B Cell and T Cell Diversity Quiz

B Cell and T Cell Diversity Generation

• Each individual produces over 1 million unique B cell antigen receptors and 10 million unique T cell antigen receptors.
• Human genome contains approximately 20,000 protein-coding genes, raising questions about the generation of receptor diversity.
• Immune system creates a vast array of antigen receptors by combining different genetic elements, similar to selecting from multiple options (e.g., sizes and colors of a cell phone).

Immunoglobulin (Ig) Gene Structure

• Immunoglobulin genes encode essential components for B cell antigen receptors and secreted antibodies (immunoglobulins).
• Ig light chain is formed from three gene segments: variable (V), joining (J), and constant (C).
• The V and J segments determine the variable region of the receptor, while the C segment specifies the constant region.

Specifics of Light-Chain Gene

• The light-chain gene consists of:
  • One constant (C) segment
  • 40 different variable (V) segments
  • 5 different joining (J) segments
• This structural organization enables a diverse combination of V and J segments, contributing to the variability of antigen receptors in B and T cells.

Mechanism of Diversity

• The diversity in antigen receptors results from the random selection and recombination of the V, J, and C gene segments during B and T cell development.
• This combinatorial approach allows for a high degree of variability and specificity in immune responses, tailored to a wide array of pathogens.

Immunoglobulin Gene Diversity

• Functional immunoglobulin (Ig) genes are constructed from segments that can be combined in 200 different combinations (40 V * 5 J * 1 C).
• Heavy-chain gene combinations are even more diverse than light-chain combinations.
• Rearrangement of DNA is necessary to create a functional Ig gene during B cell development.
• Recombinase enzyme complex links one light-chain V gene segment to one J gene segment, removing the DNA between segments and forming a single exon.
• Recombinase acts randomly, meaning any V gene segment can link with any J gene segment.
• Only one allele of a light-chain gene and one allele of a heavy-chain gene undergo rearrangement in each cell.
• The rearrangements of genes are permanent, inherited by daughter cells during lymphocyte division.
• After rearrangement, the genes are transcribed and processed, leading to the translation and assembly of light and heavy chains to form antigen receptors.
• Each pair of randomly rearranged heavy and light chains results in distinct antigen-binding sites.
• The total number of antigen-binding combinations in the human B cell population is approximately 3.5 million (3.5 * 10^6).
• Mutations accrued during VJ recombination further increase the diversity of antigen-binding specificities.

Explore the fascinating mechanisms behind the generation of B cell and T cell antigen receptors. This quiz will cover how the human immune system creates a vast diversity of receptors through genetic combinations, despite the limited number of protein-coding genes. Test your understanding of this essential aspect of immunology!