Key takeaways

• A cytokine storm is not one disease. It is a shared pattern of hyperinflammation reached by several distinct routes, and the underlying cause determines the treatment.
• IL-6 is the central mediator in most forms, which is why IL-6 receptor blockade with tocilizumab is the specific treatment for CAR-T cytokine release syndrome.
• The defining feature is feed-forward amplification: cytokines activate cells that release more cytokines, so the response becomes self-sustaining independently of the original trigger.
• Ferritin, CRP, IL-6 and D-dimer are the markers most used to gauge severity; markedly raised ferritin is characteristic of HLH and macrophage activation syndrome.
• CAR-T cytokine release syndrome is formally graded 1 to 4 by consensus criteria based on fever, hypotension and hypoxia, and grade drives management.
• Rheumatoid arthritis and lupus do not routinely cause cytokine storms. The relevant complication is macrophage activation syndrome, an uncommon and distinct event.
• This is a research overview. It contains no dosing information and is not clinical guidance.

Contents

• What cytokines are
• What a cytokine storm is
• Why it becomes self-sustaining
• Signalling pathways involved
• The distinct entities
• CAR-T cytokine release syndrome
• COVID-19 and the debate over the term
• Cytokines and markers measured
• Treatment approaches
• Choosing ELISA kits
• Frequently asked questions

Cytokine ELISA kits

The panel covers the pro-inflammatory cytokines that drive the response, the principal anti-inflammatory counterweight, and ferritin as the severity marker.

IL-6

Human IL-6 ELISA Kit

Sandwich ELISAHuman

The central mediator, and the target of receptor blockade in cytokine release syndrome.

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TNF-α

Human TNF-alpha ELISA Kit

Sandwich ELISAHuman

An early upstream cytokine driving endothelial activation and further cytokine release.

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IL-1β

Human IL-1 beta ELISA Kit

Sandwich ELISAHuman

Inflammasome-derived; the target of IL-1 blockade in HLH and macrophage activation syndrome.

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IFN-γ

Human IFN-gamma ELISA Kit

Sandwich ELISAHuman

Central to HLH, where it drives the macrophage activation that defines the syndrome.

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IL-10

Human IL-10 ELISA Kit

Sandwich ELISAHuman

The principal anti-inflammatory cytokine — raised in storm states, but insufficient to restrain them.

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Ferritin

Human Ferritin ELISA Kit

Sandwich ELISAHuman

Markedly elevated ferritin is characteristic of HLH and macrophage activation syndrome.

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What cytokines are

Cytokines are small secreted proteins that immune cells use to signal to one another. They include the interleukins, interferons, tumour necrosis factors and chemokines, and they act by binding receptors on target cells to alter gene expression and behaviour.

Individually they are short-range and short-lived, which matters here: cytokine signalling is designed to operate locally and transiently. A storm is what happens when that locality breaks down and signalling becomes systemic and sustained.

They divide broadly into pro-inflammatory — IL-1, IL-6, TNF-alpha, IFN-gamma — and anti-inflammatory, principally IL-10 and TGF-beta. Both are elevated in a storm; the imbalance rather than the absolute level is what matters.

What a cytokine storm is

“Cytokine storm” describes a state of systemic hyperinflammation in which excessive cytokine release causes tissue damage and organ dysfunction. The term is descriptive rather than diagnostic — it names a pattern, not a single disease, and several distinct conditions produce it.

Clinically the picture includes high fever, fatigue, rash, hypotension, hypoxia and, in severe cases, multi-organ failure. Onset is often abrupt and progression can be rapid.

Because the term is used loosely, the useful question is rarely “is this a cytokine storm?” but “which entity is this?” — since that determines both the mechanism and the specific treatment.

Why it becomes self-sustaining

The defining feature is feed-forward amplification. Activated immune cells release cytokines; those cytokines activate further immune cells; those cells release more cytokines. Under normal conditions this loop is damped by anti-inflammatory signals, regulatory cells and the clearance of the original stimulus.

