Th1, or T helper 1 cells, are a type of immune cell that play a crucial role in the body's defense against infections. They are part of the adaptive immune system and help activate other immune cells, such as macrophages and cytotoxic T cells, to fight off pathogens, particularly viruses and certain bacteria. Th1 cells produce specific signaling molecules called cytokines, which enhance the immune response. These cells are primarily generated from naive T cells in response to specific signals, including the presence of certain antigens and the influence of cytokines like interleukin-12. Th1 cells are essential for maintaining a balanced immune response, as an overactive Th1 response can lead to autoimmune diseases, while an underactive response can result in increased susceptibility to infections.