Somatic hypermutation generates antibody specificities beyond the primary repertoire.

Area of Science:

• Immunology
• Molecular Biology
• Adaptive Immunity

Background:

• Antibody affinity maturation is crucial for adaptive immunity, primarily occurring via somatic hypermutation (SHM) and selection in germinal centers (GCs).
• The extent to which SHM can generate novel antibody specificities beyond the primary repertoire established by V(D)J recombination remains an area of investigation.

Purpose of the Study:

• To investigate if B cell somatic hypermutation (SHM) can generate new antibody specificities beyond those encoded by the V(D)J recombination.
• To explore the role of B cell competition in limiting the emergence of new antibody-antigen interactions during SHM.

Main Methods:

• Tracking pre-defined non-specific B cells in various immunization models.
• Utilizing phylogenetic analyses to trace mutational pathways of antibody evolution.
• Assessing the impact of enhanced T cell co-stimulation on new antigen recognition.

Main Results:

• Non-cognate B cells within GCs undergo SHM, leading to the generation of de novo antigen recognition.
• Limited B cell competition facilitates the emergence of new antigen affinities and recognition of multiple epitopes.
• Diverse mutational pathways were identified, and T cell co-stimulation promoted novel antigen recognition.

Conclusions:

• B cell competition, not an intrinsic requirement for pre-existing affinity, limits the generation of new antibody specificities through SHM.
• The adaptive immune system demonstrates flexibility, with SHM capable of reshaping antibody specificity beyond the primary V(D)J repertoire.
• This highlights a broader capacity for antibody-antigen interaction exploration than previously understood.