Elevation in pulmonary neutrophils and prolonged production of pulmonary macrophage inflammatory protein-2 after burn injury with prior alcohol exposure.

Various studies have shown that alcohol exposure before thermal injury leads to increased morbidity and mortality. Pulmonary failure is a major complication seen in these patients. This study examines the effects of prior alcohol exposure on lung pathology after burn injury. There is a marked increase in neutrophil recruitment in the lung after thermal injury, and herein we show that this appears to be significantly elevated in animals given alcohol before burn injury. Consequently, we chose to determine whether there is a difference in pulmonary production of macrophage inflammatory protein (MIP)-2, a potent neutrophil chemoattractant, in mice subjected to a 15% total body surface area scald (or sham) injury with or without prior ethanol treatment. Lung tissue was obtained at various time points after injury and homogenates were assayed for MIP-2 by enzyme-linked immunosorbent assay. At 2 h after injury, peak levels of the chemokine were produced in both burn and burn + alcohol-treated mice. This represents a 7-fold increase above baseline. In mice exposed to burn injury alone, the level of MIP-2 returned to baseline within 8 h. In contrast, mice given alcohol before burn injury continued to show elevated levels of the chemokine at 8 h, after which MIP-2 decreased. This study may provide a basis for understanding the mechanism responsible for the increased neutrophil presence in the lung after thermal injury in individuals who have consumed alcohol. Subsequently, this may lead to the enhanced neutrophil-mediated pulmonary damage observed in these patients.     

Thermal injury induces impaired function in polymorphonuclear neutrophil granulocytes and reduced control of burn wound infection

Severe thermal injury induces immunosuppression, involving all parts of the immune system, especially when large fractions of the total body surface area are affected. An animal model was established to characterize the burn‐induced immunosuppression. In our novel mouse model a 6% third‐degree burn injury was induced in mice with a hot‐air blower. The third‐degree burn was confirmed histologically. The mice were allocated into five groups: control, shave, burn, infection and burn infection group. At 48 h, a decline in the concentration of peripheral blood leucocytes was observed in the group of mice with burn wound. The reduction was ascribed to the decline in concentration of polymorphonuclear neutrophil leucocytes and monocytes. When infecting the skin with Pseudomonas aeruginosa, a dissemination of bacteria was observed only in the burn wound group. Histological characterization of the skin showed a more polymorphonuclear neutrophil granulocytes (PMNs)‐dominated inflammation in the group of mice with infected burn wound compared with the with burn wound group. In contrast, a higher degree of inflammation was observed in the burn wound group compared with the group of mice with infected burn wound. Furthermore, the oxidative burst and the phagocytic capacity of the PMNs were reduced in the group of mice with burn wound. Using this novel mouse model of thermal injury a decline of peripheral leucocytes was observed, whereas the increased local inflammatory response at the site of infection showed reduced capacity to contain and eliminate the infection.     

Experimental candidiasis after thermal injury.

The ability of Candida albicans to infect thermally injured mice was studied. Female mice were either left unburned or given a 20% total body surface area 2-s or 7-s scald burn. The wound or skin surface was then inoculated with a human burn wound isolate of C. albicans. At 4 h postburn, approximately 10(2) to 10(3) CFU/g of tissue could be recovered from the skin of burned and unburned animals. Unburned mice cleared the organisms from the skin by 72 h, whereas in 7-s-burned animals, the candida increased in numbers to approximately 10(7) CFU/g of tissue. The ability of the organisms to invade systemically after wound surface inoculation was examined in mice given either a 2-s or a 7-s scald burn. Each injury was histologically confirmed as a full-thickness (third degree) burn, with slightly deeper tissue damage observed with the 7-s burn. At each time period examined (1, 4, 7, and 10 days), there were significantly fewer organisms in the wounds of mice given the 2-s injury than in wounds of mice burned for 7 s (P less than 0.05). In 3 of 33 mice given a 7-s injury, organisms were recovered from the kidneys at the time of sacrifice, whereas no evidence of invasion into the kidneys was noted in mice given a 2-s thermal injury. This study demonstrated that thermal injury enhances the ability of C. albicans to infect mice and that the depth of burn appears to be an important factor in determining whether the organisms can invade the burn wound to cause systemic infection. This animal model should be valuable in elucidating the virulence factors of C. albicans that play a role in the pathogenesis of candidiasis after thermal injury.     

