This document summarizes the development and functions of T and B lymphocytes. It discusses how they develop from stem cells in the bone marrow or thymus, and how T cells undergo selection processes in the thymus. It describes the roles of cytotoxic T cells, helper T cells, and B cells, and how B cells differentiate and produce antibodies. The document also provides a brief overview of HIV/AIDS, including the virus structure and life cycle.

1. T and B lymphocytes

2. Content of the lecture
1. Birth of T & B Lymphocytes.
2. How they grow up?
3. What purpose they are serving in your body?
4. Little bit about MHC.
5. AIDS
6. Kaun Banega Crorepati !!

3. Birth of T & B Lymphocytes
a. In fetus, blood cell
precursor is found in liver
and yolk sac.
b. In adult, blood cell
precursor is found bone
marrow.
Stem Cell
Erythroid
Myeloid
B lymphocytes
Lymphoid
T lymphocytes

4. T lymphocytes selection in thymus
Pre
thymocytes
Thymus
Thymic
epithelial
cells
TCR
Death
Death
Death

5. T lymphocytes selection in thymus
CD 4+
CD 8+
TCR
CD 4+
CD 8TCR
Differentiation of double positive
cells into a single positive cell (either
CD 4+ or CD8+) upon contact with
either class II or class I MHC
protein.
CD 4CD 8+
TCR

6. What is the function of T lymphocyte?
Cytotoxic T cell
• Extracellular pathogen
Antibodies
• What if the pathogen is predominantly intracellular?
• T cells continuously scan all the cell surfaces and kill
those that exhibit foreign antigen.
• “Cut & display” method used by all the cells of the body.
The peptide of the intracellular intruder is displayed in
association with MHC I protein.
• Scanning cytotoxic cells (CD8+) then destroy the
infected cell.

7. What is the function of T lymphocyte?
Helper T cell
• Helper T cell (CD4+) recognizes peptides bound to MHC class II and
not class I.
• They scan APCs like macrophages, dendritic cells and B cells.
• The peptide attach to MHC II comes from proteins that are
internalized by endocytosis.
• Helper T cells then signals the B cells to proliferate and produce Ig.
• Presentation of peptide attached to MHC I is a call for destruction.
• Presentation of peptide attached to MHC II is a call for help.

8. B lymphocytes
Stem Cells
Antigen
Independent phase
Pre B Cells
µ
Immature B cells
Antigen Dependent
phase
Activated B cells
Plasma cells

9. B lymphocytes

10. Functions of Immunoglobulin
1.

11. Functions of Immunoglobulin
2.

12. Functions of Immunoglobulin
3.
Toxin receptors
Bacterial toxins
Host
cell
Neutralization by antibody
Forming phagosome Fc
receptor
Phagocytosis of
antibody-antigen
complex by
macrophage

13. Functions of Immunoglobulin
4.
Bacteria in plasma
Lysis and
ingestion
C1
C2
C4
C1 C2C4
Complement
activation
Digestion in lysosome

14. Class Switching

15. Class Switching
An antibody-producing cell first synthesizes IgM and then makes either IgG, IgA,
IgD, or IgE of the same specificity. In this switch, the light chain is unchanged.
Furthermore, the variable region of the heavy chain stays the same. Only the constant
region of the heavy chain changes. This step in the differentiation of an antibodyproducing cell is called class switching.

16. HIV & AIDS
1. Virus Coat
2. Viral Core
3. Enzymes
4. Nuclear Material
5. Genes

17. HIV Life Cycle
1. Entry
2. Reverse Transcription and Integration
3. Transcription and Translation
4. Assembly, Budding and Maturation

19. Question Round (True/False)
1. Macrophages have receptors for Fab fragment of Immunoglobulin molecule on their
surfaces.
2. Antibody specificity is determined by the amino acid sequence of the variable regions of
both light and heavy chain.
3. IgA acts as a first line of defense against bacterial and viral antigen.
4. A child stung by a bee experiences respiratory distress within minutes and lapses into
unconsciousness. This reaction is probably mediated by IgM.
5. AIDS is caused by a human retrovirus that kills CD8+ cells.
6. After binding to its specific antigen, a B lymphocyte may switch its constant region of the
immunoglobulin light chain.

20. Spot the immunoglobulin?
IgM

21. Maximum concentration of this immunoglobulin is
present in which of the following?
Secretory Piece
A. Urine
B. Heart
C. Clostrum
D. All of the above
J Chain/
T Piece

22. This is an example of ………………?
A. Isotypic Difference
B. Allotypic difference
C. Idiotypic difference

24. Thank you very much!