Cell activation is a process in which a cell is stimulated to perform a specific function or response, typically in response to a signaling molecule. This process is essential for the immune system to recognize and respond to pathogens, for cells to divide and grow, and for various other cellular functions. Cell activation can involve a variety of signaling pathways, including the binding of ligands to cell surface receptors and the subsequent activation of intracellular signaling cascades. Understanding the mechanisms of cell activation is important for developing therapeutic strategies for various diseases, such as cancer, autoimmune disorders, and infectious diseases.