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.
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)
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
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
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
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
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
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
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
