What is cytokine release syndrome?

Cytokine release syndrome or CRS is an acute systemic inflammatory syndrome. It occurs when the immune system reacts too aggressively to an infection, over activating the T cells and other immune cell types, which then release excessive amounts of cytokines into the bloodstream. The abnormally high cytokine levels in the blood cause dangerous levels of inflammation throughout the body, disrupting normal body functions. 

Cytokine release syndrome is characterized by fever and multiple organ dysfunction and is a potentially life-threatening condition. The type and severity of the symptoms vary widely depending on the infection. 

Besides occurring due to a pathologic infection, it may also occur as a result of some types of immunotherapy.