A cytokine storm is the systemic expression of a healthy and vigorous immune system resulting in the release of more than 150 inflammatory mediators (cytokines, oxygen free radicals, and coagulation factors). Both pro-inflammatory cytokines (such as Tumor Necrosis Factor-alpha, InterLeukin-1, and InterLeukin-6) and anti-inflammatory cytokines (such as interleukin 10, and interleukin 1 receptor antagonist) are elevated in the serum, and the fierce and often lethal interplay of these cytokines is referred to as a "Cytokine Storm". The primary contributors to the cytokine storm are TNF-a (Tumor Necrosis Factor-alpha) and IL-6 (Interleukin-6). The cytokine storm is an inappropriate (exaggerated) immune response that is caused by rapidly proliferating and highly activated T-cells or natural killer (NK) cells. These cells are themselves activated by infected macrophages. The cytokine storm must be treated and suppressed or lethality can result.