Mechanisms of lymphocyte migration in autoimmune disease

The recruitment of leukocytes to inflamed tissues plays an essential role in combating infection and promoting wound healing. However, in autoimmune diseases such as multiple sclerosis and diabetes, leukocytes enter tissues and contribute to inappropriate inflammatory responses, which cause tissue injury and dysfunction. In diseases of this type, lymphocytes play critical roles in initiating and maintaining these aberrant inflammatory responses. The aim of this review is to examine the mechanisms whereby T-lymphocytes enter tissues in autoimmune diseases and to compare these mechanisms between various organs and diseases. An overview of the mechanisms of leukocyte recruitment and the techniques used to study leukocyte trafficking is provided, focusing on the use of intravital microscopy as a tool to assess the functional microvasculature in vivo. We also discuss the series of tissue homing events which allow na?ve lymphocytes to first enter lymph nodes and undergo activation, then subsequently to home to the peripheral organ where their cognate antigen is present. Finally, we examine mechanisms of leukocyte recruitment in diseases such as multiple sclerosis, autoimmune diabetes, systemic lupus erythematosus, rheumatoid arthritis, inflammatory bowel disease and asthma.     

Linking the "two-hit" response following injury to enhanced TLR4 reactivity

Severe injury can initiate an exaggerated systemic inflammatory response and multiple organ failure (MOF) if a subsequent immune stimulus, "second hit", occurs. Using a mouse thermal injury model, we tested whether changes in innate immune cell reactivity following injury can contribute to the development of heightened inflammation and MOF. Using high-purity Escherichia coli lipopolysaccharide (LPS) to selectively stimulate Toll-like receptor 4 (TLR4), we demonstrate augmented interleukin (IL)-1beta, tumor necrosis factor alpha (TNF-alpha), and IL-6 production by 1 day but particularly, at 7 days after injury. The in vivo significance of enhanced TLR4 responsiveness was explored by challenging sham or burn mice with LPS at 1 or 7 days after injury and determining mortality along with in vivo cytokine and chemokine levels. Mortality was high (75%) in LPS-challenged burn but not sham mice at 7 days, although not at 1 day, after injury. Death was associated with leukocyte sequestration in the lungs and livers along with increased proinflammatory cytokine and chemokine levels in these organs. Blocking TNF-alpha activity prevented this mortality, suggesting that excessive TNF-alpha production contributes to this lethal response. These findings demonstrate the potential lethality of excessive TLR4 reactivity after injury and provide an explanation for the exaggerated inflammatory response to a second hit, which can occur following severe injury.     

Histopathological evaluation of the healing effects of human amniotic membrane transplantation in third-degree burn wound injuries

Skin burn injuries result in loss of its protective function as a barrier and leading to a high risk of infection. Therefore, effective treatments and healing of burn injuries are very important to prevent complications. Amniotic membrane (AM) as a biological dressing inhibits the loss of vital fluids, water, and protein. The aim of this study was to compare the healing effects of AM and silver sulfadiazine (SSD) ointment in third-degree burn injuries in experimental rat model. Fifty-four male Sprague–Dawley rats were divided randomly into three equal groups. After induction of third-degree burn, transplantation of human AM (HAM) and SSD ointment used on wound area for treatment groups. The third group was considered as control. At days 7, 14, and 21, histopathological evaluation of burn wound area was performed using light microscopy. After 21 days, burn injury in HAM group showing lack of enough wound contraction and decrease in wound area in comparison to SSD group. Also, the healing effects were demonstrated using decline of inflammatory cell infiltration and enhanced epithelium after 21 days. The total wound score was significantly higher in the HAM group than the control and SSD ointment groups, during and at the end of the experiment (P?<?0.05). On day 21, significantly lesser inflammatory cell infiltration was noticed in the control group (P?<?0.05). Our findings showed that HAM can be used successfully as a biological treatment for experimental third-degree burn injury in animal model.     

