If you looked later, as the antibody production response matures, some IgG is produced so that in the late period after initial priming you'd have a mixture of IgM and IgG in the blood.

如果你稍后再观察,等到产生抗体的应答趋于成熟后,就会产生一些IgG抗体,在初次免疫的最终阶段,你的血液中有IgM,和IgG两种抗体

生物医学工程探索课程节选 : 耶鲁公开课