BCR selection and affinity maturation in Peyer's patch germinal centres.

Area of Science:

• Immunology
• Microbiology
• Genetics

Background:

• B cell receptors (BCR) and antibodies are crucial for immune responses, with their diversity generated by V(D)J recombination.
• Germinal centers (GCs) are sites of B cell maturation, but chronic GCs in Peyer's patches (PPs) and their BCR repertoires remain poorly understood.
• Gut microbiota significantly impacts intestinal immunity, including the development of PPs.

Purpose of the Study:

• To elucidate the physiological BCR repertoires and somatic hypermutation patterns in mouse PP GCs.
• To investigate the role of gut microbiota in shaping BCR repertoires within PPs.
• To understand the selection mechanisms and affinity maturation processes in chronic PP GCs.

Main Methods:

• High-throughput sequencing to analyze V(D)J segment usage and somatic hypermutation profiles in mouse PP GCs.
• Comparative analysis of BCR repertoires in mice with and without specific gut microbiota.
• Fecal microbiota transfer experiments from specific-pathogen-free to germ-free mice.

Main Results:

• Mouse PP GCs expand public BCR clonotypes with canonical CDR3s, frequently observed due to junctional biases in V(D)J recombination.
• Some public clonotypes are microbiota-dependent and encode antibodies reactive to bacterial glycans, while others are independent.
• Fecal transfer restored germ-dependent clonotypes, directly implicating BCR selection by gut microbiota. Recurrent somatic hypermutations indicate affinity maturation in PP GCs.

Conclusions:

• Persistent gut antigens select recurrent BCR clonotypes, seeding chronic PP GC responses.
• Gut microbiota plays a critical role in shaping BCR repertoires and immune responses in Peyer's patches.
• Affinity maturation occurs in mouse PP GCs under homeostatic conditions, driven by antigen selection.