Which is not a pyrogen -

Pyrogenic cytokines, such as interleukin (IL)-1b, IL-6, and tumor necrosis factor-a, which result from stimulated mononuclear phagocytes, interact directly with the anterior hypothalamus, which coordinates thermoregulation through a hierarchy of neural structures. Prostaglandin E2 is a proximal mediator in the preoptic-anterior hypothalamic area. Direct neural pathways from the periphery to the brain also may be involved.2 Exogenous pyrogens including bacterial cell wall products may act on Toll-like receptors in the hypothalamus and elevate the thermoregulatory setpoint Ref Davidson 23rd edition pg 1301