• Xin Huang, Fabienne Venet, Yvonne L Wang, Alain Lepape, Zhenglong Yuan, Yaping Chen, Ryan Swan, Hakim Kherouf, Guillaume Monneret, Chun-Shiang Chung, and Alfred Ayala.
• Division of Surgical Research, Department of Surgery, Brown University School of Medicine/Rhode Island Hospital, 593 Eddy Street, Providence, RI 02903, USA.
• Proc. Natl. Acad. Sci. U.S.A. 2009 Apr 14; 106 (15): 6303-8.

AbstractSepsis, a leading cause of death worldwide, involves concomitant expression of an overzealous inflammatory response and inefficient bacterial clearance. Macrophage function is pivotal to the development of these two aspects during sepsis; however, the mechanisms underlying these changes remain unclear. Here we report that the PD-1:PD-L pathway appears to be a determining factor of the outcome of sepsis, regulating the delicate balance between effectiveness and damage by the antimicrobial immune response. To this end we observed that PD-1(-/-) mice were markedly protected from the lethality of sepsis, accompanied by a decreased bacterial burden and suppressed inflammatory cytokine response. To the extent that this is a macrophage-specific aspect of the effects of PD-1, we found the following: first, peritoneal macrophages expressed significantly higher levels of PD-1 during sepsis, which was associated with their development of cellular dysfunction; second, when peritoneal macrophages were depleted (using clodronate liposomes) from PD-1(-/-) mice, the animals' bactericidal capacity was lowered, their inflammatory cytokine levels were elevated, and protection from septic lethality was diminished; and third, blood monocytes from both septic mice and patients with septic shock shared markedly increased PD-1 levels. Together, these data suggest that PD-1 may not only be a dysfunctional marker/effector of macrophages/monocytes, but may also be a potential therapeutic target for designing measures to modulate the innate immune response, thereby preventing the detrimental effects of sepsis.

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