S-100 is a dimeric calcium-binding protein consisting of two subunits (α and β) [61] . The β unit (S-100β) is highly brain specific, located mainly in astrocytes. Circulating levels of S-100β are elevated in patients with cerebral ischemia [62] , cardiopulmonary bypass-associated decline in explicit memory function [63, 64] , and traumatic brain injury (TBI) [65] [66] [67] . Even in mild head injury, serum levels of S-100β are correlated with clinical measures of injury severity, neuroradiologic findings, and outcomes, including postconcussion symptoms [68] . Elevated serum S-100β levels were recently demonstrated in critically ill patients with respiratory failure [69] and in porcine models of endotoxic shock [70] and acute lung injury [71] . In this latter group, elevated S-100β levels were associated with hippocampal histopathologic changes, including basophilic shrunken neurons in the pyramidal cell layer [71] . Interestingly, S-100β may have both beneficial and detrimental effects, in that lower levels may have protective neurotrophic effects, yet higher levels can lead to exacerbation of neuroinflammation and neuronal dysfunction [72] .