Adaptive Immunity Undergraduate MBBS Class

1. ADAPTIVE IMMUNITY
Sayantan Banerjee

2. Immune System
There are two major line of defences:
•Innate Immunity
•Adaptive Immunity

5. INNATE IMMUNITY ADAPTIVE IMMUNITY

8. Adaptive Immunity: characters
• The Adaptive immune system, also known as the
• Acquired immunity or, more rarely, as the
• Specific immune system
• Can specifically recognize pathogens: Therefore needs
Receptors or recognition interfaces
• Major Antigenic receptors: The ANTIBODIES

10. Role of the Antibodies
A)RECEPTOR / RECOGNITION function:
Sticking to the offender pathogen / molecule
A)EFFECTOR / BIOLOGICAL function:
A)Complement Activation
B)Phagocytosis of the pathogen by activating
phagocytes

13. Role of the Antibodies (repeated)
A)RECEPTOR / RECOGNITION function:
Sticking to the offender pathogen / molecule
A)EFFECTOR / BIOLOGICAL function:
A)Complement Activation
B)Phagocytosis of the pathogen by activating
phagocytes

15. Role of the Complement activation
A) MAC (membrane attack complex) mediated killing
of the pathogens
B)Opsonization & enhanced phagocytosis
C)Chemotaxis of phagocytes
D)Increased vascular permeability and Inflammation

16. CLONAL SELECTION

17. C
L
O
N
A
L
P
R
O
L
I
F
E
R
A
T
I
O
N

20. Cell mediated Immunity: for intracellular
pathogens
• Some organisms (intracellular bacteria and viruses) survive
within the Macrophages by subverting the innate killing
mechanism of the cell
• They are thus secluded from the Humoral adaptive Immune
system
i.e. out of reach of the antibodies
• The Macrophages can’t kill them but can process small
antigenic fragments (of dead organisms) and place them on
the host (Macrophage) cell surface.

21. Humoral
&
Cell
mediated
Immunity

22. MHC molecules
• Discovered in 1940’s during studies of rejected transplant
tissues hence known as “histocompatibility complexes”
• Multiple blood transfusion recipients and Organ transplant
recipients were found to have circulating Antibodies
against donor
• Multiparous women were found to have circulating
Antibodies against husband
• These antibodies were found to bind to the Leukocytes of
the donor / husband, hence known as “Leukocyte antigens”

23. Class I MHC molecules
• Class I MHC: Constitutively expressed on ALL NUCLEATED cells
• Each cell display SIX (6) different MHC- class I molecules
encoded by two different alleles (paternal and maternal) of HLA-
A, HLA-B and HLA-C genes.
• Behaves as a Framework for expression of endogenous (cytosolic
or nuclear) antigens
• They express:
• Self antigens
• Tumour antigens
• Viral antigens
• They are recognized by CD8+ Cytotoxic T-cells and NK cells.

24. Class II MHC molecules
• Class II MHC: Constitutively expressed on Antigen
Presenting cells (Dendritic cells, Macrophages, B-
Lymphocytes)
• Behaves as a Framework for expression of exogenous
(phagocytosed) antigens
• They express:
• Phagocytosed extracellular pathogens’ antigens
• Viral antigens
• They are recognized by CD4+ Helper T-cells.

26. T-helper cells CD4+
• Recognizes only antigens presented by Antigen presenting
cells: i.e.
• Dendritic cells
• Macrophages
• B-Lymphocytes (Remember: special function)
• Recognizes only phagocytosed exogenous antigens bound
to MHC Class II
• Function: secrete cytokines that causes:
• B-Lymphocytes to produce Antibodies
• Macrophage activation to kill its intracellular
organism (by IFN-γ)

27. CD4+ T Helper cells

28. Cytotoxic-T cells CD8+
• Recognizes antigens presented by All cells.
• Recognizes all endogenous antigens bound to MHC Class I
• Function: secrete cytokines that causes:
Killing of the cells harbouring WRONG molecules.

29. Killing of virus
infected cells:
specific CD8+
Cytotoxic T cells
&
nonspecific NK
cells

30. CD8+ Cytotoxic T-Lymphocyte killing

31. a

32. a

37. MHC: Sausage on a barbecue Model

38. T Cell
receptor

39. T Cell
Receptor

40. • The activation of
lymphocytes requires
two distinct signals, the
first being antigen and
the second being
molecules that are
produced during innate
immune responses to
microbes or injured
cells.
• This idea is called
the two-signal
hypothesis for
lymphocyte activation.

43. CD4+ T Cells: differentiation
•Th 1 cells :
•Can secrete various cytokines but signature
Cytokine is IFN-γ
•Other cytokines: TNF, Lymphotaxin, IL-2
•Activate Macrophages & Dendritic cells,
enhancing their ability to kill intracellular
organisms
•Very important in killing intracellular Bacteria,
Viruses and Protozoa (e.g. Salmonella, Tb,
Leishmania)

44. CD4+ T Cells: differentiation
• Th 2 cells :
• Can secrete various cytokines but signature Cytokines
are IL-4, IL-5, IL-13
• Other cytokines: IL-9, 10, 25
• Activate B-Lymphocyte differentiation & Antibody
production, Eosinophil recuritment & Mucous
production, enhancing their ability to kill intracellular
organisms
• Important in killing Helminths of Gut
• Involved in Allergic diseases
• Actually reduces immune response to intracellular
pathogens