1. Immune system and Immunity
A short course

2. Immunity
Definition ;
It is a homeostatic condition in which the body maintains protection against infection and tumor growth.
It is a series of delicately balanced complex, multi-cellular and physiological mechanisms that allow an individual to distinguish foreign material from ‘self ’ and to neutralize and /or eliminate the foreign matter ‘non-self ’.

3. Structure of the immune system

5. Lymph node

6. Distribution of the lymph nodes

7. The spleen

8. The thymus gland

14. Phagocytosis
Macrophages
APC
Bifunctional
Antigen
presentation
Liver
Skin
Spleen,lung
CNS
Kuppfer cells
Denteritic cells
Microglia
Macrophages

15. Functions of the immune system
*Types of immunity
-Natural or innate immunity
-Acquired or adaptive immunity

16. Innate immunity First response Non-specific Natural components
Soluble factors
Immune cells (phagocytes)
Barriers
Secretions
Membranes
Complement
Acute phase protein

17. Acute phase proteins Upon infection Macrophages (Kuppffer cells)
activated
Bind to bacteria to
Facilitate complement
fixation
Secrete different
cytokines
Go systemically
Still high through the
The course of infection
fever
Acute phase response
Serum amyloid A&B +
C-reactive protein

18. 2) Complement Facilitate phagocytosis It is a group of serum proteins
(about 30) can bind to bacteria
Coating of bacteria
(Opsonization)
Complement receptors can
interact with phagocytes
Facilitate phagocytosis

19. Antigen presentation
Antigen presenting cells (APC) are those can introduce the antigens to the T-cells. APC are
B-cells , macrophages and denteritic cells. Foreign antigens are handled by APC cells through phagocytosis and where they are fragmented .
Then, they are interacted with MHC-class II to form a
complex that is able to be recognized by the T-helper cells.

20. Foreign antigen CD4+ Macrophage Interact with T-helper cells
Early endosome
Processing
compartment
Peptide binds class-II
MHC-class II
Transport vesicle
Macrophage

21. Immune response T-cell activation Th1 CD4+ CD8+ Th2 Cytokines
APC + T-cell interaction
Activate APC
(macrophages)
TNFά
Auto-activation
IL2
Recognize MHC-class II
In extracellular antigen
e.g bacteria
Th1
CD4+
CD8+
Th2
Activate macrophages
Activate B-cells
Antigen elimination
Recognize MHC-class I
In intracellular antigen
e.g virus, cancer cells
Produce antibodies
Plasma cells

22. Thymic education Thymus CD8+ CD4+ CD8+ CD4+ CD8+ B-cell
Negative selection
Thymus
Pre-T-cell
CD4+
CD8+
CD8-CD4-
CD8-
CD4+
CD4-
CD8+
Begin TCR gene
rearrangement
Positive selection
Stem cell in
bone marrow
Lymphoid cell
In the bone
Marrow equivalent
to what in the thymus
Begin Ig gene
rearrangement
CD4+
CD8+
B-cell
Can recognize
MHC-class-I
Plasma cells
(Ab)
Can recognize
MHC-class-II

24. Assessment of the integrity of the immune system
General assessments:
Blood analysis
Histopathology of the thymus and the spleen or
other lymph nodes
Relative organ weigh e.g relative spleen,thymus weights
Bone marrow function
Lymphocytes subsets
PFC plaque forming cell assay
Apoptosis in immune cells
Lymphocyte proliferation assay
Host-resistant assay
HDR (Delayed hypersensitivity assay

25. Lymphocyte subset assay by flowcytometric analysis
Rationale : specific antibodies are performed against different
cellular receptors then added to the target cells . These antibodies
(primary) will characterize the target cell then interact with
secondary ones that is conjugated with FITC the allowed to pass
Through very small orifice as one cell at the time. This cell pass
through laser beam and undergo florescence then their number is
detected by specific detector.

26. Lymphocyte proliferation assay;
Rationale: Lymphocytes are stimulated for proliferation by
specific lectins LPS for b-cells , Con-A and PHA are specific
for T-cells. Cells grow in culture media in presence of
Tritiated thymidine then it will be incorporated in the de novo
DNA synthesis and it is equivalent to the cell proliferation.
Host-resistant assay
Rationale: killer agent such as bacteria , virus, or cancer cells
Are injected to experimental animals e.g mice the the death
rate is recorded .Then another group of animals are exposed to the
agent or condition that needed to be examined on the immune
System then injected with the same dose of the killer agent and the
death rate recalculated.

27. PFC assay;
Rationale:
A group of mice challenged with SRBCs then sacrificed and the
spleens are collected after few days. Then they are incubated in
presence of complement and SRBCs in vitro. The challenged
Splenocytes will contain the cells that are able to form the
antibodies against SRBCs and destroy it to form plaques that
could be counted under light microscope. Another group
of animals are exposed the agent under test and then
repeat the previous experiment. Number of plaques will
reflect the effect on the humoral immunity as will
as the ability of the T-cell, macrophages and B-cells
to integrate to form the proper immune response.