Microbiology with diseases by body system;

1. Overview of
Adaptive Immunity
Microbiology and immunology_2
The third line of defense

2. Overview of Adaptive Immunity
 Adaptive immunity is the body’s ability to recognize and defend
itself against specific pathogens and their products
 Adaptive immunity
 Specificity (acts against specific pathogens)
 Induced (activated in response to specific pathogens)
 Clonality (induced cells proliferate to form clones)
 Self-tolerant (it does not act against self antigens)
 Memory (faster and more effective response to a subsequent
infection caused by the same pathogen)

3. Adaptive immunity involves the activity of lymphocytes
 Two main types of lymphocytes
 B cells
 T cells
Adaptive Immunity
A resting lymphocyte
 B cells form and mature in
the red bone marrow
 T cells form in the red
bone marrow and mature
in the thymus
 Both B and T cells are found in the blood and lymphoid organs

4.  Adaptive immunity involves two types of responses
 Humoral immune responses (humoral immunity)
 Activated B cells produce antibodies that function against
extracellular pathogens in the blood
 Cell-mediated immune responses (cellular immunity)
 Activated T cells function against infected host cells
(intracellular pathogens)
 Regulate adaptive immune responses
Adaptive Immunity

5. Components of adaptive immunity
Lymphatic system
Allows for immune system surveillance
 Lymphatic vessels conduct lymph from tissues and return it to the
circulatory system
 Lymph: fluid leaked from blood vessels into surrounding
tissues
 The lymphatic system includes lymphoid tissues and organs
 Red bone marrow and thymus
 Lymph nodes
 Tonsils, spleen
 Mucosa-associated lymphatic tissue-MALT

6. Lymphatic
system
 Lymph nodes
are the site of
activation of B cells
and T cells
 Contain
phagocytic cells
(macrophages and
dendritic cells)

7. Epitopes or antigenic determinants
 Antigens are molecules the
body recognizes as foreign
 Their binding to defensive
cells can trigger adaptive
immune responses
 Antigens are recognized by
the shape of regions called
epitopes
 Microbial antigens include:
Components of the cell walls, capsule, flagella or toxins, proteins and
glycoproteins of viruses, fungi, or protozoa

8. Exogenous and endogenous
antigens

9. Clonal deletion
 The body eliminates
lymphocytes that react
against self-antigens
 Lymphocytes that react to
self-antigens undergo
apoptosis
 Leading to the development
of self-tolerance
It is vital that immune responses are not directed
against self-antigens

10. Humoral response involves activation of B cells
 The precise binding of
the receptor on the B
cell to the epitope
 Determines the
specificity of a humoral
immune response
 All the BCRs on a single B cell are the same

11.  The binding of the epitope to the BCRs stimulates the B cells to
undergo cell division
 Cell division gives rise to activated B cells called plasma cells
Humoral response involves activation of B cells
 Plasma cells secrete
antibodies or
immunoglobulin (Ig) in the
blood and lymph
 Immunoglobulins have
identical antigen-binding
sites as the BCRs of the
activated B cells

12.  Y-shaped molecules
with two antigen-
binding sites
 Five classes of
immunoglobulins
 IgG
 IgA
 IgM
 IgE
 IgD
Immunoglobulins

13. T cells
Cytotoxic T (Tc) cells Kill viral (or other pathogens)
infected host cells
Helper T (Th) cells Help regulate the activities of B
cells and cytotoxic T cells
Regulatory (suppressor) T cells Help prevent autoimmune disease
Cell-mediated immune responses involve T cells
 Immunosystem cytokines act as intercellular signals among all
cell types of the immune system

14.  Viruses and other intracellular pathogens
 Receptors of T cells are
called TCRs
 TCRs do not recognize
epitopes directly
 TCRs bind epitopes
associated with proteins
called MHC (Major
Histocompatibility
Complex)
T cells allow the body to fight against intracellular
pathogens

15. MHC - Major Histocompatibility Complex
 MHC proteins hold
and position antigenic
determinants for
presentation to the T
cells
 First identified in graft
patients - determine
compatibility of tissues
for tissue grafting
 Found in the membrane of most cells of vertebrate animals

16.  APCs
 B cells
 Macrophages
 Dendritic cells
APCs (Antigen presenting cells) and MHC
Dendritic cells typically found in
skin and mucous membranes
 APCs migrate to lymph
nodes where they
present the antigen to
the T cells
 Antigen is bound to
MHC on the surface of
the APCs

17.  Initiate adaptive immune responses in lymphoid organs –
lymph nodes - where the APCs interact with lymphocytes
 The initial event is the activation of cytotoxic T cells
 Effector cytotoxic T cells will leave the lymph node ready
to attack virally infected cells
The body does not initiate adaptive immune responses at the
site of an infection
Cell-mediated immune responses

18. Cell-mediated
immune responses
 Interaction
between APC cells, T
helper cells, inactive
cytotoxic T cells,
cytokines
 Leads to activation
of cytotoxic T cells
 Formation of
Memory T cells
Details of the figure will not be part of your
next exam!!!

19. Cell-mediated immune responses
 Effector cytotoxic T cells will
attack virally infected cells
 Recognize viral epitope on MHC I
of infected cells and
 Induce apoptosis of infected cells
 Memory T cells persist in
lymphoid tissues
 Exposure to the same antigen
will trigger an effective
response called a memory
response

20. Humoral Immune Responses
 Humoral antibodies are effective against pathogens that
are circulating freely so that the antibody can contact them
 Two types of humoral response
 T-independent humoral immunity
 T-dependent humoral immunity
Humoral immune responses are mounted against exogenous
pathogens

21. T-independent humoral immune responses
 Occurs without involvement
of helper T cells
 T-independent responses are
reduced in children
 Pathogens with T-
independent antigens can
cause disease in children that
are rare in adults
 Haemophilus influenzae type b (capsule) causes meningitis in
unvaccinated children

22. Most humoral responses
are of the T-dependent
type
 Interaction between
APC cells, helper T
cells, B cells
 Leads to activation of B
cells plasma cells
will produce antibodies
 Formation of Memory B
cells
 Lymph nodes/cytokines
mediate interactions Details of the figure will not be part of your
next exam!!!

23. Functions of immunoglobulins
 The binding of antibodies to antigens to form antibody-antigen
complex tags the pathogen/toxins for destruction
 Several mechanisms are involved
 Agglutination by IgG and IgM

24.  Opsonization
 Neutralization
Functions of immunoglobulins
 Activation of complement
system (classical pathway)

25. Functions of
immunoglobulins

27.  Produced by B cell proliferation
 BCRs complementary to antigenic determinant that
triggered their production
 Long-lived cells that persist in the lymphoid tissue
 Initiate antibody secretion if antigen is encountered again
Memory B cells and the establishment of immunological
memory

28. Immunological Memory
 Primary response occurs after initial contact with an antigen
 Secondary (memory) response occurs after second exposure
 Antibody titer is
the relative amount
of antibodies in
serum

29. Administration of a tetanus
toxoid in immunization
Subsequent exposure to active
tetanus toxin
Immunological Memory

30. Colostrum
IgG/IgA