Advanced Course in Immunology On Demand Lecture Recordings-The Generation and Modification of Lymphocyte Antigen Receptor Genes

Video Transcription

Video Summary

The transcript is a lecture on how B and T cells generate antibody and receptor diversity for adaptive immunity, and how these processes are tightly regulated to avoid genome damage and cancer.<br /><br />It first explains V(D)J recombination, the developmental process in the bone marrow and thymus that assembles antigen receptor genes from separated V, D, and J segments. The lecture reviews the classic Tonegawa discovery that immunoglobulin genes are rearranged in lymphocytes, not fixed in germline DNA. Recombination is directed by recombination signal sequences (RSSs) and the 12/23 rule, and is carried out by the RAG1 and RAG2 proteins. RAG cuts the DNA, forming signal ends and hairpin coding ends, which are then repaired by the non-homologous end joining (NHEJ) pathway. Junctional diversity is created by imprecise end processing, nucleotide addition by TdT, and trimming, greatly increasing receptor diversity. The speaker also describes chromatin accessibility, enhancer control, loop extrusion, and allelic exclusion as mechanisms that regulate when and where recombination occurs.<br /><br />The second half covers B-cell-specific diversification after antigen exposure: class switch recombination and somatic hypermutation. Class switching changes antibody constant regions without altering antigen specificity, allowing different effector functions such as IgM, IgG, IgA, and IgE. This process depends on AID, transcription through switch regions, R-loops, and repair pathways that generate double-strand breaks and recombine switch sequences. Somatic hypermutation introduces point mutations into variable regions in germinal centers, where B cells compete for higher affinity antigen binding, leading to affinity maturation.<br /><br />The lecture ends by emphasizing the oncogenic risk of these DNA break and repair processes and how checkpoints like ATM and p53 help protect lymphocytes.

Asset Subtitle

Lecture 6: Eugene M. Oltz, The Ohio State University, Wexner School of Medicine

Asset Caption

The Generation and Modification of Lymphocyte Antigen Receptor Genes

Keywords

V(D)J recombination

adaptive immunity

B cells

T cells

RAG1 RAG2

RSS 12/23 rule

NHEJ repair

junctional diversity

class switch recombination

somatic hypermutation

AID enzyme

affinity maturation