In sepsis, both necrotic and apoptotic cell death can occur. Apoptotic cells induce anergy that could impair the host response, whereas necrotic cells cause immune activation that might result in enhanced antimicrobial defenses. We determined whether adoptive transfer of apoptotic or necrotic cells impacted survival in a clinically relevant sepsis model. We also evaluated the effects of adoptive transfer of apoptotic or necrotic cells on the prototypical TH1 and TH2 cytokines IFN-␥ and IL-4, respectively. C57BL6͞J mice had adoptive transfer of apoptotic (irradiated) or necrotic (freeze thaw) splenocytes. Controls received saline. Apoptotic cells greatly increased mortality, whereas necrotic splenocytes markedly improved survival, P < 0.05. The contrasting effects that apoptotic or necrotic cells exerted on survival were mirrored by opposite effects on splenocyte IFN-␥ production with greatly decreased and increased production, respectively. Importantly, either administration of anti-IFN-␥ antibodies or use of IFN-␥ knockout mice prevented the survival benefit occurring with necrotic cells. This study demonstrates that the type of cell death impacts survival in a clinically relevant model and identifies a mechanism for the immune suppression that is a hallmark of sepsis. Necrotic cells (and likely apoptotic cells) exert their effects via modulation of IFN-␥. Sepsis is the leading cause of death in many intensive-care units and currently ranks as the 12th most common cause of death in America (1). Septic patients are severely immune suppressed as typified by their loss of delayed type hypersensitivity, inability to eradicate their primary infection, and a predisposition to develop secondary nosocomial infections (2-6). A feature illustrative of the immune suppression in septic patients is their failure to respond to skin testing with antigens derived from microbes to which previous exposure occurred (positive controls) (2, 7). Animal studies indicate that the immune defect in sepsis may be critical to the pathogenesis and resultant mortality (8-10). Evidence to support this contention is also provided by a recent clinical trial using IFN-␥. Administration of this cytokine, which is a potent macrophage activator and an inducer of the TH1 response, improved survival in patients with sepsis (11).A number of defects in the immune system have been reported in sepsis. These abnormalities include a shift from a proinflammatory TH1 to an antiinflammatory TH2 lymphocyte profile, a loss in cellular MHC II expression, and a profound apoptosisinduced depletion of CD4 T and B cells (5,(11)(12)(13)(14)(15). The sepsis-induced apoptosis of lymphocytes may be particularly important not only because of the extensive lymphocyte loss but also because of a potential immunosuppressive effect of apoptotic cells on the immune system. Recent work has demonstrated that uptake of apoptotic cells by phagocytic cells stimulates immune tolerance by the release of antiinflammatory cytokines and suppression of release of proinflammatory cytokin...

Sepsis continues to be the primary cause of death among patients in surgical intensive care units. In many cases, death does not result from the initial septic event but rather from subsequent nosocomial infection with pneumonia being the most common etiology. In addition, most deaths in patients with sepsis occur after the first 72 h. By contrast, in most animal models of sepsis, most deaths occur within the first 72 h. The purpose of this study was to develop a clinically relevant "two-hit" model of sepsis that would reflect delayed mortality because of secondary nosocomial infection. The well-accepted and widely used cecal ligation and puncture (CLP) model was used as the "first hit". Pseudomonas aeruginosa or Streptococcus pneumoniae was used to induce pneumonia in mice 72 h after CLP as a "second hit." In this study, mortality in mice undergoing CLP followed by pneumonia was significantly higher than in mice receiving pneumonia or CLP alone. S. pneumoniae pneumonia after CLP resulted in a 95% mortality compared with a 20% mortality for pneumonia alone, P < 0.0001. Similarly, mortality of P. aeruginosa pneumonia after CLP (85%) was significantly higher than P. aeruginosa alone (20%), P < 0.0001. Mice undergoing CLP followed by P. aeruginosa pneumonia also had significantly higher levels of B- and T-cell apoptotic death. Finally, mice undergoing CLP followed by P. aeruginosa or S. pneumoniae pneumonia had significantly decreased concentrations of proinflammatory mediators monocyte chemoattractant protein-1 and interleukin (IL)-6 compared with mice undergoing CLP or pneumonia alone. In conclusion, a primary sublethal infection impairs the immune system thus rendering the host more susceptible to secondary infection and death. Double injury, that is, CLP followed by pneumonia, provides a useful tool in the study of sepsis, creating a prolonged period of infection as opposed to CLP alone. The extended duration of infection may lead to a better understanding of the mechanism of the immune dysregulation seen in clinical sepsis and therefore provides for evaluation of potential therapies that target specific stages of the immune response.

Cell penetrating peptides (CPPs) have been used to deliver the anti-apoptotic Bcl-xL-derived BH4 peptide to prevent injury-induced apoptosis both in vitro and in vivo. Here we demonstrate that the nuclear localization sequence (NLS) from the SV40 large T antigen has favorable properties for BH4 domain delivery to lymphocytes compared to sequences based on the HIV-1 TAT sequence. While both TAT-BH4 and NLS-BH4 protected primary human mononuclear cells from radiation-induced apoptotic cell death, TAT-BH4 caused persistent membrane damage and even cell death at the highest concentrations tested (5-10 μM) and correlated with in vivo toxicity as intravenous administration of TAT-BH4 caused rapid death. The NLS-BH4 peptide has significantly attenuated toxicity compared to TAT-BH4 and we established a dosing regimen of NLS-BH4 that conferred a significant survival advantage in a post-exposure treatment model of LD90 total body irradiation.

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