I use real cells, meaning that they came from a living organism originally. That being said, most of the cells that I use in the laboratory were from a tumor or were treated in a way that makes them immortal. That makes it a lot easier for us to grow them and do experiments on them, because we can grow a lot of them to get larger sample sizes (it’s hard to detect something in one cell) without having to get them from an animal or human every time. Also, using these cells (called cell lines) lets us compare different treatments (for example infected or uninfected cells) without having to worry about different genetics from different cells affecting our experiments (this would happen if you compared two different cells from two different people- the experiment would be messy because you couldn’t control all of the differences in the DNA of each cell from each person). You can read more about cell culture here: https://www.coriell.org/research-services/cell-culture/what-is-cell-culture
I’ve also used cells isolated from mosquitoes and other animals. The lab that my husband worked in actually grew mosquitoes and kept them in a little cage so they could infect them with viruses and study them. We worked together on a project where he did mosquito experiments and I did cell culture experiments to see how West Nile virus changes the mosquito and human cell immune response – it was really fun to work together!