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Immunology final

Terms in this set (48)

After being infected/activated, Naive B cells have the potential to switch to any isotype via Class Switch Recombination (CSR) and Somatic Hypermutation (SMH). SMH, which occurs in the germinal center (GC), produces individual point mutations in the Ig heavy and light chains but the heavy chain is what determines the isotype. The CSR is driven by an enzyme complex, then 2 cuts are made: 1st one is always before the Cμ(M) and C𝞭(D). The second cut however depends on the cytokines produced by Tf cells in the GC, and this cut can either occur right before the CƔ(G), or Cε(E), or Cɑ(A). Tf cell expresses the CD40 ligand producing 3 cytokines IFNƔ, IL-4, and TGFβ : If there's a lot of IFNƔ, IgG will be produced, IL-4 for IgE, and TGFβ for IgA. IFNƔ also activates STAT1 which activates AI promoter for CƔ2a induction of transcription in the I region promoter opens up the DNA, which allows an enzyme Activation Induced Cytidine Deaminase (AID). AID accesses the switch regions and converts single stranded RNA to Uracil. Two other enzymes, UNG and APE1, convert into single stranded nicks in the DNA on both of the strands. These activities create multiple breaks in the DNA μ switch region, and because these breaks happen in different regions far apart from each other, the double strand break machinery joins the two and excises out all the DNA in between. The remnants of the 2 damaged regions, which has now become the new constant region, is only a few kilobases of the VDJ region. The new transcription is now of the new isotype, IgE, which becomes expressed on the B cell surface.