Understanding Memory B Cell Selection

The mammalian adaptive immune system has evolved over millions of years to become an incredibly effective defense against foreign antigens. The adaptive immune system's humoral response creates plasma B cells and memory B cells, each with their own goals. The affinity maturation process is widely viewed as a heuristic to solve the global optimization problem of finding B cells with high affinity to the antigen. However, memory B cells appear to be purposely selected earlier in the affinity maturation process and have lower affinity. We propose that this memory B cell selection process may be a heuristic solution to two expected risk optimization problems: optimizing for affinity to similar antigens in the future despite mutations or other minor differences, and optimizing to warm-start future plasma B cell training. We use simulations to provide evidence for our hypotheses, taking into account data showing that certain B cell mutations are more likely than others.