HMGB1 is a non-histone DNA-binding protein that serves as a structural component to facilitate the assembly of nucleoprotein complexes in the nucleus [14] . Extracellularly, HMGB1 functions as a cytokine. In response to infl ammatory stimuli, including PAMPs, HMGB1 can be actively released into the extracellular environment from a variety of cells including monocytes, macrophages, endothelial cells, enterocytes, pituicytes, dendritic cells, and natural killer cells [14] . HMGB1 can also be passively secreted into the extracellular milieu when cells die in a non-programmed way (necrosis), whereas apoptotic cells modify their chromatin so that HMGB1 binds irreversibly and consequently is not released [4] . During infectious diseases, increased HMGB1 concentrations may be due to active as well as passive release. Detection methods of HMGB1 that are currently used (and published) do not distinguish between these (and possible other) diff erent forms of HMGB1. More studies are necessary to: 1) Report the biological activity of (diff erent forms of ) HMGB1; and 2) develop HMGB1 ELISA assays that can distinguish between these (possibly also functionally) diff erent forms of HMGB1. Most investigations on HMGB1 and infection involve sepsis, the second leading cause of death in non-coronary intensive care units (ICUs) and the 10 th leading cause of death overall. Patients with severe sepsis display elevated circulating HMGB1 levels [15] [16] [17] and HMGB1 is predominantly released at the site of infection; patients with pneumonia and those with peritonitis showed increased concen trations in fl uid obtained from the bronchoalveolar space and abdomen, respectively [17] . In an animal model of CLP-induced sepsis, the kinetics of HMGB1 secretion in vivo was delayed and more sustained when compared with the release of pro-infl ammatory cytokines, like TNF-α, IL-1β and IL-6 [18, 19] . Similarly, various interventions that inhibit HMGB1 activity or production, such as anti-HMGB1 antibodies, the A-box segment of HMGB1, ethyl pyruvate, and nicotine, reduced CLPinduced sepsis and/or LPS lethality even if treatment was delayed for many hours, up to one day after the challenge [20, 21] . An implicated crucial event in sepsis pathophysio logy is apoptosis of immune cells, playing a major role in immunosuppression and lethality [22] . HMGB1 seems to be a downstream factor of apoptosis in the fi nal common pathway to organ damage in severe sepsis as indicated by observations that prevention of lymphocyte apoptosis improved survival after CLP [23] , whereas anti-HMGB1 treatment reduced lethality in the same model without infl uencing apoptosis [19] . Th is indicates that HMGB1 secretion is a relatively late event in sepsis that contributes signifi cantly to a worsened outcome. In addition, it has been reported that very pure HMGB1 does not have cytokine-inducing capacity itself, but activates cells indirectly by fi rst acquiring immune stimulating CpG DNA [24] , which is released in the bloodstream during bacterial sepsis. However, a recent study reported that HMGB1-mediated induction of macrophage cytokine production requires binding to TLR4, and that binding and signaling are dependent on a molecular mechanism that requires cysteine in position 106 within the B box [25] . Together these data indicate that HMGB1 may exert pro-infl ammatory eff ects in a direct TLR4-dependent way and an indirect way via binding of DAMPs and other agonistic molecules. S100A12 S100A12 is a calcium binding protein expressed in the cytoplasm of neutrophils, where it comprises 5% of the total protein content. Furthermore, S100A12 -also known as EN-RAGE (extracellular newly identifi ed ligand of RAGE) or myeloid-related protein (MRP)-6 -is found in monocytes and lymphocytes and provokes pro-infl ammatory responses in endothelial cells [26] . Although many RAGE ligands are promiscuous with regard to receptor use, S100A12 has only been shown to bind to RAGE. S100A12 expression is high in infl ammatory diseases such as atherosclerosis, rheumatoid arthritis, Crohn's disease, Kawaski disease, and cystic fi brosis. Within the lungs, S100A12 and RAGE are increased during acute lung injury (ALI) [26] . S100A12 expression may refl ect activation of neutrophils during pulmonary infl ammation and may contribute to endothelial activation via binding to RAGE [26] .