Experimental and clinical significance of endotoxin-dependent HLA-DR expression on monocytes

Interrogating the sepsis host immune response using cytomics

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2023. Other selected articles can be found online at https://www.biomedcentral.com/collections/annualupdate2023 . Further information about the Annual Update in Intensive Care and Emergency Medicine is available from https://link.springer.com/bookseries/8901 .

Changes in phenotypic patterns of blood monocytes after kidney transplantation and during acute rejection

Peripheral blood monocytes, which serve as precursors for tissue macrophages and dendritic cells (DC), play a key role in the immune response to kidney allograft, reparation processes and homeostasis regulation. In this prospective study, we used multicolor flow cytometry to monitor the phenotypic patterns of peripheral monocytes in subjects with uncomplicated outcomes and those with acute rejection. We found a reciprocal increase in the proportion of "classical monocytes" (CD14+CD16-) along with a decline in pro-inflammatory "intermediary" (CD14+CD16+) and "non-classical" (CD14lowCD16+) monocytes in subjects with normal outcomes. In subjects with acute rejection, we observed no reduction in "intermediary" monocytes and no increase in "classical" monocytes. Patients with uncomplicated outcomes exhibited downregulated HLA-DR in all three monocyte subpopulations. However, non-classical monocytes were unaffected in subjects with acute rejection. Expression of CD47 was downregulated after transplantation, while patients with antibody-mediated rejection and donor-specific antibodies showed higher pre-transplant values. In monocytes isolated at the time of biopsy, CD47 expression was higher in individuals with acute rejection compared to patients with normal outcomes one year post-transplant. Expression of CD209 (DC-SIGN) and the proportion of CD163+CD206+ subpopulations were upregulated during the first week after kidney transplantation. CD209 was also upregulated in samples taken on the day of biopsy confirming acute rejection. Our data demonstrate that kidney allograft transplantation is associated with phenotypic changes in peripheral blood monocytes during acute rejection.

The association between autoimmune disease and 30-day mortality among sepsis ICU patients: a cohort study

Introduction

Sepsis results from a dysregulated host response to an infection that is associated with an imbalance between pro- and anti-inflammatory cytokines. This imbalance is hypothesized to be a driver of patient mortality. Certain autoimmune diseases modulate the expression of cytokines involved in the pathophysiology of sepsis. However, the outcomes of patients with autoimmune disease who develop sepsis have not been studied in detail. The objective of this study is to determine whether patients with autoimmune diseases have different sepsis outcomes than patients without these comorbidities.

Methods

Using the Multiparameter Intelligent Monitoring in Intensive Care III database (v. 1.4) which contains retrospective clinical data for over 50,000 adult ICU stays, we compared 30-day mortality risk for sepsis patients with and without autoimmune disease. We used logistic regression models to control for known confounders, including demographics, disease severity, and immunomodulation medications. We used mediation analysis to evaluate how the chronic use of immunomodulation medications affects the relationship between autoimmune disease and 30-day mortality.

Results

Our study found a statistically significant 27.00% reduction in the 30-day mortality risk associated with autoimmune disease presence. This association was found to be the strongest (OR 0.71, 95% CI 0.54–0.93, P = 0.014) among patients with septic shock. The autoimmune disease-30-day mortality association was not mediated through the chronic use of immunomodulation medications (indirect effect OR 1.07, 95% CI 1.01–1.13, P = 0.020).

Conclusions

We demonstrated that autoimmune diseases are associated with a lower 30-day mortality risk in sepsis. Our findings suggest that autoimmune diseases affect 30-day mortality through a mechanism unrelated to the chronic use of immunomodulation medications. Since this study was conducted within a single study center, research using data from other medical centers will provide further validation.

Electronic supplementary material

The online version of this article (10.1186/s13054-019-2357-1) contains supplementary material, which is available to authorized users.

