Re-evaluating the recycling hypothesis in the germinal centre

Area of Science:

• Immunology
• Computational Biology
• Theoretical Biology

Background:

• Germinal center (GC) reactions are crucial for adaptive immunity, particularly for antibody affinity maturation.
• The hypothesis of B cell recycling within GCs has been proposed to explain observed affinity maturation.
• Previous theoretical models seldomly compared with experimental data, leaving the role of recycling unresolved.

Purpose of the Study:

• To propose and test a mathematical model of GC reactions that does not include B cell recycling.
• To investigate if selection mechanisms, previously uncovered experimentally, are sufficient to explain affinity maturation without recycling.
• To compare model predictions with experimental data from specific immune responses.

Main Methods:

• Development of a mathematical model for GC reactions excluding B cell recycling.
• Incorporation of experimentally validated selection mechanisms into the model.
• Application of the model to diverse experimental systems and comparison with experimental data on antibody affinity maturation.

Main Results:

• The model without recycling successfully explains the observed affinity maturation levels in a primary immune response to (4-hydroxy-3-nitrophenyl)-acetyl.
• Similar affinity maturation levels were achieved for other immune responses.
• The model's prediction for antibodies with multiple affinity-enhancing mutations was significantly lower than observed experimental data.

Conclusions:

• B cell recycling is not a necessary mechanism to achieve the observed levels of affinity maturation in all GC reactions.
• The proposed model, incorporating specific selection mechanisms, provides a viable alternative explanation for antibody affinity maturation.
• Further investigation is needed to reconcile model predictions with experimental data for complex affinity maturation scenarios involving multiple mutations.