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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 cellsWhen 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 chainsV 123-129D 27J 9C 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
• TH17• CD4+ cells producing IL-17 and 22• Early immune response to bacteria• Autoimmunity• Immunity against fungi
• Treg
• CD4+CD25 +• FOXP3