Download - Chapter 15:Adaptive Immune Response
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
IgMProduced 1st
Complement activationPrimary function =
neutralize pathogens in the bloodstream
10 antigen binding sites
5 classes of antibodies
IgGLongest half-lifeSmall enough to
cross endothelium bbb, some types of placenta
Main antibody produced in 2° immune reactions
5 classes of antibodiesIgAMonomeric & dimeric
Dimer = secretory IgAsIgA = most abundant AbSecreted across mucosal surfaces
in mucus & many other secretions (tears, saliva, milk)
Binding → neutralize toxins, block viral and bacterial attachment
5 classes of antibodies
IgEBound to Fc region of
mast cells and basophils
Cross-linking of IgE by antigen → degranulation
5 classes of antibodies
IgDActivation of
basophils & mast cells
Activation of B cellsHighly conservedFunctions 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
•Affinity maturation• Class switching IgM → IgG IgM → IgA
Memory B cells+ memory helper T cells: long lived (years)
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