The document discusses the adaptive immune response, highlighting its two main components: humoral immunity mediated by B lymphocytes and cellular immunity mediated by T lymphocytes. It explains the maturation of these cells in primary lymphoid organs, their action in secondary lymphoid organs, and the mechanisms involved in the antibody response and T cell activation. Additionally, it distinguishes between active and passive immunity, detailing their characteristics, effectiveness, and duration.

1. Adaptive(Acquired)
Immune Response
By
Prof. S.B Zailani
Chief Consultant Clinical Microbiologist

2. Strategy of Adaptive
Immune Response
 First response to particular antigen called
primary response
 May take a week or more to develop
 Immune system remembers pathogen on
subsequent exposure
 Termed secondary response
 Adaptive immunity divided into
 Humoral immunity
 Eliminates extracellular pathogens
 Cellular immunity
 Eliminates intracellular pathogens

3. Strategy of Adaptive
Immune Response
 Overview of humoral immunity
 Mediated by B lymphocytes
 B cells
 Develops in bone marrow
 B cells may be triggered to proliferate into plasma
cells
 Plasma cells produce antibodies
 Antibodies produce when antigen binds B cell receptor
 Some B cells produce memory cells

4. Strategy of Adaptive
Immune Response

5. Strategy of Adaptive
Immune Response
 Overview of cellular immunity
 Mediated by T lymphocytes
 T cells
 Matures in thymus
 Divided into 2 subsets
 Cytotoxic T cells
 Helper T cells
 T cell receptors help with antigen recognition

7. Anatomy of the Lymphoid System
 Lymphoid system collection of tissues and
organs designed to bring B and T cells in
contact with antigens
 In order for body to mount appropriate response,
immune cells must encounter antigen
 Lymphoid system includes
 Lymphatic vessels
 Secondary lymphoid organs
 Primary lymphoid organs

8. Anatomy of the Lymphoid System

9. Anatomy of the Lymphoid System
 Lymphatic vessels
 Carry lymph to body tissues
 Lymph formed as result of body’s circulatory system
 Lymph travels through vessels to lymph
nodes
 Material such as protein is removed
 Fluid portion empties back into blood stream

10. Anatomy of the Lymphoid System
 Primary lymphoid organs
 Bone marrow and thymus are primary lymphoid
organs
 Location where stem cells destined to become B and T
cells mature.
 B cells mature in bone marrow
 T cells mature in thymus
 Once mature, cells leave primary lymphoid organs and
migrate to secondary lymphoid organs

11. Anatomy of the Lymphoid System
 Secondary lymphoid organs
 Sites where lymphocytes gather to encounter
antigens; organs include
 Lymph nodes
 Spleen
 Tonsils
 Adenoids
 Appendix
 Organs situated strategically
 Allows for initiation of immune response from nearly
any place in body

12. Clonal Selection
of Lymphocytes
 Lymphocyte characteristics include:
› Immature
 Antigen specific receptors not fully developed
› Naive
 Have antigen receptor but have not encountered antigen
› Activated
 Able to proliferate
 Have bound antigen
› Effectors
 Descendents of activated lymphocytes
 Able to produce specific cytokines
 Plasma cells, T helper and cytotoxic T cells effector cells
› Memory lymphocytes
 Long-lived descendents of activated lymphocytes
 Memory cells responsible for seed and effectiveness of
secondary response
 Remembers antigen on subsequent exposure

13. B Lymphocyte and
Antibody Response
 Antigen binds to B cell receptor
 Poises B cell to respond
 In many cases B cell needs confirmation from helper T cells
 Ag enters the body and is phagocytozed and processed by
macrophages
 These macrophages destroy Ag and present a portion on the
surface of the macrophage next to self Ag
 Macrophages are called antigen-presenting cells (APC)
 Processed Ag combines with specific TH with the appropriate
receptor
 APC releases substances to activate TH cell
 TH cell activates B cells to divide and differentiate
› Produce plasma cells and memory B cells

14. B Lymphocyte and
Antibody Response

15. B Lymphocyte and Antibody Response
 Characteristic of primary response
 Lag period of 10 to 12 days occurs before antibody
detection in blood
 Activated B cells proliferate and differentiate into increasing
numbers of plasma cells as long as antigen is present
 Net result is slow steady increase in antibody titer

16. B Lymphocyte and
Antibody Response
 Class switching
 B cells initially programmed to differentiate into plasma cells
 Plasma cells secrete IgM antibodies
 Helper T cells produce cytokines
 Some B cells switch programming
 Differentiate to plasma cells that secrete other classes of
antibodies
 Commonly IgG