The recall response induced by genital challenge with Chlamydia muridarum protects the oviduct from pathology but not from reinfection

The significant morbidities of ectopic pregnancy and infertility observed in women after Chlamydia trachomatis genital infection result from ascension of the bacteria from the endocervix to the oviduct, where an overly aggressive inflammatory response leads to chronic scarring and Fallopian tube obstruction. A vaccine to prevent chlamydia-induced disease is urgently needed. An important question for vaccine development is whether sterilizing immunity at the level of the oviduct is essential for protection because of the possibility that a chlamydial component drives a deleterious anamnestic T cell response upon oviduct reinfection. We show that mice inoculated with attenuated plasmid-cured strains of Chlamydia muridarum are protected from oviduct pathology upon challenge with wild-type C. muridarum Nigg despite induction of a response that did not prevent reinfection of the oviduct. Interestingly, repeated abbreviated infections with Nigg also elicited recall responses that protected the oviduct from pathology despite low-level reinfection of this vulnerable tissue site. Challenged mice displayed significant decreases in tissue infiltration of inflammatory leukocytes with marked reductions in frequencies of neutrophils but significant increases in frequencies of CD4 Th1 and CD8 T cells. An anamnestic antibody response was also detected. These data indicate that exposure to a live attenuated chlamydial vaccine or repeated abbreviated genital infection with virulent chlamydiae promotes anamnestic antibody and T cell responses that protect the oviduct from pathology despite a lack of sterilizing immunity at the site.     

Neutrophil migration during endotoxemia.

Endotoxemia is marked by a global activation of inflammatory responses, which can lead to shock, multiple organ failure, and the suppression of immune and wound healing processes. Neutrophils (PMNs) play a central role in some of these responses by accumulating in tissues and releasing reactive oxygen species and proteases that injure host structures. This review focuses on altered PMN migratory responses that occur during endotoxemia and their consequences in the development of pulmonary infection. The inflammatory mediators that might be responsible for these altered responses are discussed. The oxidant potential of PMNs is increased after exposure to endotoxin both in vitro and during clinical and experimental endotoxemia. However, other functions such as chemotaxis and phagocytosis are often depressed in these same cells. Endotoxin exposure renders PMNs hyperadhesive to endothelium. The sum of these effects produces activated inflammatory cells that are incapable of leaving the vasculature. As such, the endotoxic PMN is more likely to promote tissue injury from within microvascular beds than to clear pathogens from extravascular sites. Moreover, the functional characteristics of endotoxic PMNs are similar to those observed during trauma, burn injury, sepsis, surgery, and other inflammatory conditions. Accordingly, several clinical conditions might have a common effector in the activated, yet migratorially dysfunctional, PMN. Direct effects of endotoxin on PMNs as well as effects of endogenous mediators released during endotoxemia are discussed. Understanding PMN behavior during endotoxemia may provide basic and critical insights that can be applied to a number of inflammatory scenarios.     

The Burn Wound Inflammatory Response Is Influenced by Midazolam

Burn patients requiring hospitalization are often treated for anxiety with benzodiazepines (BDZs). Benzodiazepines are reported to influence immune system function. Immune system alterations are a major cause of burn-induced mortality. We wanted to determine whether the BDZ, midazolam given daily at an anxiolytic dose, had any influence on the burn injury-induced inflammatory response in the blood and wound. Mice received a 15% total body surface area flame burn and received either midazolam 1 mg/kg i.p. or saline 0.1 ml daily. Blood and skin wounds were harvested 24 h after injection on post-burn day 2, 3, 7, or 8. Mice treated with midazolam had significantly lower serum IL-1β (p = 0.002), TNF-α (p = 0.002), IL-6 (p = 0.016), IL-10 (p = 0.009), and TGF-β (p = 0.004) than saline-treated mice, with little impact on serum chemokine levels. In the wound, TNF-α and IL-10 were the only cytokines significantly influenced by the drug, being lower (p = 0.018) and higher (p = 0.006), respectively. The chemokines in the wound influenced significantly by midazolam were MIP-1α, MIP-1β, and MIP-2 while MCP-1 and KC were not. There were more inflammatory cells at the burn wound margin in midazolam-treated mice on post-burn day 3. Although serum nitrate/nitrite was significantly increased by midazolam (p = 0.03), both eNOS and iNOS mRNA expression in the wound were similar to the saline group. We found that midazolam given daily after burn injury significantly influenced the inflammatory response. The clinical implications of these findings on wound healing and shock following burn injury, especially larger burns, deserve further investigation.     