Laparoscopic Nissen fundoplication: The effects of high-concentration supplemental perioperative oxygen on the inflammatory and immune response: A randomised controlled trial

Background

A number of studies have been reported on the effects of high-concentration oxygen (HCO) on cytokine synthesis, with controversial results. We assessed the effect of administration of perioperative HCO on systemic inflammatory and immune response in patients undergoing laparoscopic Nissen fundoplication (LNF).

Materials and Methods

Patients (n = 117) were assigned randomly to an oxygen/air mixture with a fraction of inspired oxygen (FiO₂) of 30% (n = 58) or 80% (n = 59). Administration was commenced after induction of anaesthesia and maintained for 6 h after surgery. White blood cells, peripheral lymphocytes subpopulation, human leucocyte antigen-DR (HLA-DR), neutrophil elastase, interleukin (IL)-1 and IL-6 and C-reactive protein (CRP) were investigated.

Results

A significantly higher concentration of neutrophil elastase, IL-1, IL-6 and CRP was detected post-operatively in the 30% FiO₂group patients in comparison with the 80% FiO₂group (P < 0.05). A statistically significant change in HLA-DR expression was recorded post-operatively at 24 h, as a reduction of this antigen expressed on monocyte surface in patients from 30% FiO₂group; no changes were noted in 80% FiO₂group (P < 0.05).

Conclusions

This study demonstrated that perioperative HCO (80%), during LNF, can lead to a reduction in post-operative inflammatory response, and possibly, avoid post-operative immunosuppression.

Non-classical MHC I-E negatively regulates macrophage activation and Th17 cell development in NOD mice

Transgenic expression of I-E molecules prevents diabetes in NOD mice. So far, the precise role of these non-classical MHC II molecules remains elusive. Here, we showed that transgenic expression of I-E^k alpha 16 molecule in NOD mice selectively reduced Th17 cells in the thymus and pancreatic draining lymph nodes. The reduction in Th17 cells was associated with both attenuated IL-6 production and decreased activation of macrophages. Mechanistically, transgenic expression of the I-E molecule diminished expression of intracellular classical MHC II molecule and led to impaired TLR4-mediated signaling. In contrast to classical MHC II molecule, this non-classical MHC II molecule negatively regulates the inflammatory responses of macrophages. Altogether, our study reveals a novel regulatory role of I-E molecules in modulating inflammatory immune responses.

The growing spectrum of anti-inflammatory interleukins and their potential roles in the development of sepsis

Sepsis, recognized as a deadly immunological disorder, is one of the major causes of death in intensive care units globally. Traditionally, sepsis was characterized by an excessive systemic proinflammatory response to invasive microbial pathogens. However, failures of highly sophisticated trials directed toward the uncontrolled inflammatory reaction have led to an appeal by experts for reevaluation of the present approach toward sepsis. With accumulated evidence, a principal role for immunosuppression in severe sepsis has been evaluated. Different pathways of negative regulation in the pathophysiological process of sepsis have been investigated. Significant among these regulatory elements are the anti-inflammatory cytokines. In the past few years, several interleukins (ILs) have been identified and characterized, among which IL-35 and IL-37 represent newly identified ones in the spectrum of anti-inflammatory cytokines. In this study, we focus on regulatory cytokines of the IL family (including the old members: IL-4, IL-10, and IL-13, and newly discovered ones: IL-35 and IL-37) to address current knowledge regarding their structural and functional characteristics as well as their roles in the development of sepsis. Although the exact roles for these cytokines are pending further elucidation, the current advances in our understanding of mechanisms that regulate the immune responses during severe sepsis may lead to the identification of new diagnostic or treatment targets.