In a storm the loop outruns its brakes. Two consequences follow that are worth understanding:

• It becomes independent of the trigger. Removing or treating the initiating infection does not necessarily stop the response, because the inflammation is now driving itself.
• Endothelial involvement drives the organ damage. IL-6 and TNF-alpha activate endothelium, increasing vascular permeability. The resulting capillary leak produces the hypotension, oedema and hypoxia that make the condition dangerous — the damage is largely vascular rather than direct cytokine toxicity.

Signalling pathways involved

Three pathways carry most cytokine signalling, and each contributes differently rather than interchangeably.

The JAK-STAT point is the practically useful one: because IL-6 and interferons both signal through it, inhibiting JAK blocks several arms of the response simultaneously, which is why that class attracted attention during COVID-19.

The distinct entities

These conditions share a phenotype but differ in trigger, dominant cytokine and treatment.

A correction worth making explicitly: rheumatoid arthritis and systemic lupus erythematosus are sometimes described as putting patients “at risk of cytokine storms”. That overstates it. The relevant complication is macrophage activation syndrome, which is uncommon and clinically distinct — and the disease-modifying drugs used for routine RA or lupus management are not treatments for it.

CAR-T cytokine release syndrome

CRS is the best-characterised form because it is iatrogenic, expected and therefore studied prospectively. Engineered T cells engaging their target release cytokines; monocytes and macrophages respond by releasing large amounts of IL-6 and IL-1, and it is that myeloid amplification rather than the T cells themselves that produces most of the syndrome.

Onset is typically within the first few days of infusion, though it can occur up to around two weeks. Severity is graded by consensus criteria:

Tocilizumab, a monoclonal antibody against the IL-6 receptor, is approved specifically for CAR-T-associated CRS and is the targeted treatment for this entity, used with corticosteroids as required. Naming ciclosporin as the treatment for CAR-T CRS, as some sources do, is inaccurate.

A related but separate complication, immune effector cell-associated neurotoxicity syndrome, can occur with or without CRS and is graded independently.

COVID-19 and the debate over the term

Severe COVID-19 brought the term into general use, and hyperinflammation with raised IL-6, ferritin and D-dimer was clearly a feature of severe disease, contributing to ARDS.

It is worth noting honestly that the label was contested. Several comparative studies found circulating IL-6 in severe COVID-19 to be substantially lower than in classical bacterial sepsis or ARDS, which led many authors to argue that “cytokine storm” overstated what was happening and that the pathology was better described as a distinct, more localised hyperinflammatory state.

What is not disputed is that immunomodulation helped: corticosteroids improved survival in patients requiring oxygen, and IL-6 receptor blockade and JAK inhibition showed benefit in specific groups. The mechanism debate did not change the clinical direction.

Cytokines and markers measured

Measuring the pro-inflammatory and anti-inflammatory arms together is more informative than either alone, since the balance rather than the absolute concentration characterises the state.

Treatment approaches

Described here as scientific context. No dosing is given, and this is not clinical guidance — management is entirely a matter for the treating clinical team.

• IL-6 receptor blockade — tocilizumab, approved for CAR-T cytokine release syndrome and used in severe COVID-19.
• Corticosteroids — broad immunosuppression; dexamethasone improved survival in COVID-19 patients requiring oxygen.
• IL-1 blockade — anakinra, used in HLH and macrophage activation syndrome where IL-1 dominates.
• JAK inhibition — blocks signalling downstream of several cytokines at once, including IL-6 and the interferons.
• Etoposide-based protocols — specific to HLH, targeting the activated lymphocytes and macrophages driving that syndrome, rather than a general cytokine storm treatment.
• Supportive care — oxygen, fluids and organ support, which remains the foundation regardless of the specific agent used.

The theme is that specificity matters: the effective agent depends on which entity is present, which is why distinguishing them is more than an academic exercise.

Frequently asked questions