JH3

JH3 refers to the immunoglobulin heavy chain joining gene segment IGHJ3, one of the joining (J) gene segments in the human immunoglobulin heavy chain locus. This segment is part of the genetic building blocks that generate antibody diversity in B cells.

Genomic context and structure

IGHJ3 is located within the immunoglobulin heavy chain (IGH) locus on chromosome 14, in the region commonly denoted as 14q32.33. The J gene segments in this locus are short coding regions flanked by recombination signal sequences that guide the V(D)J recombination process. IGHJ3, along with other joining segments, provides the terminal portion of the variable region of the heavy chain after recombination with a variable (V) gene segment and a diversity (D) segment.

Role in V(D)J recombination

During B cell development, lymphocytes assemble a complete VDJ exon to encode the variable domain of the heavy chain. IGHJ3 contributes the last portion of this exon, determining part of the antibody’s CDR3 region, which is critical for antigen recognition. The exact amino acids contributed by IGHJ3 depend on the reading frame and junctional modifications added during recombination, including nucleotide insertions and deletions.

Expression and variation

IGHJ3 is a germline-encoded element; its usage varies among B cells and individuals. Antibody repertoire is shaped by the choice of J segments, including IGHJ3, as well as junctional diversity generated at the V–D and D–J junctions. Allelic variants and evolutionary conservation of IGHJ3 reflect its role in adaptive immunity across individuals.

See also

Immunoglobulin heavy chain locus, V(D)J recombination, antibody repertoire.

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