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ADAPTIVE IMMUNITY
Adaptive immunity
• Specific
• Slow during the primary response, but
very fast during the secondary responses
• memory
Specificity is achieved by BCRs and TCRs
Each B cell express a unique BCR and each T cell
express a unique TCR
Clonal selection!
B cell receptor (BCR)
HUMORAL RESPONSE
Circulating B cells which have not
been exposed to the antigen 
naive B cells
When BCR binds to the antigen, the
antigen is internalised by the B cell
and presented to the T cells
• Activated t cells induce
- Cell surface proteins (CD40L)
- Cytokines
- Activated B cell divide rapidly and differntiate to
plasma cell
- This events take in germinal centres of
lymphnodes and spleen
• The first IG is always IgM
• Later different cytokines instruct B cells to
secrete different IG classes (isotype
switching)
IG diversity
• Differnt gene segments on different
chromosomes encode heavy and light
chains
• These multigene families are separated by
non-coding regions and are brought
together with gene rearrengements.
Light chain
• V  about 76
• J5
• C1
Heavy chains
V 123-129
D  27
J9
C 11
Recombinase
activating gene
RAG-1 and RAG
2 recombinase
responsible for the
VDJ recombination
• Isotype switching:
• IL-4  IgG and IgE
• IL-5  IgA
• DNA sequences known as “switch sites” are located
upstream of heavy constant region on the DNA (M, D, G,
E and A)
• IgM and IgD do not have switch sites
• Affinity maturatin  Somatic hypermutation (random
mutationx in V regions)
Cell mediated immunity
• CMI is the major
component of immune
response
• T cell are essential cells
influencing
• Cytokine production, B
cell activation,
macrophage activation,
rejection, killling of tumor
or infected cells, DTH
TCR
• Gamma-delta
TCR bearing cells
are found in
skin, epitelial and
intestinal layers
• Antigen
recognition is
MHC restricted
• Alfa-gamma V,
D and J;
• Beta, delta  V
and J
rearrengements
• No somotic
hypermutation
•
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•
TH17
CD4+ cells producing IL-17 and 22
Early immune response to bacteria
Autoimmunity
Immunity against fungi
• Treg
• CD4+CD25 +
• FOXP3