Seimei no Kagaku: Micro Patrol

Both are shows about human body, with anthropomorphized cells as characters. While Hataraku Saibou usually focuses on how the body fights against threats in more action-oriented manner and with very anime presentation, Micro Patrol explains how human body works more thoroughly, is more cartoony, educational and aimed at children. 

They take place in a human body, where cells work together to fight viruses, repair the body and transport oxygen. They both teach you some useful stuff about the cells and what's going on in the human body. Hataraku Saibou just does it in a more anime-feeling way, while Seimei is meant more for kids. They are really similar, but if you enjoyed Hataraku Saibou, you shouldn't really go watch Seimei, I'm just putting it out there. 

We have anthropomorphic cells that run through your body and the both shows explains in a fun interactive way a bit how your body works. If you liked Hataraku Saibou (Cells at Work!) you could enjoy Seimei no Kagaku: Micro Patrol, no doubt. I've seen Seimei no Kagaku: Micro Patrol (aka. "Once Upon a Time... Life") dubbed in my mothers tounge back in the day when I was a kid not only once, but twice.