Immune depression in polymicrobial sepsis: The role of necrotic (injured) tissue and endotoxin

Objective: Recent studies suggest immune dysfunction seen after the onset o f polymicrobial sepsis, as produced by cecal ligation and puncture (CLP), i s not caused by endotoxin (ETX) alone, but may be caused by the combined ef fect of the necrotic tissue (cecal ligation, [CL]) and other microbial comp onents. Thus, the objective of this study was to assess the ability of necr otic tissue, in the presence or absence of low-dose endotoxin, to induce ch anges in the capacity of immune cells to produce proinflammatory or anti-in flammatory cytokines approximating those seen in CLP. Design: Experimental, prospective study. Setting: A hospital laboratory in the Center for Surgical Research. Subjects: Male C3H/HeN mice. Interventions: Mice were subjected to a CL and saline infusion (CL/Sal), CL in combination with low-dose ETX infusion (CL/ETX) (0.025 mg ETX/25 g body weight/24 hrs by a peritoneally implanted osmotic mini-pump), ETX infusion alone, saline infusion alone (Sal), CLP, or sham-CLP (Sham). Splenocytes, splenic macrophage and peritoneal macrophage were harvested from these anim als 24 hrs (late) after being subjected to the above protocols. Splenocyte and macrophage inducible cytokine release was assessed by ELISA/bioassay. S urvival over a 7-day period was also examined in additional groups. Measurements and Main Results:Our results indicate a marked decrease in spl enic interleukin (IL)-2. In addition, peritoneal or splenic macrophage IL-6 productive capacity was depressed in cells from animals subjected to CL/ET X or CLP. Alternatively, CL, in the presence or absence of ETX, induced a m arked change in macrophage cytokine release capacity comparable to that see n in CLP, ie, decreased IL-12 release and increased IL-10 secretion. To the extent these cellular alterations contribute to an increase in mortality r ate, we observed in subsequent survival studies that neither CL alone nor E TX produced mortality. However, the combination of CL/ETX markedly increase d 7-day mortality rate (similar to 33%), although not to the same extent as CLP (80%). Conclusions: These results collectively suggest that the response to devita lized tissue produced by cecal ligation may predispose the host to the indu ction of a suppressive macrophage phenotype. The subsequent exposure of the se animals to microbial agents induces immune dysfunction, as well as morta lity seen after such a polymicrobial septic challenge.