Juan B. Ochoa

Arginase I Production in the Tumor Microenvironment by Mature Myeloid Cells Inhibits T-Cell Receptor Expression and Antigen-Specific T-Cell Responses

T cells infiltrating tumors have a decreased expression of signal transduction proteins, a diminished ability to proliferate, and a decreased production of cytokines. The mechanisms causing these changes have remained unclear. We demonstrated recently that peritoneal macrophages stimulated with interleukin 4 + interleukin 13 produce arginase I, which decreases the expression of the T-cell receptor CD3ζ chain and impairs T-cell responses. Using a 3LL murine lung carcinoma model we tested whether arginase I was produced in the tumor microenvironment and could decrease CD3ζ expression and impair T-cell function. The results show that a subpopulation of mature tumor-associated myeloid cells express high levels of arginase I, whereas tumor cells and infiltrating lymphocytes do not. Arginase I expression in the tumor was seen on day 7 after tumor injection. Tumor-associated myeloid cells also expressed high levels of cationic amino acid transporter 2B, which allowed them to rapidly incorporate l-Arginine (l-Arg) and deplete extracellular l-Arg in vitro. l-Arg depletion by tumor-associated myeloid cells blocked the re-expression of CD3ζ in stimulated T cells and inhibited antigen-specific proliferation of OT-1 and OT-2 cells. The injection of the arginase inhibitor N-hydroxy-nor-l-Arg blocked growth of s.c. 3LL lung carcinoma in mice. High levels of arginase I were also found in tumor samples of patients with non-small cell carcinoma. Therefore, arginase I production by mature myeloid cells in the tumor microenvironment may be a central mechanism for tumor evasion and may represent a target for new therapies.

Nitrogen oxide levels in patients after trauma and during sepsis.

The mediators responsible for maintenance of the hyperdynamic state and the low systemic vascular resistance (SVR) observed in sepsis have not been elucidated. Nitric oxide (.N = O) is a mediator with numerous functions, including regulation of vascular tone and a role in macrophage-mediated cytostasis and microbiostasis. Thirty-nine critically ill trauma and septic patients were studied to determine the relationship between .N = O production and the hyperdynamic state. high plasma levels of NO2-/NO3- (the stable end products of .N = O) were observed in septic patients (p less than 0.02). Low SVR and high endotoxin levels were associated with high NO2-/NO3- values (p = 0.029, p = 0.002). Changes in .N = O levels may mediate the vasodilation seen in sepsis. Low NO2-/NO3- levels were observed in trauma patients (p less than 0.001) and remained low even in the presence of sepsis (p = 0.001).

Arginase I in myeloid suppressor cells is induced by COX-2 in lung carcinoma

Myeloid suppressor cells (MSCs) producing high levels of arginase I block T cell function by depleting l-arginine in cancer, chronic infections, and trauma patients. In cancer, MSCs infiltrating tumors and in circulation are an important mechanism for tumor evasion and impair the therapeutic potential of cancer immunotherapies. However, the mechanisms that induce arginase I in MSCs in cancer are unknown. Using the 3LL mouse lung carcinoma, we aimed to characterize these mechanisms. Arginase I expression was independent of T cell–produced cytokines. Instead, tumor-derived soluble factors resistant to proteases induced and maintained arginase I expression in MSCs. 3LL tumor cells constitutively express cyclooxygenase (COX)-1 and COX-2 and produce high levels of PGE2. Genetic and pharmacological inhibition of COX-2, but not COX-1, blocked arginase I induction in vitro and in vivo. Signaling through the PGE2 receptor E-prostanoid 4 expressed in MSCs induced arginase I. Furthermore, blocking arginase I expression using COX-2 inhibitors elicited a lymphocyte-mediated antitumor response. These results demonstrate a new pathway of prostaglandin-induced immune dysfunction and provide a novel mechanism that can help explain the cancer prevention effects of COX-2 inhibitors. Furthermore, an addition of arginase I represents a clinical approach to enhance the therapeutic potential of cancer immunotherapies.

