AID, Hypermutation and B-Cell Lymphoma
AID is the only enzyme in the body whose job is to damage DNA on purpose. It deaminates cytosine at the immunoglobulin locus, and the lesions that follow produce somatic hypermutation in the variable region and class-switch recombination at the constant region \u2014 one enzyme, two outcomes, distinguished only by where the damage lands. Selection then keeps whichever cell came out binding better. The targeting is good but not exclusive, and the off-target lesions are where MYC ends up beside an immunoglobulin enhancer in Burkitt lymphoma and BCL2 does the same in follicular lymphoma. BCL6 is what makes the whole thing survivable, by repressing the DNA-damage response \u2014 which is another way of saying the reaction runs with its safety system switched off. This map follows the mutagenesis: what licenses it, what performs it, what restrains it, and what the cells that survive it turn into. Click any protein for the matching Assay Genie In Vivo antibody or ELISA kit.
One enzyme, two outcomes, and the difference is only where the lesion lands. AID deaminates cytosine to uracil in single-stranded DNA at the immunoglobulin locus. Repair of that lesion in the variable region, by error-prone polymerases, produces somatic hypermutation; repair of clustered lesions in the switch regions produces the double-strand breaks that drive class-switch recombination. Nothing distinguishes the two activities at the enzyme \u2014 the distinction is made by where transcription exposes single-stranded DNA. That is why AID cannot be engineered to do one and not the other, and why its off-target activity is not a separable defect but a property of the same mechanism.
BCL6 switches off the safety system, which is what makes the reaction possible. A cell cannot deliberately mutate its own genome while a functioning DNA-damage checkpoint is watching, so BCL6 represses that response \u2014 including p53 target genes \u2014 for the duration. The consequence is that germinal-centre B cells tolerate breaks that would arrest or kill any other cell, and that BCL6 translocations, which lock that state on, are among the commonest lesions in diffuse large B-cell lymphoma. The transcription factor that defines the reaction and the one that transforms it are the same protein.
The lymphomas are where the off-target lesions ended up. The MYC translocation of Burkitt lymphoma and the BCL2 translocation of follicular lymphoma both juxtapose an oncogene to an immunoglobulin enhancer, which is exactly what AID-initiated breaks at two loci, mis-joined, would produce. The output band of this map is not incidental to it: CD20, CD38, CD52, CD79b and BCMA are the antigens that rituximab, daratumumab, alemtuzumab, polatuzumab and belantamab are aimed at \u2014 the therapeutic targets of the malignancies this reaction generates. One expression detail carries most of the clinical weight: CD20 is absent from plasma cells, which is why B-cell depletion spares the antibody-secreting compartment and why serum antibody persists after rituximab.
The In Vivo tie-in, and where the map is thin. 23 of the 36 nodes carry a functional-grade antibody, and they are all upstream of the mutagenesis. The help that licenses AID is blockable end to end: CD40 in both species (mouse FGK4.5 ultra-low endotoxin, human G28-5), ICOS, CD28, CD80, CD86 and CTLA-4 (clone 9D9). That matters more here than on a conventional germinal-centre map, because how much help a B cell receives sets how long it stays in the reaction and therefore how much mutation it accumulates \u2014 titrating help is the only practical way to control mutational load in vivo. Around them sit B220 (RA3-6B2), CD19, class II in both HLA-DR and HLA-DQ, PD-1 (RMP1-14) with PD-L1 (10F.9G2), CD70, CD3 (145-2C11), CD4 (GK1.5), CD8 (Ly-2), CXCR3, SIGN-R1, IL-10, TGF-\u03b2, human CD20 and an in vivo-grade anti-BCMA. Stated plainly, the mutagenesis itself cannot be touched: AID is research grade, BCL6 and CD40L are ELISA only, and CXCR5 and IL-21 \u2014 the marker and the cytokine that define the helper cell \u2014 are ELISA only as well. The lymphoma targets the reaction produces are biosimilar: CD79b, CD38, CD52, BCMA, along with BAFF, BAFF-R, CD27 and IL-6R. The workable design is therefore to titrate the help and read the mutational output, rather than to interrupt AID. One reagent caution: the CD40 agonist is stocked ultra-low endotoxin, and that is not a formality \u2014 LPS activates B cells directly and would be scored as CD40 agonism. For research use only; not for use in diagnostic or therapeutic procedures.
Every protein node links to a product — ELISA kit, In Vivo antibody or research antibody.