QS401. OVER-EXPRESSION OF IL-18 BINDING PROTEIN NEUTRALIZES THE NEGATIVE EFFECTS OF IL-18 ON CELL PROLIFERATION AND APOPTOSIS IN MESENCHYMAL STEM CELLS. Meijing Wang, Kirstan Meldrum, Paul Crisostomo, Troy Markel, Liping Du, Keith D. Lillemoe, Daniel R. Meldrum; Indiana University, Indi- anapolis, IN Introduction: Stem cells are a potent promising therapy for mul- tiple diseases. Interestingly, it remains unclear how to best ex- pand stem cells ex vivo, whereas to keep their abilities of self- renewal and un-differentiation in vitro. Engineering stem cells is a possible creating so called “super stem cells”. Interleukin 18 (IL-18) has been reported to play an antiangiogenic role in cul- tured tumor cells and bone marrow derived endothelial progenitor cells. However, it is unknown what role IL-18 plays in stem cell proliferation and apoptosis, and by what mechanisms. We hypoth- esized that 1) IL-18 will inhibit mesenchymal stem cell (MSC) proliferation and induce apoptosis; 2) MSCs from transgenics (Tg) that over-express IL-18 binding protein (IL-18BP) will exhibit improved proliferation and apoptosis in response to IL-18 by in- creasing ERK activation. Methods: MSCs from wild type (WT) and IL-18-BP Tg mice were plated (triplicates/group) and divided into control and IL-18 group. After 24- or 48-hours, cell prolifer- ation was analyzed by using 5-Bromo-2’-deoxy-uridine labeling and detection kit III, and apoptosis was performed by cell death detection ELISA. During 15 min, 30 min, 1 hour, 2 hours, 4 hours, 6 hours and 24 hours of IL-18 treatment, activation of ERK was confirmed in cell lysate via Western blot. p0.05= statistically significant with t-test. Results: IL-18 decreased MSC prolifera- tion from 0.93+/-0.03 to 0.77+/-0.06 (absorbance at 405nM) in WT, whereas IL-18BP overexpression neutralized this negative effect of IL-18 on cell proliferation (control 0.77+/-0.03 vs. IL-18 0.86+/-0.07). Additionally, administration of IL-18 for 24 hours and 48 hours significantly increased cell apoptosis by 27% and 22% in WT. However, there was no increased apoptosis noted in IL-18 treated IL-18BP Tg MSCs. Interestingly, western blots showed that IL-18 transiently elevated ERK activation at 1 hour and 2 hours in WT, while increased ERK activation was observed at 15 min after administration of IL-18 and maintained high levels of p-ERK until 6 hours in IL-18BP Tg. ERK activation was back to normal in both WT and IL-18BP Tg after 24 hours. Conclusions: 1) IL-18 appears to inhibit MSC proliferation and to increase apoptosis; 2) IL-18BP overexpression neutralized the negative effects of IL-18 on MSC proliferation and apoptosis likely through ERK signal. Understanding the mechanisms of IL-18 may allow engineering MSC to maximize therapeutic benefit. QS402. IL-6 SYNERGIZES WITH T HELPER II CYTOKINES TO UP-REGULATE ARGINASE I IN SPLEEN MY- ELOID SUPPRESSOR CELLS FOLLOWING TRAU- MATIC STRESS. Petar J. Popovic, Yoram Vodovotz, Sid- ney M. Morris, Jr., Veronica Munera, Juan B. Ochoa; University of Pittsburgh Medical School, Pittsburgh, PA Introduction: Accidental or surgical traumatic stress causes im- mune dysfunction associated with increased infection rates and high morbidity and mortality. We have recently demonstrated that trauma-induced immature myeloid suppressor CD11b + /Gr-1 + cells (TIIMSC) accumulate in the spleen, expressing high levels of arginase I and causing T-cell dysfunction by depleting L-arginine. Factors that might lead to increased arginase activity in splenic CD11b + /Gr-1 + cells after trauma are not known. Methods: Plasma was harvested from mice at different time points after trauma and cytokine levels were quantified using luminex assay. CD11b + /Gr-1 + cells were harvested from the spleens and cultured in the presence of IL-4, IL-5, IL-6, IL-10, IL-13 