Innate Immune Responses in Ventilator-Associated Pneumonia

Ventilator-associated pneumonia (VAP) is a common complication of mechanical ventilation, resulting in substantial morbidity, mortality, and health care cost. Early upper airway colonization by pathogenic bacteria and microaspiration are the primary pathogenic events leading to VAP. Patients at risk for VAP have defects in structural/mechanical defenses of the respiratory tract. In addition, critical illness, including sepsis, trauma, and postoperative states, is associated with profound defects in both innate and acquired antibacterial immunity, influencing antimicrobial effector functions of both leukocytes and structural/parenchymal cells. Factors present within the lung microenvironment, including alveolar stretch, cyclical atelectasis, changes in oxygen tension, and respiratory tract microbiota, substantially impact antibacterial host responses. Mechanisms accounting for dysregulated immune homeostasis are incompletely understood, but likely involve: (1) alterations in the balance of pro- and anti-inflammatory cytokines; (2) changes in pathogen recognition receptor and G-protein coupled receptor expression and downstream signaling cascades; and (3) dysregulated cell death responses. Antibiotics and preventive strategies are the mainstay of therapy in patients with VAP. However, novel approaches are needed to reverse immunological reprogramming that occurs during critical illness and/or mechanical ventilation, and to identify patients who are most likely to benefit from immunomodulatory therapy.

Intracellular MHC class II molecules promote TLR-triggered innate immune responses by maintaining activation of the kinase Btk

The molecular mechanisms involved in the full activation of innate immunity achieved through Toll-like receptors (TLRs) remain to be fully elucidated. In addition to their classical antigen-presenting function, major histocompatibility complex (MHC) class II molecules might mediate reverse signaling. Here we report that deficiency in MHC class II attenuated the TLR-triggered production of proinflammatory cytokines and type I interferon in macrophages and dendritic cells, which protected mice from endotoxin shock. Intracellular MHC class II molecules interacted with the tyrosine kinase Btk via the costimulatory molecule CD40 and maintained Btk activation, but cell surface MHC class II molecules did not. Then, Btk interacted with the adaptor molecules MyD88 and TRIF and thereby promoted TLR signaling. Therefore, intracellular MHC class II molecules can act as adaptors, promoting full activation of TLR-triggered innate immune responses.

γ-Irradiation Enhances Apoptosis Induced by Cannabidiol, a Non-psychotropic Cannabinoid, in Cultured HL-60 Myeloblastic Leukemia Cells

Two non-psychotropic cannabinoids, cannabidiol (CBD) and cannabidiol-dimethylheptyl (CBD-DMH), induced apoptosis in a human acute myeloid leukemia (AML) HL-60 cell line. Apoptosis was determined by staining with bisBenzimide and propidium iodide. A dose dependent increase of apoptosis was noted, reaching 61 and 43% with 8 microg/ml CBD and 15 microg/ml CBD-DMH, respectively, after a 24 h treatment. Prior exposure of the cells to gamma-irradiation (800 cGy) markedly enhanced apoptosis, reaching values of 93 and 95%, respectively. Human monocytes from normal individuals were resistant to either cannabinoids or gamma-irradiation. Caspase-3 activation was observed after the cannabinoid treatment, and may represent a mechanism for the apoptosis. Our data suggest a possible new approach to treatment of AML.

The Systemic Response to Lung Infection

The host response to microbial invasion in the lung must be sufficiently vigorous to allow for microbial eradication but appropriately controlled to prevent spillover of the response into the systemic circulation. Although inflammatory responses in pneumonia are generally compartmentalized, microbial and host factors can promote disordered systemic responses to lung infection. Assessment of the magnitude of the systemic inflammatory response in pneumonia is of limited clinical value, and attempts to suppress this response have failed to improve clinical outcomes. The systemic inflammatory response that occurs in sepsis and other critical illnesses can substantially impair lung innate and acquired immunity. Mechanisms of critical illness-induced immunoparalysis have been incompletely characterized and are the focus of ongoing clinical and basic investigations.

Paradoxical Cytoskeleton and Microparticle Formation Changes in Monocytes and Polymorphonuclear Leukocytes in Severe Systemic Inflammatory Response Syndrome Patients

BACKGROUND

Circulating monocytes and polymorphonuclear leukocytes (PMNLs) are considered as central regulators controlling systemic inflammatory response after severe insults. Recently, activated monocytes and PMNLs have been reported to produce microparticles (MPs) in vitro. The objective of this study was to evaluate production of MPs and changes of cytoskeleton in monocytes from severe systemic inflammatory response syndrome (SIRS) patients, and to compare them with those in PMNLs.

