Chapter 15:Adaptive Immune
Response
General Characteristics
• Involves specialized WBC’s known as
lymphocytes
• Response is highly specific, evolves
throughout an organisms life-time
• Response generates memory
• Can discriminate between HEALTHY self and
non-self OR between HEALTHY self and
DAMAGED self
The Adaptive Immune Response
• Primary response
• Secondary response
• Humoral immunity:
– B cells, plasma cells, antibodies: target
extracellular pathogens
• Cell-mediated immunity
– T cells, dendritic cells – antigen is inside a cell
Overview of the Adaptive Immune Response
Anatomy of the Lymphoid System
• Lymphatic Vessels
• Secondary lymphoid Organs
• Primary Lymphoid Organs
Lymphocytes are responsible for the specific
immune response
What promotes an immune response?
• Antigens
– Usually proteins or polysaccharides
– Foreign substance with MW of 10,000 daltons
– Examples of microbial antigens: bacterial capsules,
cell walls, flagella, toxins of bacteria
Antibodies bind antigens
Some molecules are not recognized as antigens until
bound to another
How are antigens recognized?
•
•
•
•
Self markers also known as MHC markers
MHC (major histocompatibility complex)
MHC Class I-produced by all body cells
MHC Class II-produced by B cells, T cells, and
antigen presenting cells
Structure of an antibody
5 classes of antibodies
IgM
Produced 1st
Complement
activation
Primary function =
neutralize
pathogens in the
bloodstream
10 antigen binding
sites
5 classes of antibodies
IgG
Longest half-life
Small enough to
cross endothelium
bbb, some types of
placenta
Main antibody
produced in 2°
immune reactions
5 classes of antibodies
IgA
Monomeric & dimeric
Dimer = secretory IgA
sIgA = most abundant Ab
Secreted across mucosal
surfaces in mucus & many
other secretions (tears,
saliva, milk)
Binding → neutralize toxins,
block viral and bacterial
attachment
5 classes of antibodies
IgE
Bound to Fc region of
mast cells and
basophils
Cross-linking of IgE by
antigen →
degranulation
5 classes of antibodies
IgD
Activation of
basophils & mast
cells
Activation of B cells
Highly conserved
Functions minimally
elucidated
What can happen when
antibody binds antigen?
How are B cells activated?
B cell activation by Helper T cell
Primary and secondary response to antigen
Memory B cells+
memory helper T cells:
long lived (years)
•Affinity maturation
• Class switching
IgM → IgG
IgM → IgA
Helper T cells help activate other immune
cells
T cells
• Have own T cell receptor (TCR)
• Do not make antibodies
• Must recognize MHC markers which
“present” antigen
MHC markers
Cytotoxic T cells recognize MHC Class I
markers
Helper T cells recognize MHC Class II
Dendritic cells can activate T cells
Cytotoxic T cells
Cytotoxic T cells
Cytotoxic T cells identify infected body cells
Helper T cells activate
macrophages
Helper T cells activate B cells
T cell-independent antigens
Antibody-dependent cell-mediated
cytotoxicity