Cytokine storm (hypercytokinemia)

Mechanism and key mediators

Cytokines are small proteins produced by immune and other cells to coordinate host defenses; examples include interleukins, tumor necrosis factor (TNF) and interferons. In a cytokine storm, cytokine production and immune cell activation form a positive feedback loop: cytokines recruit and activate leukocytes, which in turn secrete more cytokines, driving escalating systemic inflammation. For background on the signaling molecules involved, see cytokines and for immune system context see immune system.

Causes and common triggers

Several conditions can trigger cytokine storms. Severe infections—viral, bacterial or fungal—are frequent causes. Some viral outbreaks have been closely associated with hyperinflammatory responses, and maladaptive immune activation can also arise during certain cancers, after some immunotherapies (for example CAR T‑cell therapy), and in genetic or rheumatologic syndromes such as hemophagocytic lymphohistiocytosis (HLH) and macrophage activation syndrome (MAS).

Clinical features, diagnosis and complications

Presentation ranges from high fever and profound fatigue to rapid respiratory decline, low blood pressure, clotting abnormalities and organ dysfunction. Laboratory findings commonly show elevated inflammatory markers and high circulating cytokines, though these measurements are not always available in routine practice. Clinicians diagnose cytokine storm by combining clinical signs, laboratory evidence of systemic inflammation and exclusion of alternative causes. Major complications include ARDS, shock, coagulation disorders and long‑term organ damage.

Treatment approaches

Management combines supportive critical care with therapies that reduce immune overactivity. Supportive measures address respiratory failure, hemodynamic instability and secondary infections. Immunomodulatory strategies may include corticosteroids, selective cytokine blockers (for example therapies targeting interleukin‑6), and other targeted agents or plasma exchange in selected cases. The choice of therapy depends on the underlying trigger, severity and evolving evidence; outcomes improve with early recognition and appropriate supportive care.

Historical examples and significance

Cytokine storms have been implicated in several notable outbreaks and clinical scenarios. Historical analyses suggest an important role in the high mortality among otherwise healthy young adults during the 1918 influenza pandemic. Research into the severe acute respiratory syndrome (SARS) epidemic of 2003 found evidence that overactive immune responses contributed to fatalities (see studies from Hong Kong: research report and material on SARS). More recent epidemics and some cases of severe COVID‑19 also prompted renewed study of hyperinflammation, though the precise contribution varies by disease and patient.

Distinctions and notable facts

• Cytokine storm is a descriptive term rather than a single disease; it overlaps with syndromes such as sepsis‑related cytokine release, HLH and MAS.
• Not every severe infection produces a cytokine storm; host factors, pathogen characteristics and timing all influence whether hyperinflammation develops.
• Because therapies that suppress immunity can increase infection risk, treatment requires careful balancing of benefits and harms and is often tailored to the clinical context.

Awareness of cytokine storm is important for clinicians and researchers because early recognition and targeted intervention can alter outcomes. Ongoing research aims to clarify biomarkers that reliably identify patients who will benefit from specific immunomodulatory therapies and to refine safe, effective treatment protocols.