V(d)j Annotation

Computational assignment begins by aligning each receptor sequence with germline reference genes. The alignment supports separate calls for the V, D, and J segments, while sequence differences near their joins help identify junctional regions. This approach converts raw receptor sequence information into annotations that can be compared across immune-repertoire datasets and used to examine receptor composition.

CDR3 is important because it contains junctional sequence variation created through nucleotide additions and deletions. These changes can distinguish receptors that use related gene segments while contributing to differences in antigen recognition. Examining CDR3 alongside V, D, and J assignments therefore provides a more informative view of receptor diversity than segment calls alone.

Nucleotide additions and deletions alter the sequence at the junctions between assigned gene segments. Consequently, researchers must interpret these regions as part of the annotation rather than treating the germline V, D, and J segments as the complete receptor sequence. The resulting junctional information helps explain sequence variation and supports comparison of receptor clonotypes.

The resulting annotations show which germline segments contribute to immunoglobulin or T-cell receptor sequences and describe variation in their junctional regions. Researchers can use these features to profile an immune repertoire, identify related receptor sequences, and follow clonotypes across samples. This connects sequence-level patterns with changes in immune-cell populations during infection, vaccination, or disease.

A typical workflow starts with receptor sequences, aligns them to germline reference genes, assigns the contributing V, D, and J segments, and then characterizes the junctional regions, including CDR3. The completed annotations can be organized for repertoire profiling or clonotype tracking. Their value depends on retaining both segment assignments and the sequence variation at the joins.

In immunology and infection studies, annotated receptor sequences help researchers examine responses associated with pathogens, vaccines, or disease. Comparing segment usage, junctional regions, and clonotypes can reveal patterns of receptor expansion or change across samples. For both immunoglobulin and T-cell receptor data, these results help relate immune-repertoire variation to antigen recognition.