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