Cell surface markers are specific proteins or molecules found on the outer membrane of cells. They play a crucial role in identifying and differentiating various cell types, such as immune cells, stem cells, and cancer cells. These markers help the body recognize its own cells and distinguish them from foreign invaders, like bacteria and viruses. These markers can be used in medical diagnostics and research. For example, flow cytometry is a technique that analyzes cell surface markers to determine the characteristics of different cell populations. Understanding these markers is essential for developing targeted therapies and improving treatments for diseases like cancer.