Immunology what are TdT and AID and what are their roles in

Solution

Answer-TdT stands for terminal deoxynucleotidel transferase.i t is a special kind of DNA polymerase expressed immature pre B and pre T lymphocytes.Unlike other DNA polymerase TdT has a unusual function to synthesize DNA without using template DNA.

AID-AID stands for activation induced cytidine deaminase.i T is a 24kDa enzyme in human which is responsible for antibody diversity.d ye to its deamination activity it deaminase it causes mutation in DNA by deamination of cytosine to uracil and thus change base pairs G-C to U-Aor T-A due to these mutation in germinal center of B lymphocytes antibody diversity produces.

Role of TdT and AID in B cells-Bcells are immune cell that produces antibody with the binding sites for antigen. Different types of antibodies produced by B cell which give immunity to different type of antigens.These antibody diversity occure due to VDJ recombination .In antibody producing pre B cells rearrangement of these variable(v), diversity (D), joining (J)gene segments allow B cells to generate antibody with different antigen binding sites with antibody specificity.For breaking,arranging and rejoining these gene segments district classes of enzymes like nuclease ,ligase and polymerase work.S specific kind of polymerase used for these gene recombination known as TdT.

RAG enzyme cut- the double standard DNA which contains genes .and the hairpin structure left is open by Artemis complex which has endonuclease activity.once Artemis complex open hairpin and add palindromic sequence in DNA cut end TdT start working on 3\'OH end of DNA and add nucleotide to single stranded DNA in 5\'to3\' direction without using template.single stranded DNA formed at both the ends of non homologous segment joining done by Watson and Crick base pairing and unpaired bases are removed by exonuclease ,gap is filled by template dependent polymerase and Nick is sealed by ligase.in this way due to the recombination of antibody diversity producing gene pre B cells produces diffrent type of antibody specific to different type of antigen.

AID produces mutation in B cells during germinal center development by deamination of cytosine that produces antibody diversity.

CD-R are the part of variable chain in immunoglobulin generated by B cells and T cell receptor.tdt and AID helps to crate these sites on antibody and create antibody diversity.