TNF and ptosis: Furthermore, activation of the immune system by LPS leads to production and release of proinflammatory cytokines such as TNF-α, IL-1β that act on the periphery and central nervous system leading to symptoms such as immobility and/or lethargy, piloerection, drowsiness, and ptosis, this symptoms are knowing as sickness behavior, which may be accompanied by physiological changes such as hypothermia.