and TGF-. Argi- nase activity was measured through a colorimetric assay. Results: In this report we provide evidence that IL-6 and IL-5 are both temporarily increased in the blood after trauma (IL-6, 17991pg/ ml, peak at 3h; IL-5, 11064pg/ml, peak at 12h). In contrast to the known stimulatory effects of IL-4 and IL-13, neither IL-5 nor IL-6 induced arginase activity in splenic CD11b + cells. However, IL-6 induced a significant additional increase in arginase I expression and activity in combination with low doses of either IL-4 (2266312 vs. 35439, p0.01) or IL-13 (1955293 vs. 26041, p0.01). This synergistic induction of arginase was much more potent than the effect of two other known arginase-inducing cy- tokines, IL-10 (77681) and TGF- (59466). IL-5 not only failed to synergize with either IL-4 or IL-13, but in fact antagonized the stimulatory activity of IL-6. Injection of IL-6 in control animals resulted in a modest increase in both arginase activity and sensi- tivity to IL-4 and IL-13 in splenic CD11b + cells, but failed to reach the levels induced by trauma. Finally, detected plasma IL-6 level positively correlated (R 2 =0.903) with the increase in arginase activity in spleen CD11b+ cells. Conclusion: Our results define a novel role for IL-6 after trauma, suggesting that this cytokine is necessary but not sufficient for arginase increase in spleen CD11b + /Gr-1 + cells. By influencing arginase I activity in TIIMSC, IL-6 plays an important role in creating trauma induced immune deficiency. QS403. HEME OXYGENASE-1 UP-REGULATION IN MACRO- PHAGES REDUCES STIMULATED CYTOKINE SECRE- TION. Jonathan P. Roach 1 , David A. Partrick 2 , Ernest E. Moore 3 , Sagar S. Damle 1 , Chris C. Silliman 1 , Robert C. McIntyre, Jr. 1 , Ani Banerjee 1 ; 1 University of Colorado Health Sciences Center, Denver, CO; 2 The Children’s Hos- pital, Denver, CO; 3 Denver Health Medical Center, Denver, CO Background: The inflammatory response following an insult pro- vokes further tissue damage and the macrophage is central in this pathophysiology. Induction of heme oxygenase-1 (HO-1) attenuates post-shock organ dysfunction, although the mechanism remains un- clear. Our hypothesis was HO-1 up-regulation will modify the cyto- kine profile of LPS stimulated macrophages. Methods: HO-1 was induced in the murine macrophage cell line RAW 264.7 with 0-20% concentrations of a hemoglobin based oxygen carrier (HBOC). HO-1 expression was analyzed by Western blotting of whole cell lysates. Subsequently, macrophages were pre-treated with 20% HBOC for 4 hours, washed and then media with  10 ng/mL LPS and  5mM of the HO-1 inhibitor zinc protoporphyrin (ZnPP) was added for an additional 4 hours. Supernatants were analyzed for IL-6, IL-10, TNF-, and MCP-1 via ELISA. Experimental groups (HO-1 and ZnPP) were normalized to their own controls and data are presented as fraction change from control  SEM. Results: Incubation of cells with HBOC produced a dose dependant up-regulation of HO-1 (Fig- ure 1). HO-1 up-regulation decreased LPS induced MCP-1 to 22% (274 pg/ml vs. 1441 pg/ml), IL-6 to 57% (312 pg/ml vs. 541 pg/ml), IL-10 to 80% (803 pg/ml vs. 977 pg/ml), and TNF- to 84% (49,465 pg/mL vs. 42,179 pg/mL) of LPS stimulated controls (Figure 2). The addition of ZnPP to inhibit HO-1 partially restored MCP-1 secretion to 54% (vs. 17%, p  0.05) and IL-6 secretion to 80% (vs. 61%, p  0.05) of LPS stimulated control (Figure 3). Conclusions: HBOC up-regulates HO-1 in macrophages and this up-regulation reduces LPS induced cytokine release. Restoration of MCP-1 secretion by ZnPP further supports the key role of HO-1up-regulation. These data encourage continued investigation into the clinical potential of HBOCs for HO-1 up-regulation. 427 ASSOCIATION FOR ACADEMIC SURGERY AND SOCIETY OF UNIVERSITY SURGEONS—ABSTRACTS