Blunt splenic injury in adults: Multi-institutional study of the Eastern Association for the Surgery of Trauma

BACKGROUND Nonoperative management of blunt injury to the spleen in adults has been applied with increasing frequency. However, the criteria for nonoperative management are controversial. The purpose of this multi-institutional study was to determine which factors predict successful observation of blunt splenic injury in adults. METHODS A total of 1,488 adults (>15 years of age) with blunt splenic injury from 27 trauma centers in 1997 were studied through the Multi-institutional Trials Committee of the Eastern Association for the Surgery of Trauma. Statistical analysis was performed with analysis of variance and extended chi2 test. Data are expressed as mean +/- SD; a value of p < 0.05 was considered significant. RESULTS A total of 38.5 % of patients went directly to the operating room (group I); 61.5% of patients were admitted with planned nonoperative management. Of the patients admitted with planned observation, 10.8% failed and required laparotomy; 82.1% of patients with an Injury Severity Score (ISS) < 15 and 46.6% of patients with ISS > 15 were successfully observed. Frequency of immediate operation correlated with American Association for the Surgery of Trauma (AAST) grades of splenic injury: I (23.9%), II (22.4%), III (38.1%), IV (73.7%), and V (94.9%) (p < 0.05). Of patients initially managed nonoperatively, the failure rate increased significantly by AAST grade of splenic injury: I (4.8%), II (9.5%), III (19.6%), IV (33.3%), and V (75.0%) (p < 0.05). A total of 60.9% of the patients failed nonoperative management within 24 hours of admission; 8% failed 9 days or later after injury. Laparotomy was ultimately performed in 19.9% of patients with small hemoperitoneum, 49.4% of patients with moderate hemoperitoneum, and 72.6% of patients with large hemoperitoneum. CONCLUSION In this multicenter study, 38.5% of adults with blunt splenic injury went directly to laparotomy. Ultimately, 54.8% of patients were successfully managed nonoperatively; the failure rate of planned observation was 10.8%, with 60.9% of failures occurring in the first 24 hours. Successful nonoperative management was associated with higher blood pressure and hematocrit, and less severe injury based on ISS, Glasgow Coma Scale, grade of splenic injury, and quantity of hemoperitoneum.

l-Arginine Consumption by Macrophages Modulates the Expression of CD3ζ Chain in T Lymphocytes

l-Arginine plays a central role in the normal function of several organs including the immune system. It is metabolized in macrophages by inducible nitric oxide synthase to produce nitric oxide, important in the cytotoxic mechanisms, and by arginase I (ASE I) and arginase II (ASE II) to synthesize l-ornithine and urea, the first being the precursor for the production of polyamines needed for cell proliferation. l-Arginine availability can modulate T cell function. Human T cells stimulated and cultured in the absence of l-arginine lose the expression of the TCR ζ-chain (CD3ζ) and have an impaired proliferation and a decreased cytokine production. The aim of this work was to test whether activated macrophages could modulate extracellular levels of l-arginine and alter T cell function, and to determine which metabolic pathway was responsible for this event. The results show that macrophages stimulated with IL-4 + IL-13 up-regulate ASE I and cationic amino acid transporter 2B, causing a rapid reduction of extracellular levels of l-arginine and inducing decreased expression of CD3ζ and diminished proliferation in normal T lymphocytes. Competitive inhibitors of ASE I or the addition of excess l-arginine lead to the re-expression of CD3ζ and recovery of T cell proliferation. In contrast, inducible nitric oxide synthase or ASE II failed to significantly reduce the extracellular levels of l-arginine and modulate CD3ζ expression. These results may provide new insights into the mechanisms leading to T cell dysfunction and the down-regulation of CD3ζ in cancer and chronic infectious diseases.

An FFP: PRBC transfusion ratio >/=1:1.5 is associated with a lower risk of mortality after massive transfusion.

