thymus gland
In this gland, Thymopoietin transfere
the lymphocytes precursors into T-lymphocytes  responsible for cellular immunity

12. (2) Fetal liver and spleen
In which the lymphocytes precursors are transformed into B-lymphocytes
The B-lymphocytes differentiate into
plasma cells (Humoral immunity)
and memory B-cells
After development the 2 types (T & B) migrate to the lymph nodes and bone marrow

13. Bone marrow lymphocytes precursors
T-lymphocytes
Bone marrow lymphocytes precursors
Cellular immunity
Humoral immunity
B-lymphocytes
(liver-spleen)
(Thymus)
Memory T-cells
Cytotoxic
T-cell (T8)
Helper
T-cell (T4)
Supressor
T-cell
Stimulation
(+)
Inhibition
(-)
Plasma cells
Memory B-cells
Stim. (+)
Inh. (-)

14. Activation of a clone of lymphocytes
When bacterial or other foreign antigens first enter the body ingested by the macrophages  exposure part of the ingested antigen (antigen presentation) on their surfaces .
Then these macrophages contact the lymphocytes  activation of helper-T4 cells  secrete lymphokines  proliferation and transformation of B-lymphocytes into plasma cells and memory B-cells or activation of clone of T-lymphocytes and memory T-cells

15. Humoral immunity
The plasma cells secrete large amount of specific antibodies (immunoglobulins)
Plasma cells produce about 2000 antibody protein/sec.

16. Immunoglobulins: Structure:
Their basic components are 4 polypeptide chains 2 long (heavy) and 2 short (light) joined by disulfide bridges
It has 3 sites
- Antigen-binding sites (the variable portion)
- Complement binding (the constant portion)
- Macrophage binding sites

19. Types of immunoglobulins
(1) IgG
Highest blood concentration (73%).
Low M.W
It can cross capillary walls and placenta to reach the fetal circulation and give the fetus passive immunity during early life
Responsible for formation anti-Rh
antibodies.

20. (2) IgM It can not cross capillary or the placenta
- 7% of serum antibodies
High M.W (macroglobulin) =
It is made of 5 immuno-globulins units linked by disulphide bonds to provide 10 combining sites
It can not cross capillary or the placenta
It is responsible for ABO system antibodies

21. (3) IgA - 19% of serum antibodies - Low M.W 170.000
- It is present in the mucous membrane and secretion of the body as respiratory tract secretion, nasal secretion, saliva, tears, intestinal secretion and clostrum of the breasts producing localised protection

22. (4) IgE (5) IgD -Very low serum level -M.W 190.000
- It is responsible for immediate hypersensitive reactions as in bronchial asthma, hay fever and urticaria. It also increased in parasitic infestations.
(5) IgD
- Trace amount & its function are unknown

23. Functions of T lymphocytes in cellular immunity
T lymphocytes provide specific immune protection without secreting antibodies.
This is provided by the 4 populations of T lymphocytes:-
1- The killer (cytotoxic) cells
2- The helper T lymphocytes
3- The Suppressor T lymphocytes
4- Memory T cell

24. 1- Cytotoxic T8 lymphocytes
They must be in physical contact with victim cells. Then they secrete perforins and lysosomal enzymes that enter victim cells and destruct them.
Killer T cells defend against viral and fungal infections and are responsible for transplant rejection reactions.

25. 2- Helper-T4 cells (75%)
- They increase the activation of T & B cells by interleukin II secretion
- They activate macrophage system
-The causative virus of AIDS, destroy these cells causing cell immune deficiency

26. 3- Suppressor T8 cells
- They suppress the function of B and other T cells so called regulatory T cells
- The helper T cells activate the suppressor T cells, which in turn suppress the helper (negative feed-back).
- They play a role in limiting the immune system to prevent the autoimmunity

27. 4- Memory T cells
They are responsible for the second response of the same antigen, which occur more rapidly and powerful than the first response

28. Secondary immune response
The memory T & B cells
persist in the body for years and
readily converted to effector cells
by exposure to the same antigen
 more rapid and greater immune response
as in vaccination.

29. Tissue transplantation
T-lymphocytes of the recipient develops immune response to these tissue grafts and rejection occurred.
So the patient uses some drugs to depress the cytotoxic T-cells and inhibit helper T-cells e.g., Glucocorticoids
Autoimmune disease
The body may produce an immune response against it’s own proteins

30. Acquired immunodeficiency syndrome (AIDs)
Human immunodeficiency virus (HIV-retro virus)
attacks the helper (T4) lymphocytes blocking its effect on proliferation of T8 cytotoxic and B-cells
 loss of immune function
 death from mild infections