METHODS

Twenty severe SIRS patients (SIRS criteria and serum C-reactive protein > 10 mg/dL) and 15 healthy volunteers were included. MP formation and F-actin content in monocytes and PMNLs were measured by flow cytometry in the presence or absence of lipopolysaccharide or formylmethionyl-leucyl-phenylalanine (FMLP). The membrane expression of human leukocyte antigen-DR and CD64 in monocytes and O2- production in PMNLs were also measured by flow cytometry.

RESULTS

In severe SIRS patients, MP formation with and without lipopolysaccharide in monocytes significantly decreased in comparison with those in normal controls (p < 0.05), whereas those with and without FMLP in PMNLs increased (p < 0.05). F-actin content with and without FMLP in monocytes also significantly decreased in patients (p < 0.05), whereas those in PMNLs increased as compared with normal controls (p < 0.05). The expression of human leukocyte antigen-DR in monocytes significantly decreased in patients (p < 0.05), which indicated monocyte modulation. The O2- production in PMNLs increased in patients (p < 0.05), which showed PMNL activation.

CONCLUSION

The changes of MP formation and cytoskeleton in circulating monocytes and PMNLs were paradoxically different in severe SIRS patients.

Sepsis-induced immunosuppression: from bad to worse

The sepsis syndrome is characterized by the acute release of a variety of inflammatory mediators, which often result in detrimental effects to the host. The release of these mediators is regulated and counterbalanced by the coordinated expression of antiinflammatory molecules. It is the balance between the expression of pro- and antiinflammatory mediators that often determines the magnitude of early tissue injury and subsequent risk of infectious complications. As our understanding of the pathophysiology of sepsis continues to evolve, we have gained a greater appreciation for the effects that sepsis and similar states of overwhelming stress have on host antimicrobial immunity. A number of functional defects in leukocytes isolated from sepsis patients have been characterized. These defects include diminished expression of important cell surface antigens, dysregulated cytokine production, alterations in antigen-presenting ability, and accelerated apoptosis. Impaired leukocyte function has important clinical ramifications, as high mortality rates have been observed in patients displaying evidence of sepsis-induced immune deactivation. In this article, we review the current literature supporting evidence of dysregulation of host immunity occurring during sepsis syndrome, characterize the underlying pathophysiology, and describe novel therapeutic interventions directed at augmenting host immunity during sepsis.

