What is the role of cytokines?

• A. They Identify Substances as Foreign and Produce Antibodies.
• B. They Coat an Invading Microorganism and Prevent It from Penetrating Healthy Cells.
• C. They Initiate the Innate Immune Response to a Substance Recognized as Nonself.
• D. They Transmit Information about the Presence of a Foreign Substance from a Receptor Molecule to Other Molecules and Cells of the Immune System.

Answer: (D)

Signaling within the immune system relies on cytokines, small proteins released by immune cells after detecting a pathogen. They act as messengers that convey information about the presence of a foreign substance to other cells, helping coordinate the response. Cytokines bind to specific receptors on target cells and can influence their behavior—promoting inflammation, recruiting immune cells, activating macrophages, or guiding T and B cell differentiation—so they serve as the communication network that links detection to action across the immune system. This signaling role is why this statement is the best fit: cytokines transmit information from the initial detection event to other molecules and cells to shape the overall response. They do not themselves identify foreign substances (that’s the job of antibodies), coat invaders for protection (opsonization), or initiate innate defense on their own (recognition by pattern‑recognition receptors triggers the innate response, with cytokines amplifying and directing that response).