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 immunological objectives. 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 an approximate solution to two optimization problems: optimizing for affinity to similar antigens in the future despite mutations or other minor differences, and optimizing to warm start the generation of plasma B cells in the future. We use simulations to provide evidence for our hypotheses, taking into account data showing that certain B cell mutations are more likely than others. Our findings are consistent with memory B cells having high-affinity to mutated antigens, but do not provide strong evidence that memory B cells will be more useful than selected naive B cells for seeding the secondary germinal centers.

哺乳动物适应性免疫系统经过数百万年的进化，已成为抵御外来抗原的极其有效的防御系统。适应性免疫系统的体液反应产生血浆 B 细胞和记忆 B 细胞，每个细胞都有自己的免疫目标。亲和力成熟过程被广泛认为是解决寻找对抗原具有高亲和力的 B 细胞的全局优化问题的启发式方法。然而，记忆 B 细胞似乎是在亲和力成熟过程中较早地被有意选​​择并且具有较低的亲和力。我们提出，这种记忆 B 细胞选择过程可能是两个优化问题的近似解决方案：尽管存在突变或其他细微差异，但优化未来对类似抗原的亲和力，以及优化未来热启动血浆 B 细胞的生成。我们使用模拟来为我们的假设提供证据，同时考虑到数据显示某些 B 细胞突变比其他细胞突变的可能性更大。我们的发现与对突变抗原具有高亲和力的记忆 B 细胞一致，但没有提供强有力的证据表明记忆 B 细胞比选定的幼稚 B 细胞更有用，可用于接种次级生发中心。