Antibiotic induced endotoxin release and clinical sepsis: a review

Sepsis and peritonitis have not lost much of their danger for patients. The mortality rate in peritonitis has only marginally decreased during the last 30 years despite aggressive surgical and sophisticated intensive care treatment. In intra-abdominal infection and peritonitis source control remains the mainstay of treatment, although general principles and denominators of successful source control need to be established. Endotoxin has been recognized as a major player in the pathogenesis of sepsis and its significance in clinical disease has been investigated in clinical studies for more than 20 years. Since the Sixties there is a growing interest in the effect of antibiotics and other compounds on the release of endotoxin. The effect of antibiotics on the release of endotoxin and inflammatory parameters, e.g., cytokines, remains to be clarified despite a growing body of in-vitro studies, animal studies and a few clinical studies. The purpose of this review is to evaluate the evidence of endotoxin release in clinical studies and the effect that antibiotic treatment may have in-vitro, in-vivo and in clinical studies on endotoxin and cytokine release. In-vitro antibiotic-induced endotoxin release may depend on antibiotic class, presence of serum, type of organism, site of antibiotic action and Gram-stain. Endotoxin release may be different in late or early lysis, proportional to the number of killed pathogens. Morphology of bacteria may have an impact on endotoxin release and phagocytosis. Antibiotic-treated animals may show higher endotoxin levels with a higher survival rate than untreated animals. Plasma endotoxin may increase despite decreasing bacteremia. There may be a similar killing rate by different antibiotics but a difference in endotoxin release. Intestinal endotoxin does not necessarily correlate to the level of gram-negative bacteria. However, the alteration of the gut content by pretreatment may be associated with reduced endotoxemia and increased survival. Antibiotic-induced endotoxin release may be different depending on the type of infection, the location of infection, the virulence of strains, Gram-stain, mode of application and dosage of antibiotic. Different antibiotics may induce the release of different forms of endotoxin which may be lethal for sensitized animals. The combination of antibiotics with inhibitors of endotoxin or the pro-inflammatory response may be responsible for increased survival by decrease of endotoxin release. The clinical significance of antibiotic-induced endotoxin release is documented only in a few clinical disorders, e.g., meningitis, urosepsis. The difference in endotoxin release by PBP 2-specific antibiotics, e.g., imipenem, and PBP 3-specific antibiotics, e.g., ceftazidime, may not be visible in each study. Patients with increased multi-organ failure (MOF) scores may profit from treatment with antibiotics known to decrease endotoxin. In conclusion, the clinical significance of antibiotic-induced endotoxin release remains to be clarified. Type of pathogen and its virulence may be more important than recently suggested. gram-positive pathogens were just recently recognized as an important factor for the development of the host response. In case of fever of unknown origin in intensive care patients either failure of treatment, e.g., failure of source control in intra-abdominal infection, or a side effect of antibiotic treatment, e.g., endotoxin release, should be considered as a cause of the fever.

IL-10 Is a Major Mediator of Sepsis-Induced Impairment in Lung Antibacterial Host Defense

To explore the mechanism of immunosuppression associated with sepsis, we developed a murine model of sepsis-induced Pseudomonas aeruginosa pneumonia. CD-1 mice underwent either cecal ligation and 26-gauge needle puncture (CLP) or sham surgery, followed by the intratracheal (i.t.) administration of P. aeruginosa or saline. Survival in mice undergoing CLP followed 24 h later by the i.t. administration of saline or P. aeruginosa was 58% and 10%, respectively, whereas 95% of animals undergoing sham surgery followed by P. aeruginosa administration survived. Increased mortality in the CLP/P. aeruginosa group was attributable to markedly impaired lung bacterial clearance and the early development of P. aeruginosa bacteremia. The i.t. administration of bacteria to CLP-, but not sham-, operated mice resulted in an impressive intrapulmonary accumulation of neutrophils. Furthermore, P. aeruginosa challenge in septic mice resulted in a relative shift toward enhanced lung IL-10 production concomitant with a trend toward decreased IL-12. The i.p., but not i.t., administration of IL-10 Abs given just before P. aeruginosa challenge in septic mice significantly improved both survival and clearance of bacteria from the lungs of septic animals administered P. aeruginosa. Finally, alveolar macrophages isolated from animals undergoing CLP displayed a marked impairment in the ability to ingest and kill P. aeruginosa ex vivo, and this defect was partially reversed by the in vivo neutralization of IL-10. Collectively, these observations indicate that the septic response substantially impairs lung innate immunity to P. aeruginosa, and this effect is mediated primarily by endogenously produced IL-10.

Functional analysis of monocyte subsets in surgical sepsis

BACKGROUND

Sepsis still remains a major cause of death after surgery. Impaired monocyte (Mphi) function and disruption of monocyte (Mphi/T-cell interaction were shown to be crucial for the development of septic complications in these patients. It was the objective of the study to assess more insights in Mphi behavior in surgical sepsis by means of analysis of Fc receptor- and human leukocyte antigen DR (HLA-DR) expression in Mphi subsets, and to evaluate the kinetics of these changes.

METHODS

In a prospective study, 20 septic patients and 10 healthy control subjects were included. Peripheral Mphi were isolated on consecutive days after onset of sepsis, and FcR positive (FcR+) and negative (FcR-) subsets were separated by rosetting with antibody-coated human erythrocytes. Cell surface receptor expression and in vitro cytokine production were used to determine the clinical importance of these subsets.

