What do cytokines primarily act as in the immune system?

Cytokines primarily act as signaling molecules in the immune system, facilitating communication between cells. They are proteins that are secreted by various cells in response to an immune stimulus and play a crucial role in modulating immune responses, including inflammation, cell growth, and differentiation. By binding to specific receptors on target cells, cytokines can instigate a range of biological effects, influencing the behavior of immune cells and coordinating the immune response.

Understanding cytokines as signaling molecules is essential because they are key to fostering the interactions needed for effective immune function. They guide the development and activation of immune cells, synchronize responses to infections, and help modulate the intensity and duration of immune responses. This signaling capability makes cytokines crucial in both innate and adaptive immunity, explaining their importance in immunological processes.

The other options, such as hormones, enzymes, and membrane proteins, do not accurately reflect the primary role of cytokines. While hormones also function as signaling molecules, they tend to regulate physiological processes over longer distances and timescales. Enzymes are proteins that catalyze biochemical reactions and are not specifically involved in cellular communication like cytokines. Membrane proteins can have various functions, including receptors for signaling, but they do not encapsulate the primary