Insights into the role of gammadelta T lymphocytes in the immunopathogenic response to thermal injury

Studies have shown that cell-mediated immunity is markedly suppressed after thermal injury. T lymphocyte dysfunction and macrophage hyperactivity have been implicated as causative factors. Previous studies have primarily examined the effects of thermal injury on alphabeta T lymphocytes; however, the role of gammadelta T lymphocytes in the immune response after thermal injury is unclear. Therefore, wild-type mice and mice lacking the TCR delta gene (TCR delta-/-) were subjected to a third-degree scald burn and cell-mediated immune responses assessed at 7 days post-injury. TCR delta-/- mice had 75% mortality after burn injury compared with 25% mortality in the wild-type group. Plasma interleukin-6 (IL-6) levels were significantly elevated at 2, 4, and 18 h post-injury, whereas no difference was observed in tumor necrosis factor alpha (TNF-alpha) and prostaglandin E2 (PGE2) plasma levels. Plasma levels of these inflammatory mediators were similar in wild-type and TCR delta-/- mice post-injury. Splenic macrophage PGE2, IL-6, TNF-alpha, and IL-10 production was significantly increased in wild-type mice at 7 days post-injury, whereas macrophages from injured TCR delta-/- mice had a significantly attenuated capacity to produce IL-6 and TNF-alpha. In contrast, the increased release of PGE2 and IL-10 by macrophages post-injury was not reduced in TCR delta-/- mice. These results implicate a dual role for gammadelta T lymphocytes in the immunopathogenic response to burn injury: (1) they contribute to survival from the insult; and (2) they mediate the induction of a pro-inflammatory macrophage phenotype at 7 days post-injury. Thus, gammadelta T lymphocytes, in part through the modulation of macrophage activity, appear to contribute to the immune dysfunction after thermal injury.     

Inflammatory reaction and infection in severe burns

Major burn injury is a lesion where the inflammatory reaction is exported to the whole body. After a short time of hemodynamic changes, this inflammation is kept by necrotic tissues, persistence of an opened wound, and by the pulmonary and gut reactions. When infection starts, it becomes difficult to distinguish its symptoms among the inflammatory signals. The main point of the care of burn patient consists in trying to control this reaction and the immuno-depression it leads to: early excision and grafts, early enteral nutrition, perfect nursing care. There is no specific medical treatment of this state. The antibiotic use must be well weighed up. Infection is often the trigger of the multiple organ dysfunction which is the way the burn patient dies but is not mandatory.     

Correlation between pseudomonas burn wound infection and granulocyte antibacterial activity.

The relationship of granulocyte bactericidal activity with three strains of pseudomonas and the virulence of these same organisms in a scald-burned rat model was investigated. Resistance to bactericidal activity was measured for each strain, using an in vitro assay and normal rat peritoneal granulocytes. Mortality was recorded for rats receiving a 30% third-degree scald burn with simultaneous pseudomonas burn wound infection. A positive correlation between mortality and resistance to bactericidal activity of granulocytes was obtained. These studies stress the importance of pseydomonas strain specificity in burn wound infection and indicate that mortality from these strains may be specifically related to their resistance to the bactericidal activity of leukocytes.     

Burn wound infections

Burns are one of the most common and devastating forms of trauma. Patients with serious thermal injury require immediate specialized care in order to minimize morbidity and mortality. Significant thermal injuries induce a state of immunosuppression that predisposes burn patients to infectious complications. A current summary of the classifications of burn wound infections, including their diagnosis, treatment, and prevention, is given. Early excision of the eschar has substantially decreased the incidence of invasive burn wound infection and secondary sepsis, but most deaths in severely burn-injured patients are still due to burn wound sepsis or complications due to inhalation injury. Burn patients are also at risk for developing sepsis secondary to pneumonia, catheter-related infections, and suppurative thrombophlebitis. The introduction of silver-impregnated devices (e.g., central lines and Foley urinary catheters) may reduce the incidence of nosocomial infections due to prolonged placement of these devices. Improved outcomes for severely burned patients have been attributed to medical advances in fluid resuscitation, nutritional support, pulmonary and burn wound care, and infection control practices.     

Impairment of granulomatous inflammatory response to Histoplasma capsulatum by inhibitors of angiotensin-converting enzyme.