RESULTS

A significant monocytosis (3.5-fold; p < 0.01) and suppression of HLA-DR receptor expression (35%, p < 0.01) which correlate with sepsis severity and outcome could be demonstrated. There was a significant increase of FcR+ subsets in sepsis compared with control subjects (60% vs. 24%; p < 0.05). In vitro stimulation of Mphi subsets and peripheral blood mononuclear cells revealed suppressed interferon-gamma synthesis (p < 0.05 up to 0.01) from day 1 to day 5, elevated neopterin release (p < 0.05) on day 14 and increased synthesis rates of proinflammatory cytokines (e.g., interleukin-1beta); p < 0.05) predominantly in FcR+ subsets.

CONCLUSIONS

Sepsis results in a significant monocytosis and suppression of HLA-DR receptor expression, which are correlating with sepsis severity and outcome. A significant shift toward FcR+ Mphi subsets can be found. This subpopulation resembles the previously described "angry macrophage" that is characterized by high proinflammatory cytokine synthesis and suppressed antigen presentation and that contributes to a disruption of adequate Mphi/T-cell interaction, rendering the host anergic toward opportunistic infections. The extend of HLA-DR suppression and the shift toward FcR+ Mphi might characterize a high risk patient subpopulation, which could benefit from immunomodulatory strategies.

Monocyte response to bacterial toxins, expression of cell surface receptors, and release of anti-inflammatory cytokines during sepsis

Exposure to endotoxin produces a state of macrophage hyporesponsiveness on subsequent stimulation. Monocytes in patients with septic shock demonstrate a similar hyporesponsiveness to endotoxin. The purpose of this study was to examine whether this state of hyporesponsiveness extends to other inflammatory stimuli and the relationship of this state to cell surface receptor expression and the release of anti-inflammatory cytokines. Twelve normal volunteers, 10 patients with severe sepsis, and 9 patients with septic shock were included in the study. Monocytes from each subject were isolated and stimulated with lipopolysaccharide (LPS), staphylococcal enterotoxin B (SEB), and phorbol myristate acetate (PMA). Tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) were measured in the supernatants by enzyme-linked immunosorbent assay (ELISA). Serum levels of transforming growth factor-beta1 (TGF-beta1), prostaglandin E2 (PGE2), and interleukin-10 (IL-10) were also measured by ELISA. The expression of monocyte CD14 and HLA-DR in whole blood were measured by flow cytometry. Patients with septic shock demonstrated significantly decreased TNF-alpha and IL-1beta release as compared with normal subjects in response to LPS. In response to SEB, patients with sepsis and patient with septic shock demonstrated significantly decreased release of TNF-alpha and IL-1beta. Significant decreases in TNF-alpha release were found in the patients with septic shock after PMA stimulation. There were no significant differences in the monocyte response to the different stimuli between patients with gram-positive sepsis and gram-negative sepsis. HLA-DR expression was significantly decreased in patients with septic shock (58 +/- 9 fluorescence units (flU)) as compared with normal subjects (102 +/- 14 flU) (p < 0.05). No differences in CD14 expression were observed. IL-10 levels were significantly increased in patients with sepsis (16 +/- 4 pg/ml) and in patients with septic shock (42 +/- 15 pg/ml) and were detectable in 1 normal subject. TGF-beta1 levels were decreased in patients with septic shock (25 +/- 6 pg/ml) as compared with those in normal subjects (37 +/- 2 pg/ml)(p < 0.05). PGE2 levels were significantly increased in patients with septic shock and patients with sepsis. These data are consistent with a more generalized monocyte hyporesponsiveness to bacterial toxins that may be related to altered cell surface receptor expression and the release of anti-inflammatory cytokines.

