1. Immunology
Dr Shoaib Raza

2. Immune System Defense system
Fights against bacterial and other infections
Rejects the foreign tissue or organ
Necessary for life
Can cause disease
Too low immunity - Immune deficiency
Too high immunity - Autoimmune disorders

3. Types of Immunity Innate Immunity Acquired Immunity Since birth
Nonspecific
Exposure independent
Similar response
Means
Skin
Mucus membranes
Gastric acid secretion
Tears (Lysozyme)
Inflammation
Acquired Immunity
Acquired during life
Specific
Exposure dependant
Variable magnitude
Means
T- Cells
B- Cells

4. Types of Immunity Active Immunity: Passive Immunity: Can be induced by
Infection or subclinical infections
Antigen administration (Immunization)
Passive Immunity:
Can be :
Transferred from mother to fetus
Induced by administration of antibodies

5. Active versus Passive Immunity
Active Immunity
Active involvement of immune system
Infections, subclinical infection
Vaccination
Delayed onset
Longer lasting
Memory cells formation
Passive Immunity
Passive involvement of immune system
Passive transfer of antibodies
Preformed antibodies
Readily available
Transient
No memory cell formation

6. Types of Immunity Cell Mediated Immunity Humoral Immunity
Mediated by T-Cells (CD4+ or CD8+ T Lymphocytes)
Humoral Immunity
Mediated by antibodies formed from plasma cells
Plasma cells are formed after activation of B- Cells

7. Immune System Organs Cells Primary lymphoid organs
Bone marrow
Secondary lymphoid organs
Lymph node, tonsils, spleen etc
Tertiary lymphoid organs
Formed in follicular inflammation
Cells
Lymphocytes
Macrophages
Polymorph cells
Other cells like platelets, endothelial cells etc

8. Lymphocyte 30-45% of all WBC Roughly 2100 cells/mm3 of blood
T- Cells (60%)
B- Cells (30%)
NK Cells (10%)

9. T- Cells Formed in primitive yolk sac in embryo Migrate to bone marrow
Preprocessed and differentiates into Thymus
Recognized cell bound antigens
Present in the paracortical areas of lymph node
Two types:
CD4+ T cells – Regulatory cells (2/3rd of all T cells)
CD8+ T Cells – Effector cells (1/3rd of all T Cells)

10. Lymph Node Histology

11. Thymic Education
Preprocessing, processing, differentiation and clonal expansion of T Cells occurs in thymus
T Cells enter from primitive yolk sac into thymus
TCR + lymphocytes
Develop two proteins, CD4 and CD8
Double positive T Cells

12. Thymic Education
In the thymic cortex they come in contact with either MHC I or MHC II
Lose one of the protein, i.e. either CD4 or CD8 (Single positive T Cells)
Those who do not bind with either MHC I or MHC II are negatively selected for apoptosis
Those who bind firmly are selected positively for apoptosis

13. Thymic Education
Thus either CD4+ or CD8+ T cells (single + T Cells) leave thymus and enter peripheral circulation.
T-Cells thus educated have following characteristics:
Can only recognized antigen presented to them in association with either MHC I or MHC II
Do not recognize self proteins as antigens (Tolerance)

14. T-Cell Activation T-Cell activates through two signals
Antigen binds to TCR
MHC II or I binds to either CD4 or CD8
Co-stimulatory signal binds to CD3 group of proteins
Clonal expansion (proliferation)
Memory cell formation

15. T-Cell Activation

16. Types of CD4+ T-Cells Th-1 cells: Th-2 cells:
Secretes IL-1, IL-2, γ-IFN etc and activates other T Cells (CD8+, CD4+ and induce cell mediated immunity), macrophages etc
Th-2 cells:
Secretes IL-4 or IL-5, (BCGF & BCDF) and activated B Cells to proliferate and synthesize antibodies (inducing humoral immunity)

17. B Cells Are present in lymphoid follicles
Can recognize circulating antigen (do not require antigen presentation)
Gets differentiated into plasma cell in the germinal centre of lymphoid follicle
IL-4 and IL-5 from T Cells help in growth and differentiation of B Cells
Secretes antibodies

18. Antibodies These are gamma globulins Secreted by plasma cells
Also called as immunoglobulin
Five classes
Immunoglobulin G
Immunoglobulin M
Immunoglobulin A
Immunoglobulin D
Immunoglobulin E

19. Plasma Cell

20. To be continued……