17. B Lymphocyte and
Antibody Response
 Formation of memory
 B cells that have undergone class switching
 Produce IgG antibody
 IgG is antibody of memory
 IgG antibody can circulate in body for years allowing
protection against specific antigens

18. B Lymphocyte and
Antibody Response
 Characteristics of secondary response
 Memory cells responsible for swift effective
reaction of secondary response
 Often eliminate invaders before noticeable harm is
done
 Vaccine exploits phenomenon of immunologic
memory
 Some memory B cells will differentiate into
plasma cells
 Results in rapid production of antibodies

19. T Lymphocytes
Antigen Recognition and Response
 General characteristics of T cells
 Have multiple copies of T cell
receptors
 Receptors have variable sites of
antigen binding
 Role of T cells different from B cells
 T cells never produce antibodies
 T cells armed with effectors that
interact directly with antigen
 T cell receptor does not react with
free antigen
 Antigen must be presented by
APC

20. T Lymphocytes
Antigen Recognition and Response
 General Characteristics
 During antigen presentation, antigen cradled in
grove of major histocompatability complex
molecule (MHC molecule)
 Two types MHC
 MHC class I
 Bind endogenous antigen
 MHC class II
 Bind exogenous antigen

21. T Lymphocytes
Antigen Recognition and Response
 General characteristics
 Two major function T cell populations
 Cytotoxic T cells
 Proliferate and differentiate to destroy infected or
cancerous “self” cells
 Have CD8 marker
 Recognize MHC class I
 Helper T cells
 Multiply and develop into cells that activate B cells and
macrophages
 Stimulate other T cells; orchestrate immune response
 Have CD4 marker
 Recognize antigen display by MHC class II

22. T Lymphocytes
Antigen Recognition and Response
 Functions of Tc (CD8) cells
 Induce apoptosis in “self” cells
 Cells infected with virus or intracellular
microbe
 Destroys cancerous “self” cells
 Nucleated cells degrade portion of
proteins
 Load peptides into groove of MHC class I
molecule
 MHC class I molecule recognized by
circulating Tc cell
 Cell destroyed by lethal effector function of Tc
cell
 Tc cells releases pre-formed cytokines to
destroy cell

23. T Lymphocytes
Antigen Recognition and Response
 Functions of TH (CD4) cells
 Orchestrate immune response
 Recognize antigen presented by MHC class II molecules
 MHC class II molecules found only on APC
 If TH cell recognizes antigen, cytokines are delivered
 Cytokines activate APC to destroy antigen

24. T Lymphocytes
Antigen Recognition and Response
 Role of TH cells in B cell activation
 If TH cell encounters B cell bearing peptide: MHC
class II complex
 TH cell responds by producing cytokines
 B cell is activated in response to cytokine
stimulation
 B cell proliferates and undergoes class switching
 Also drives formation of B memory cells

25. T Lymphocytes
Antigen Recognition and Response
 Role of TH cells in macrophage
activation
 Macrophages routinely engulf
invading microbes resistant to
lysosomal killing
 TH cells recognize macrophage with
engulfed microbes resistant to
killing
 TH cells activate macrophages by
delivering cytokines that induce
more potent destructive
mechanisms

26. Natural Killer Cells
 Natural killer cells descend from lymphoid
stem cells
› They lack antigen specificity
 No antigen receptors
 Recognize antigens by means of Fc portion of IgG
antibodies
 Allow NK cells to attach to antibody-coated cells
 Actions augment adaptive immune response
› Important in process of antibody dependent
cellular toxicity
 Enable killing of host cells with foreign protein in
membrane
 Natural killer cells recognize destroyed host
cells with no MHC class I surface molecules
› Important in viral infection

27. Lymphocyte Development
 During lymphocyte development, B and T cells
acquire ability to recognize distinct epitopes
 Once committed to specific antigen, cells “checked
out” to ensure proper function
 B cells undergo developmental stages in bone
marrow
 T cells go through process in thymus

28. Active immunity Passive immunity
 1, Need active participation
of self immune system.
 2, Acquisition:-
i, natural disease process
ii, vaccination(killed or live)
iii, toxoid
 3.Effectiveness:- High
 4. Time required to
develop: 5 to 14 days
 1. It does not
 2.
i)Passing of IgG
vertically
ii)Injection of
readymade antibodies
 3. low
 4. Immediately

29. Active immunity Passive immunity
 5.Duration of
effectiveness:-
Longer (months-
years)
 6.Reactivation:-
By giving booster
dose
 7.Use:-
prophylaxis
 5. Days to weeks
 6. No reactivation
 7.Prophylaxis and
Therapy

30. Summary of Adaptive Immune Response

31. Thank You for Listening