句子如何翻译？

The reason that only antibodies with bound antigens activate effector mechanisms is that two or more adjacent antibody Fc portions are needed to bind to and trigger various effector systems, such as complement proteins and Fc receptors of phagocytes

只有结合抗原的抗体激活效应机制的原因是需要两个或多个相邻的抗体Fc部分来结合和触发各种效应系统，如补体蛋白和吞噬细胞的Fc受体。

问题：句子如何翻译？，一定要“两个或多个相邻的抗体Fc部”，一个抗体Fc部不行吗？。