B Cell Light Chain Chromosome

B Cell Light and Heavy Chains

• The B cell light chain is found on chromosome 22.
• B cell light chains recombine multiple genes, specifically 2 gene segments (V and J).
• The heavy chain of a B cell is located on chromosome 14.
• Heavy chains require recombination of multiple gene segments, including V, D, and J regions.

Recombination Mechanics

• Light chains undergo somatic recombination, allowing diverse antibody generation.
• Heavy chains consist of variable (V), diversity (D), and joining (J) regions.

Antibody Characteristics

• IgM is the first antibody expressed during B cell activation.
• Membrane-bound antibodies on B cells are typically monomers of IgM.
• Monomers composed of VJ and VDJ combinations contribute to the antibody's specificity.

B Cell Characteristics

• Most B cells remain inactivated but are capable of producing antibodies upon activation.
• Light chains have a singular locus, while heavy chains have a larger diversity due to having 3 loci.
• Enzymes involved in recombination recognize specific V (variable) and J (joining) regions of both light and heavy chains.

Antibody Class Switching and Secretion

• Class switching occurs in response to antigen presence, allowing for the production of various antibody classes.
• The first antibody secreted when a B cell encounters its antigen is IgM, whereas IgG, IgE, and IgA are cleaved from the loci post-activation.

Antibody-Heavy Chain Interactions

• Any light chain can interact with any heavy chain, indicating a robust combinatorial diversity within the antibody repertoire.
• In a vaccinated individual, core antigens can elicit a stronger immune response through memory B cells.

T Cell Receptor (TCR) Specifics

• T cell receptors are heterodimers always embedded in the membrane, comprising alpha and beta chains.
• Binding regions of TCRs are located on the extracellular domains of the receptor.
• The alpha chain of TCRs contains diversity genes, enhancing specificity.

Superantigens and MHC Interaction

• Superantigens bind to MHC class II molecules, causing toxic shock syndrome.
• Endotoxic shock is instigated by bacterial lipopolysaccharides.

APC Activation and T Cell Interaction

• Activated antigen-presenting cells (APCs) express co-stimulatory molecules and MHC complexes that provide signals for T cell activation.
• CD4 helper T cells support B cells through cytokine release and co-stimulatory interactions.

MHC Molecule Structure

• MHC class I molecules possess three domains, while MHC class II molecules have two.
• The peptide binding site of MHC II is formed by the alpha-1 and beta-1 domains.
• MHC molecules are closed at their ends by structural components, ensuring stable antigen presentation.

Transplant Biology

• Individual with three HLA gene products has a likely non-typical inheritance pattern, such as a deletion or mutation.
• The rejection of transplanted tissues can occur due to mismatched MHC molecules, which activate the recipient's immune response against the transplanted tissue.