Which of the following is a characteristic of T-helper cells?

T-helper cells, also known as CD4+ T cells, play a crucial role in the immune response by stimulating other immune cells. They do not act directly to kill infected cells or produce antibodies themselves; rather, their primary function is to coordinate the immune response. T-helper cells release cytokines, which are signaling molecules that enhance the activity of various immune cells, including B cells (which produce antibodies) and cytotoxic T cells (which kill infected or cancerous cells).

This stimulation is vital for a robust and effective immune response, as it ensures that various components of the adaptive and innate immune systems work together synergistically to eliminate pathogens and infected cells. The other choices describe functions associated with different aspects of the immune system, such as cytotoxic T cells being responsible for directly killing infected cells, while regulatory T cells may suppress immune responses. Therefore, the stimulation of other immune cells is the fundamental and defining characteristic of T-helper cells.