Systemic infection with Histoplasma capsulatum induced a granulomatous inflammatory response in the lymphoreticular organs of C57BL/6 mice that was associated with elevated levels of angiotensin-converting enzyme (ACE) in the spleens. To determine the influence of ACE on the granulomatous response, either captopril or MK 421, two inhibitors of ACE, were administered intraperitoneally to mice 6 h after intravenous injection of H. capsulatum and then daily for 1 week. Each ACE inhibitor sharply reduced ACE activity in the spleens of infected mice. Both drugs worsened the clinical severity of infection and significantly increased the growth of H. capsulatum in livers and spleens of mice infected for 1 week. The histopathological changes in mice given captopril were more severe, with massive infiltrates of macrophages in proximity to large aggregates of yeasts. Conversely, the administration of captopril for 2 weeks during the resolving phases of infection did not slow the healing of the granulomatous lesions, nor did it provoke a relapse of infection. Captopril did not promote the growth of H. capsulatum in artificial medium. This drug was not cytotoxic to peripheral blood leukocytes or to splenic leukocytes from normal and infected mice. Administration of captopril to normal mice for 1 week did not depress the response of splenocytes of concanavalin A or to phytohemagglutinin, nor did it diminish delayed-type hypersensitivity responses in vivo. Finally, captopril did not augment the growth of H. capsulatum within macrophages. Our results suggest that ACE may participate in the regulation of the granulomatous inflammatory response to H. capsulatum and that ACE inhibition impairs the protective effects of granulomatous inflammation during acute H. capsulatum infection.     

Macrophage depletion impairs wound healing and increases left ventricular remodeling after myocardial injury in mice

Macrophages have been suggested to be beneficial for myocardial wound healing. We investigated the role of macrophages in myocardial wound healing by inhibition of macrophage infiltration after myocardial injury. We used a murine cryoinjury model to induce left ventricular damage. Infiltrating macrophages were depleted during the 1st week after cryoinjury by serial intravenous injections of clodronate-containing liposomes. After injury, the presence of macrophages, which secreted high levels of transforming growth factor-beta and vascular endothelial growth factor-A, led to rapid removal of cell debris and replacement by granulation tissue containing inflammatory cells and blood vessels, followed by myofibroblast infiltration and collagen deposition. In macrophage-depleted hearts, nonresorbed cell debris was still observed 4 weeks after injury. Secretion of transforming growth factor-beta and vascular endothelial growth factor-A as well as neovascularization, myofibroblast infiltration, and collagen deposition decreased. Moreover, macrophage depletion resulted in a high mortality rate accompanied by increased left ventricular dilatation and wall thinning. In conclusion, infiltrating macrophage depletion markedly impairs wound healing and increases remodeling and mortality after myocardial injury, identifying the macrophage as a key player in myocardial wound healing. Based on these findings, we propose that increasing macrophage numbers early after myocardial infarction could be a clinically relevant option to promote myocardial wound healing and subsequently to reduce remodeling and heart failure.     

Inflammatory responses to cryptococcosis in congenitally athymic mice

Histopathology revealed that nu/nu mice developed both acute and chronic inflammatory responses following infection with Cryptococcus neoformans. In comparison to inflammatory responses in nu/+ mice, the responses in nu/nu mice were delayed, less intense, contained predominantly more polymorphonuclear leukocytes (PMNs) than macrophages (M phi s), and did not develop into granulomas. In addition, nu/nu mice developed cryptococcal skin lesions demonstrating that C. neoformans is dermatotropic in a T-cell deficient host. Quantitative culturing of infected organs confirmed that delayed and incomplete inflammatory responses observed in nu/nu mice correlated with their enhanced susceptibility to C. neoformans.     

Rash produced by mouse cytomegalovirus

A striking rash was produced in mice 4 days after intravenous injection of large doses of murine cytomegalovirus. Routine histology showed cell infiltration, vascular damage, and hemorrhage. Immunofluourescent staining showed dermal but not epidermal infection, and this appeared to be initiated after the localization in small blood vessels of circulating virus or of virus-containing leukocytes. The rash was accompanied by a high level of complement-requiring neutralizing antibodies in the serum and extensive deposition of immune complexes in the renal glomeruli containing immunoglobulin G, immunoglobulin M, and complement. When mice were depleted of complement by cobra venom factor, when antibody responses were reduced by cyclophosphamide treatment, or when a prostaglandin inhibitor (indomethacin) was given, the rash was much less severe. The role of direct viral damage and inflammatory and immune responses in the genesis of the lesions is discussed.     

