What is the action of cytokines in terms of hematopoiesis?

Cytokines play a crucial role in the regulation of hematopoiesis, which is the process of blood cell production originating from hematopoietic stem cells in the bone marrow. The correct choice highlights that cytokines are signaling molecules that help modulate the development, differentiation, and proliferation of various blood cells, including red blood cells, white blood cells, and platelets.

During hematopoiesis, specific cytokines activate or inhibit the activity of progenitor cells, guiding them to mature into the required types of blood cells depending on the body's needs. This regulation ensures that an adequate and balanced supply of blood cells is maintained, which is essential for functions such as oxygen transport, immune responses, and wound healing.

In contrast to stopping blood cell production or being limited to situations of infection, the primary function of cytokines is to maintain and regulate hematopoiesis under normal and pathological conditions. Therefore, their role is fundamental in increasing or decreasing the production of blood cells as necessary, which is accurately reflected in the answer regarding the regulation of blood cell production.