Cytokine release syndrome (CRS) is a form of systemic inflammatory response syndrome (SIRS) that can be triggered by a variety of factors such as infections and certain drugs. It refers to cytokine storm syndromes (CSS) and occurs when large numbers of white blood cells are activated and release inflammatory cytokines, which in turn activate yet more white blood cells. CRS is also an adverse effect of some monoclonal antibody medications, as well as adoptive T-cell therapies. When occurring as a result of a medication, it is also known as an infusion reaction.
The term cytokine storm is often used interchangeably with CRS but, despite the fact that they have similar clinical phenotype, their characteristics are different. When occurring as a result of a therapy, CRS symptoms may be delayed until days or weeks after treatment. Immediate-onset CRS is a cytokine storm, although severe cases of CRS have also been called cytokine storms.
Symptoms include fever that tends to fluctuate, fatigue, loss of appetite, muscle and joint pain, nausea, vomiting, diarrhea, rashes, fast breathing, rapid heartbeat, low blood pressure, seizures, headache, confusion, delirium, hallucinations, tremor, and loss of coordination.
Lab tests and clinical monitoring show low blood oxygen, widened pulse pressure, increased cardiac output (early), potentially diminished cardiac output (late), high levels of nitrogen compounds in the blood, elevated D-dimer, elevated transaminases, factor I deficiency and excessive bleeding, higher-than-normal level of bilirubin.
CRS occurs when large numbers of white blood cells, including B cells, T cells, natural killer cells, macrophages, dendritic cells, and monocytes are activated and release inflammatory cytokines, which activate more white blood cells in a positive feedback loop of pathogenic inflammation. Immune cells are activated by stressed or infected cells through receptor-ligand interactions.