Which of the following is NOT a mediator of inflammation?

Cytokines are indeed important signaling molecules in the immune response and play a critical role in the regulation of inflammation. However, they can also be classified in various contexts, as they may not act as direct mediators of inflammation compared to other options listed.

Bradykinin, histamine, and prostaglandins are all well-established mediators of the inflammatory response. Bradykinin is a peptide that promotes vasodilation and increases vascular permeability, contributing to the classic signs of inflammation. Histamine, released from mast cells, also enhances vascular permeability and causes vasodilation, leading to redness and swelling. Prostaglandins are lipid compounds that mediate various aspects of inflammation, including pain and fever, and help in regulating the inflammatory response.

Considering these roles, the selection indicates that while cytokines are associated with inflammation, they do not serve as direct mediators in the same way as bradykinin, histamine, and prostaglandins. This distinction leads to the correct answer identifying cytokines as the option that is not a direct mediator of inflammation in the traditional sense.