T-helper cells are a type of white blood cell that play a crucial role in the immune system. They help coordinate the body's response to infections by signaling other immune cells, such as B cells and cytotoxic T cells, to take action against pathogens. These cells are characterized by the presence of the CD4 protein on their surface, which distinguishes them from other T cells. When activated by recognizing specific antigens presented by antigen-presenting cells, T-helper cells release cytokines that enhance the immune response, ensuring the body effectively fights off infections and diseases.