OBJECTIVE The detrimental effects of coagulopathy, hypothermia, and acidosis are well described as markers for mortality after traumatic hemorrhage. Recent military experience suggests that a high fresh frozen plasma (FFP):packed red blood cell (PRBC) transfusion ratio improves outcome; however, the appropriate ratio these transfusion products should be given remains to be established in a civilian trauma population. METHODS Data were obtained from a multicenter prospective cohort study evaluating clinical outcomes in blunt injured adults with hemorrhagic shock. Those patients who required >/=8 units PRBCs within the first 12 hours postinjury were analyzed (n = 415). RESULTS Patients who received transfusion products in >/=1:1.50 FFP:PRBC ratio (high F:P ratio, n = 102) versus <1:1.50 FFP:PRBC ratio (low F:P, n = 313) required significantly less blood transfusion at 24 hours (16 +/- 9 units vs. 22 +/- 17 units, p = 0.001). Crude mortality differences between the groups did not reach statistical significance (high F:P 28% vs. low F:P 35%, p = 0.202); however, there was a significant difference in early (24 hour) mortality (high F:P 3.9% vs. low F:P 12.8%, p = 0.012). Cox proportional hazard regression revealed that receiving a high F:P ratio was independently associated with 52% lower risk of mortality after adjusting for important confounders (HR 0.48, p = 0.002, 95% CI 0.3-0.8). A high F:P ratio was not associated with a higher risk of organ failure or nosocomial infection, however, was associated with almost a twofold higher risk of acute respiratory distress syndrome, after controlling for important confounders. CONCLUSIONS In patients requiring >/=8 units of blood after serious blunt injury, an FFP:PRBC transfusion ratio >/=1:1.5 was associated with a significant lower risk of mortality but a higher risk of acute respiratory distress syndrome. The mortality risk reduction was most relevant to mortality within the first 48 hours from the time of injury. These results suggest that the mortality risk associated with an FFP:PRBC ratio <1:1.5 may occur early, possibly secondary to ongoing coagulopathy and hemorrhage. This analysis provides further justification for the prospective trial investigation into the optimal FFP:PRBC ratio required in massive transfusion practice.

CD11b+/Gr-1+ Myeloid Suppressor Cells Cause T Cell Dysfunction after Traumatic Stress

T cell dysfunction that occurs after surgery or trauma is associated with a poor clinical outcome. We describe that myeloid suppressor cells expressing CD11b+/Gr-1+ markers invade the spleen after traumatic stress and suppress T cell function through the production of arginase 1. We created a consistent model of traumatic stress in C57BL/6 mice to perform this work. A significant number of CD11b+/Gr-1+ cells expressing arginase 1 accumulated in T cell zones around the germinal centers of the white pulp of the spleen within 6 h of trauma and lasted for at least 72 h. Increased arginase activity and arginase 1 expression, along with increased [3H]arginine uptake, l-arginine depletion, and l-ornithine accumulation in the culture medium, were observed exclusively in CD11b+/Gr-1+ cells after traumatic stress. Flow cytometry revealed CD11b+/Gr-1+ as a heterogeneous myeloid suppressor cell also expressing low levels of MHC class I and II, CD80, CD86, CD31, and others. When compared with controls, trauma-induced CD11b+/Gr-1+ cells significantly inhibited CD3/CD28-mediated T cell proliferation, TCR ζ-chain expression, and IL-2 production. The suppressive effects by trauma CD11b+/Gr-1+ cells were overcome with the arginase antagonist N-hydroxy-nor-l-arginine or extrasupplementation of medium with l-arginine. Poor Ag-presenting capacity of control and trauma-induced CD11b+/Gr-1+ cells was detected in allogeneic murine leukocyte reaction. This study demonstrates that CD11b+/Gr-1+ cells invade the spleen following traumatic stress and cause T cell dysfunction by an arginase-mediated mechanism, probably that of arginine depletion. Understanding the mechanism of immune suppression by these cells has important clinical implications in the treatment of immune dysfunction after trauma or surgery.

