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Adaptive Immunity
1. Vertebrates only
2. Specificity
- recognition modules - BCR, Ab and TCR
- gene rearrangement is the source of diversity
- clonal selection
3. Small lymphocytes
- types and sub-types
- functions
Recognition concept
Receptor or Antibody molecule
Antigen - structure recognized by an Ab, BCR or TCR
Epitope - particular sub-structure of the Ag that is bound
Affinity - how much a molecule likes to bind to a structure
Small lymphocyte sub-types
B-cells
BCR is Immunoglobulin (Ig)
Plasma cells - effector cells that secrete Ab
T-cells
Tc = cytotoxic (CD8+)
TH = helper T-cells (CD4+)
Th1 (inflammation)
Th2 (help B-cells make AB)
Recognition modules of Adaptive immunity
B-cell receptor
B cells
T cells
Native vs
Denatured
B-cells
T-cell
Antigen
processing
Major
Histocomp
-atibility
(MHC)
How does MHC work?
APC - Antigen
Presenting Cells
Professional
APC
- macrophages
- B cells
- Dendritic cells
Intracellular
pathogens
Extracellular
pathogens
All nucleated cells
APC
Only immune cells
Professional APC
Figure 1-26
MHC class I communicates with Tc cells
MHC class II communicates with TH cells
Figure 1-27
Dendritic cells interact with naïve T-cells and initiate differentiation
How do Antibodies work?
Parasitic infection
Parasite
+
Mast cell
Inflammation
Mast cell
activated
Expel
and/or
destroy
pathogen
•
•
•
Neutralization
Opsonization
Inflammation
Principles of Adaptive Immunity
Diversity
Specificity
Memory
Self-tolerance
Gene Rearrangement is the source of Diversity
Germline configuration
Diversity
1. Alternative combinations
2. Imprecise joints
3. Different types of chains
4. B-cells - somatic hypermutation
In the absence of antigen
Clonal Selection
1. Each cell = one receptor
2. Millions of lymphocytes
are generated
3. Small subset will
recognize a pathogen
4. Proliferation and
differentiation
5. Acquired immunity - the
adaptive immunity
provided by
immunological memory
Antibodies are usually very specific
Figure 1-22
Concept Behind Vaccination
Figure 1-30
Some memory
lymphocytes
Few specific
Many
lymphocytes
lymphocytes
•Pre-industrialization infants built
immunity naturally
•Post-industrialization polio rate
increased in adults hence a need for
vaccination
Polio Vaccine - Inactive vs Oral “live” version
VDPV - vaccine derived polio virus
- mutations can lead to polio at extremely low rate
Principle of Self-tolerance
B-cells with BCR that bind to self will undergo Apoptosis
More complicated scheme of selection for T cells
Selection of T cells
1. Thymocytes
2. Positive selection
-Self MHC
3. Negative selection
Mechanism of Self-tolerance
Immunodeficiencies
Inherited deficiencies
e.g. Bubble boy disease
Stress induced
nutrition, emotional
Pathogen caused deficiencies
HIV - attacks CD4 T lymphocyte
Cells and molecules
involved in
Hypersensitivity Diseases
Figure 1-32
• IgE
• IgG
• CD4 TH1
• CD8 CTL
Insulin-Dependent Diabetes Mellitus
Figure 1-33
Beta cells of the Islets of Langerhans
Inflammatory Adaptive Immune Response
Figure 1-34
Hygiene Hypothesis