Immune cells use active tugging forces to rank affinity and accelerate evolution

Generation of potent antibodies relies on positive selection of immune B cells expressing high affinity receptors. Effective selection during B cell affinity maturation (a rapid evolutionary process) requires efficient ranking of affinities. Yet, the mechanism by which affinity discrimination is achieved and how it affects B cell evolution remains unclear. Growing evidence shows that B cells use mechanical forces to actively extract antigens from the surface of antigen-presenting cells. Here we study the stochastic process of antigen extraction using theory and simulations. We find that application of mechanical force alters the energy landscape of molecular interactions and consequently extends the range of distinguishable affinities. Integrating molecular extraction with population dynamics, we demonstrate that B cells may expend mechanical energy to accelerate affinity maturation.