Inhibition of nitric oxide synthesis during endotoxemia promotes intrahepatic thrombosis and an oxygen radical-mediated hepatic injury.

Corynebacterium parvum‐treated mice produce large amounts of circulating nitrogen oxides and develop a severe liver injury in response to lipopolysaccharide (LPS). Concurrent administration of NG‐monomethyl‐L‐ arginine not only suppresses nitric oxide synthesis in these animals but also profoundly increases the hepatic damage following LPS. In this report, we present evidence that the increased hepatic damage from inhibition of nitric oxide synthesis is mediated in part by superoxide and hydroxyl radicals. The hepatic damage induced by suppressing nitric oxide production during endotoxemia could be reduced by treating mice with superoxide dismutase and deferoxamine, scavengers of superoxide and hydroxyl radicals, respectively. This damage could also be prevented by treating mice with the anticoagulant heparin sodium. The results suggest that nitric oxide synthesis during endotoxemia is important in preventing hepatic damage by reducing oxygen radical‐mediated hepatic injury and preventing intravascular thrombosis.

Multiple cytokines are required to induce hepatocyte nitric oxide production and inhibit total protein synthesis.

The etiology and mechanisms by which severe trauma or sepsis induce hepatic failure are unknown. Previously we showed that Kupffer cells (KC), the fixed macrophages of the liver, induce a profound decrease in hepatocyte (HC) total-protein synthesis when exposed to endotoxin. Furthermore we demonstrated that endotoxin-activated KCs induce these changes in HC protein synthesis through the induction of a novel L-arginine-dependent biochemical pathway within the HC. In this pathway, the guanido nitrogen of L-arginine is converted to the highly reactive molecule nitric oxide (NO.). To identify the KC factors that act as signals for induction of HC NO. biosynthesis, recombinant cytokines were added to HC cultures and HC nitrogen oxide production and protein synthesis levels were determined. We found that no single cytokine, but rather a specific combination of tumor necrosis factor, interleukin-1, interferon-gamma, and endotoxin, were required for maximal induction of HC nitrogen oxide production. This specific combination of cytokines induced a 248.8 +/- 26.0 mumol/L (micromolar) increase in HC nitrogen oxide production and simultaneously inhibited HC total protein synthesis by 36.1% +/- 3.1%. These data demonstrate that multiple cytokines, produced by endotoxin-activated KC, induce the production of NO. within HC, which in turn leads to the inhibition of HC total-protein synthesis.

Arginine and Immunity

For many years, dietary arginine supplementation, often combined with other substances, has been used as a mechanism to boost the immune system. Considerable controversy, however, exists as to the benefits and indications of dietary arginine due in part to a poor understanding of the role played by this amino acid in maintaining immune function. Emerging knowledge promises to clear this controversy and allow for arginines safe use. In myeloid cells, arginine is mainly metabolized either by inducible nitric oxide (NO) synthases (iNOS) or by arginase 1, enzymes that are stimulated by T helper 1 or 2 cytokines, respectively. Thus, activation of iNOS or arginase (or both) reflects the type of inflammatory response in a specific disease process. Myeloid suppressor cells (MSC) expressing arginase have been described in trauma (in both mice and humans), intra-abdominal sepsis, certain infections, and prominently, cancer. Myeloid cells expressing arginase have been shown to accumulate in patients with cancer. Arginase 1 expression is also detected in mononuclear cells after trauma or surgery. MSC efficiently deplete arginine and generate ornithine. Through arginine depletion, MSC may control NO production and regulate other arginine-dependent biological processes. Low circulating arginine has been documented in trauma and cancer, suggesting that MSC may exert a systemic effect and cause a state of arginine deficiency. Simultaneously, T lymphocytes depend on arginine for proliferation, zeta-chain peptide and T-cell receptor complex expression, and the development of memory. T-cells cocultured with MSC exhibit the molecular and functional effects associated with arginine deficiency. Not surprisingly, T-cell abnormalities, including decreased proliferation and loss of the zeta-chain, are observed in cancer and after trauma.