BIOL233 Immune Systems Unit 6 Quiz

Lymphocyte Development and Production

• Lymphocytes are white blood cells divided into B lymphocytes and T lymphocytes.
• Formation occurs from pluripotent stem cells in the bone marrow, guided by lymphoid progenitor cells.
• Lymphocyte identity as B or T cells is determined by anatomical site (bone marrow for B cells, thymus for T cells) and gene expression changes during differentiation.

B and T Lymphocyte Development Stages

• B lymphocyte development occurs entirely in the bone marrow, while T lymphocyte development involves migration to the thymus.
• Three types of T cells exist: CD4 T cells and CD8 T cells (both expressing the α/β TCR) and γ/δ T cells (expressing the γ/δ TCR).

Lymphocyte Receptor Genes

• B cells generate immunoglobulins (Igs), and T cells produce T cell receptors (TCRs) to recognize diverse antigens.
• Each receptor must exhibit unique antigen specificities, aggregating a vast repertoire.

Gene Segment Composition

• Igs consist of 2 heavy chains and 2 light chains, while TCRs comprise an α-chain and β-chain.
• Approximately 300 different gene segments code for the receptors, allowing for the production of 10^9 to 10^14 unique surface receptors.

V(D)J Recombination

• This genetic mechanism enables lymphocytes to rearrange gene segments, enhancing receptor diversity.
• Each precursor cell undergoes rearrangement resulting in specific immunoglobulin or TCR gene assembly.

B-Lymphocyte Receptor Genes Structure

• Igs contain variable (V) and constant (C) regions, encoded by three loci: heavy locus (chromosome 14), kappa locus (chromosome 2), and lambda locus (chromosome 22).
• K-light chain is structured with a single constant region and a variable region formed by numerous gene segments, enabling diverse antigen binding.

K-Light Chain Rearrangement

• DNA segments fold and join via excision, leading to rearrangement and formation of the primary mRNA transcript, ultimately translated into a protein.

Antigen Binding Specificity

• Igs possess three Complementarity Determining Regions (CDRs) critical for binding specific antigens, particularly CDR3 influenced by V and J segments.
• λ-light chains, while structurally similar to k-light chains, have different numbers of functional genes and segments.

Heavy Chain Gene Rearrangement

• Variable regions of heavy chains are encoded by segments similar in organization to the k-light chain, including additional D segments.
• Two rearrangements occur: joining one D segment to one J segment, then one V segment to one D segment, influencing antibody class.

T-Lymphocyte Receptor Genes Overview

• TCR genes, encoding for α and β chains, exhibit a cloning structure akin to Ig genes, enabling similar V(D)J rearrangements.
• TCR α gene includes one C region and numerous V and J gene segments, whereas TCR β gene consists of V, D, and J segments, with corresponding constant region genes.

Diversity of Antigen Specificity

• The extensive genetic diversity in both B and T lymphocyte receptor genes ensures the immune system can recognize and respond to an ordinary spectrum of pathogens.