Gr-1(+)CD11b(+) cells as an accelerator of sepsis stemming from Pseudomonas aeruginosa wound infection in thermally injured mice

Using a mouse model of thermal injury, we studied why antimicrobial peptides are not produced at the burn-site tissues and how this defect contributes to the increased susceptibility to Pseudomonas aeruginosa burn-wound infection. Logarithmic growth of P. aeruginosa was demonstrated locally (at the burn site) and systemically (in circulation) in thermally injured mice exposed to 10(2) CFU/mouse of the pathogen beneath the burn wound. However, neither systemic nor local growth of the pathogen was observed in sham burn mice when they were infected intradermally with 10(6) CFU/mouse P. aeruginosa. Murine beta-defensins (MBDs) were detected in the skin homogenates of sham burn mice. However, the amounts of MBDs were reduced greatly in the same tissue homogenates from thermally injured mice. Gr-1(+)CD11b(+) cells, with an ability to suppress antimicrobial peptide production by skin keratinocytes, were isolated from tissues surrounding the burn areas, and these cells were not obtained from skin tissues of sham burn mice. After intradermal inoculation of Gr-1(+)CD11b(+) cells, which were isolated from burn-site tissues, the production of antimicrobial peptides around the cell-inoculation site of sham burn mice decreased. Also, like thermally injured mice, these mice were shown to be susceptible to P. aeruginosa intradermal infection. These results indicate that sepsis stemming from P. aeruginosa burn-wound infection is accelerated by burn-induced Gr-1(+)CD11b(+) cells with abilities to suppress antimicrobial peptide production by epidermal keratinocytes.     

Pulmonary Aspergillus fumigatus infection in rats affects gastrointestinal homeostasis

Microbiota inhabiting mucosal tissues is involved in maintenance of their immune homeostasis. Growing body of evidence indicate that dysbiosis in gut influence immune responses at distal sites including lungs. There are also reports concerning gut involvement with pulmonary injury/inflammation in settings of respiratory viral and bacterial infections. The impact of infections with other microorganisms on gut homeostasis is not explored. In this study, the rat model of sublethal pulmonary infection with Aspergillus fumigatus was used to investigate the effect of fungal respiratory infection on gut immune-mediated homeostasis. Signs of intestinal damage, intestinal and gut-draining lymphoid tissue cytokine responses and gut bacterial microbiota diversity were examined. Intestinal injury, inflammatory cell infiltration, as well as increased levels of intestinal interferon-γ (IFN-γ) and interleukin-17 (IL-17) (as opposed to unchanged levels of anti-inflammatory cytokine IL-10) during the two-week period depict intestinal inflammation in rats with pulmonary A. fumigatus infection. It could not be ascribed to the fungus as it was not detected in the intestine of infected rats. Increased production of pro-inflammatory cytokines by major gut-draining mesenteric lymph nodes point to these lymphoid organs as places of generation of cytokine-producing cells. No changes in spleen or systemic cytokine responses was observed, showing lack of the effects of pulmonary A. fumigatus infection outside mucosal immune system. Drop of intestinal bacterial microbiota diversity (disappearance of several bacterial bands) was noted early in infection with normalization starting from day seven. From day three, appearance of new bacterial bands (unique to infected individuals, not present in controls) was seen, and some of them are pathogens. Alterations in intestinal bacterial community might have affected intestinal immune tolerance contributing to inflammation. Disruption of gut homeostasis during pulmonary infection might render gastrointestinal tract more susceptible to variety of physiological and pathological stimuli. Data which showed for the first time gut involvement with pulmonary infection with A. fumigatus provide the baseline for future studies of the impact of fungal lung infections to gut homeostasis, particularly in individuals susceptible to these infections.     

Prior elevation of IL-18 promotes rapid early IFN-gamma production during staphylococcal infection

Systemic Staphylococcus aureus infection is associated with significant morbidity and mortality arising from both bacterial and host immune factors. IL-18 is a pro-inflammatory cytokine of the IL-1 superfamily that exhibits broad functional effects in innate and acquired immune responses and which has been found in high levels in several chronic inflammatory and autoimmune diseases. Over-expression of IL-18 may promote early resolution of infection or could promote a detrimental exaggerated immune response. This was explored in a model of S. aureus infection. We report increased mortality in Swiss mice that were given recombinant IL-18 prior to inoculation with S. aureus LS-1. IL-18 administration prior to infection induced preferentially enhanced IFN-gamma mRNA expression in peripheral blood leukocytes and spleen, especially splenic NK cells. This correlated with increased IFN-gamma protein detection in serum, and leukocyte and spleen cultures at subsequent discrete time points. These data suggest that increased mortality following gram-positive infection in autoimmune diseases could in part reflect the impact of high levels of pleiotropic pro-inflammatory cytokines such as IL-18 present prior to the onset of infection.