Interleukin-6 (IL-6) is the primary interleukin responsible for inducing fever
IL-6 is the key pyrogenic cytokine that mediates fever through binding to IL-6 receptors on brain endothelial cells, triggering prostaglandin synthesis via the STAT3-COX-2 pathway. 1
Mechanism of IL-6-Mediated Fever
The fever response operates through a well-defined pathway:
- IL-6 binds to IL-6 receptors specifically on brain endothelial cells (not neural cells or peripheral nerves), which is essential for the febrile response 1
- This binding activates STAT3 signaling in the endothelium 1, 2
- STAT3 activation induces COX-2 expression in the hypothalamus, the brain's temperature-regulating center 1
- COX-2 produces prostaglandin E2 (PGE2), which ultimately triggers the thermoregulatory response 2
Experimental evidence demonstrates that deletion of IL-6 receptors on brain endothelial cells strongly attenuates LPS-induced fever and reduces hypothalamic COX-2 induction, while deletion of IL-6 receptors on neural cells, peripheral nerves, or sensory afferents has no effect on fever 1. Nuclear STAT3 translocation occurs in endothelial cells throughout the brain, particularly in areas surrounding sensory circumventricular organs and the median preoptic area, which are critical regions for mediating fever 2.
Role of Other Interleukins
While IL-6 is primary, IL-1β plays a contributory role in fever pathogenesis:
- IL-1β acts centrally within the hypothalamus to initiate fever 3
- Anti-IL-1β antibodies can reduce LPS-induced fever by approximately 50-60% 4
- However, IL-1β appears to work through both COX-dependent and COX-independent pathways 5
The evidence shows that blocking IL-1β action reduces but does not eliminate fever, whereas neutralizing IL-6 more substantially attenuates the febrile response 6, 4. During live bacterial infection (E. coli), central IL-6 action is crucial for fever, while IL-1 receptor antagonists have no effect 6.
Clinical Relevance
IL-1 targeted therapies are used clinically for IL-1 mediated autoinflammatory diseases that present with recurrent fever episodes, including cryopyrin-associated periodic syndromes, TNF receptor-associated periodic syndrome, and mevalonate kinase deficiency 7. These conditions involve dysregulated IL-1 signaling leading to systemic inflammation and fever.