The document summarizes key aspects of cellular and humoral immunity. It describes how antigens are processed and presented by antigen-presenting cells, which then activate T cells. There are three main classes of T cells: cytotoxic T cells that directly attack foreign cells, helper T cells that promote other immune responses, and memory T cells that provide future immunity. The document also outlines antibody-mediated humoral immunity, where B cells produce antibodies against antigens to help remove them from the body.

1. Hafiz Waqar Ahmed Baber
560-FBAS/BSBT/S14
Department of Biotechnology
Faculty of Basic and applied sciences

2. Cell mediated and
Antibody mediated
immunity

3. Antigens
 Antigens have 2
characteristics
 Immunogenicity: Ability to
provoke immune response
 Reactivity:Ability of antigen to
react specifically with antibodies it
provoked
 Entire microbes may act as antigen
 Typically, just certain small parts of
large antigen molecule triggers
response (epitope or antigenic
determinant)

4. Antigen Processing

5. Cellular Immunity
 T cells attack foreign cells and diseased host cells; memory of Ag
 Three classes of T cells
1. Cytotoxic T cells (Tc cells) carry out attack
2. Helper T cells: help promote Tc cell and B cell action and nonspecific
defense mechanisms
3. Memory T cells: provide immunity from future exposure to antigen

6. MHC Proteins
Membrane glycoproteins, bind to antigens,
encoded by chromosome 6, form MHC.
2 Classes of MHC Proteins
Class I: found in membranes of all nucleated
cells
Pick up small peptides in cell and carry them to
the surface:
T cells ignore normal peptides
abnormal peptides or viral proteins activate T cells
to destroy cell
Class II: found in membranes of antigen-
presenting cells (APCs)
found in lymphocytes Antigenic fragments

7. Antigens and MHC Proteins
Figure 22–16a (Navigator)

8. Antigen-Presenting Cells (APCs)
 Responsible for activating T cells against foreign cells and proteins
Phagocytic APCs :
 Free and fixed macrophages:
 in connective tissues
 Kupffer cells:
 of the liver
 Microglia:
 in the CNS

9. Pinocytic APCs
 Langerhans cells:
 in the skin
 Dendritic cells:
 in lymph nodes and spleen

10. Figure 22–16b
Antigen Presentation

11. Mechanism of T cell recognition
and activation

12. Antigen Recognition
 Inactive T cell receptors:
 recognize Class I or Class II MHC proteins
 recognize a specific antigen
 Binding occurs when MHC protein matches antigen

13. TC cell Recognition
 Antigen presentation
 MHC-I proteins
 found on nearly all nucleated body cells
 display peptides produced by host cells
 TC cell activation
1. binding of cytotoxic T cells (CD8 cells) to abnormal
peptides on MHC-I and
2. costimulation via a cytokine
 triggers clonal selection: clone of identical T cells
against cells with same epitope

14. TH cell Recognition
 Antigen presentation
role of MHC-II proteins
found only on antigen
presenting cells
display only foreign antigens
stimulate helper T cells (CD4
cells)

15. CD Markers
 Also called cluster of differentiation markers:
 in T cell membranes
 molecular mechanism of antigen recognition
 more than 70 types:
 designated by an identifying number
CD3 Receptor Complex
 Found in all T cells

16. CD8 Markers
 Found on cytotoxic T cells and suppressor T cells
 Respond to antigens on Class I MHC proteins
CD4 Markers
 Found on helper T cells
 Respond to antigens on Class II MHC proteins
 CD8 or CD4 Markers - Bind to CD3 receptor complex
 Prepare cell for activation

17. Costimulation
 For T cell to be activated, it must be costimulated:
 by binding to stimulating cell at second site
 which confirms the first signal

18. 2 Classes of CD8 T Cells
 Activated by exposure to antigens on MHC proteins:
 one responds quickly:
 producing cytotoxic T cells and memory T cells
 the other responds slowly:
 producing suppressor T cells

19. TH cell Activation
1. binding of helper T cells
(CD4 cells) to epitope
displayed on MHC-II of APC
2. costimulation via a
cytokine
3. triggers clonal selection

20. TH cell Activation

21. Activation of Helper T Cells
Figure 22–18
Helper T Cells -
Activated CD4 T
cells divide into:
active helper T
cells:
secrete
cytokines
memory T cells:
remain in
reserve

22. Attack Phase: Role of Helper
T Cells Secretes interleukins
attract neutrophils,
NK cells,
macrophages
stimulate
phagocytosis
stimulate T and B cell
mitosis and
maturation
Coordinate humoral
and cellular
immunity

23. Figure 22–17 (Navigator)
Activation of Cytotoxic T
Cells
Also called
killer T cells
Seek out
and
immediatel
y destroy
target cells

24. Actions of Cytotoxic T Cells
1. Release perforin:
 to destroy antigenic cell membrane
2. Secrete poisonous lymphotoxin:
 to destroy target cell
3. Activate genes in target cell:
 that cause cell to die

25. Slow Response
 Can take up to 2 days from time of first exposure to an
antigen, for cytotoxic T cells to reach effective levels

26. Memory Tc Cells
 Produced with cytotoxic T cells
 Stay in circulation
 Immediately form cytotoxic T cells:
 if same antigen appears again

27. Suppressor T Cells
 Secrete suppression factors
 Inhibit responses of T and B cells
 After initial immune response
 Limit immune reaction to single stimulus

28. 4 Functions of Cytokines
1. Stimulate T cell divisions:
 produce memory T cells
 accelerate cytotoxic T cell maturation
2. Attract and stimulate macrophages
3. Attract and stimulate NK cells
4. Promote activation of B cells

29. Figure 22–19
Pathways of T Cell Activation

30. Humoral Immunity
 Recognition
 B cell receptors bind antigen, take in and digest antigen then display epitopes
on its MHC-II protein
 After costimulation by TH cell, divide repeatedly, differentiate into plasma cells,
produce antibodies specific to that antigen
 Attack
 antibodies bind to antigen, render it harmless, ‘tag it’ for destruction
 Memory
 some B cells differentiate into memory cells

31. Humoral Immunity - Recognition
21-
31

32. B Cells
 Responsible for antibody-mediated immunity
 Attack antigens by producing specific antibodies
 Millions of populations, each with different antibody molecules
Sensitization
 Corresponding antigens in interstitial fluids bind to B cell receptors
 B cell prepares for activation
 Preparation process is sensitization

33. Figure 22–20 (Navigator)
B Cell Sensitization
and Activation
During sensitization, antigens are taken into
the B cell, processed, reappear on
surface, bound to Class II MHC protein

34. Helper T Cells
 Sensitized B cell is prepared for activation, but needs helper T cell
activated by same antigen
B Cell Activation
 Helper T cell binds to MHC complex:
secretes cytokines that promote B
cell activation and division

35. B Cell Division
 Activated B cell divides into:
 plasma cells -Synthesize and secrete antibodies into
interstitial fluid
Memory B cells-Like memory T cells remain in
reserve to respond to next infection

36. Any Question

37. Thank you