What is the primary action of cytokines in cell signaling?

Cytokines play a crucial role in cell signaling by altering the behavior of neighboring cells. These small proteins are secreted by various cells in the immune system and can influence the immune response, inflammation, and cell communication. By binding to specific receptors on target cells, cytokines can stimulate or inhibit processes such as cell growth, differentiation, and function. This ability to modulate the activity of adjacent cells makes them integral to coordinating responses during immune challenges, tissue repair, and various physiological processes.

The other options, while involving important biological functions, do not encompass the primary action of cytokines. Apoptosis, hormone secretion, and cellular respiration are distinct processes that are not directly regulated by cytokines in the same manner as cell-to-cell communication.