Temporal analysis of human leucocyte surface antigen expression and neutrophil respiratory burst activity after thermal injury

Sepsis, the major cause of morbidity and mortality after burn injury, is related to multiple immune derangements. Using monoclonal antibodies and two-colour flow cytometry to identify surface antigens, peripheral blood mononuclear cell (PBMC) populations were analysed and correlated with lymphocyte proliferation assays for 21 days postinjury. In addition, in vitro expression of activation antigens by mitogen-stimulated PBMCs was analysed during the time period. Twenty-nine burn patients were studied, with burn injuries ranging from 19 to 97 per cent TBSA; PBMCs from human volunteers were used for control cells. Patients received aggressive enteral nutritional support starting day 1 postburn and underwent early excision and grafting of wounds; no patients developed sepsis during the study period. The most consistent changes in PBMCs after thermal injury were decreased percentages of total T cells (CD3+), T helper/inducer cells (CD4+), and T suppressor/cytotoxic cells (CD8+); the percentages of natural killer (CD16+) cells were not altered. Expression of surface 'activation' antigens on CD4+ and CD8+ cells (HLA-DR, interleukin-2 receptor and transferrin receptor) after mitogen stimulation was significantly depressed as early as 1 day postburn. An early monocytosis was seen on day 1 postburn, but decreases were found on days 4 and 7. Monocyte expression of HLA-DR antigen was suppressed throughout the study. Lymphocyte proliferation after mitogen stimulation and the responses of lymphocytes in mixed lymphocyte culture were suppressed postburn. Neutrophil respiratory burst responses were supranormal on days 1 and 7 postburn, but the differences were not statistically significant.(ABSTRACT TRUNCATED AT 250 WORDS)

The human leukocyte antigens and their relationship to infection

Human leukocyte antigen DR (HLA-DR) expression on peripheral blood monocytes has been found to correlate highly with infection in many clinical scenarios. This is particularly true for the trauma patient, where changes in HLA-DR expression predate and therefore often predict development of infection. Expression of this antigen is limited to immunocompetent cells, such as B lymphocytes, macrophages, and activated T cells. The HLA-DR heterodimer is required for major histocompatibility complex restricted antigen presentation, a key step in the development of a specific immune response. The degree of monocyte HLA-DR expression may reflect the ability eventually to present antigen, since close correlation has been found between the two. There was remarkable reproducibility of monocyte HLA-DR expression among > 100 asymptomatic volunteers without regard to age, gender, race, and sampling time. Immunosuppressive medication had no effect. Incubation of monocytes from severely infected patients with endotoxin distinguished survivors from those who died by enhanced HLA-DR expression in the survivors. Of several agents that enhance HLA-DR expression, interferon-gamma has received the most attention in experimental models as well as humans. Although promising in selected patients, further clinical trials will be needed to define its specific role. Identification of the patient at high risk for infection, particularly following trauma, will be crucial for the efficient evaluation of future therapeutic interventions. Monocyte HLA-DR expression is the first simple assessment of the host immune response to play an important role in this endeavor.

A randomized prospective clinical trial to determine the efficacy of interferon-gamma in severely injured patients

Many aspects of the normal immune response are depressed after severe injury. Reduced monocyte human leukocyte antigen-DR (HLA-DR) levels have closely correlated with the development of major infection. After a pilot study with recombinant interferon-gamma (rIFN-gamma) showed restoration of depressed HLA-DR levels after major injury, a multicenter, prospective, randomized, double-blind trial was conducted. Two hundred thirteen trauma patients who were at high risk of infection received either placebo or rIFN-gamma (100 micrograms) subcutaneously each day for 10 days after admission. One hundred ninety-three patients were evaluable with respect to primary end points. Patients treated with rIFN-gamma were older (p = 0.10) and had more severe modes of injury (p = 0.02). By the third day, both monocyte HLA-DR antigen expression and outcome predictive score were significantly better in the rIFN-gamma-treated group than in the placebo group (p = 0.0001 and p = 0.0006, respectively). Nine deaths occurred in patients treated with rIFN-gamma compared with 12 deaths in the placebo group (p = 0.46). Major infections requiring surgical drainage or debridement occurred in 17 patients treated with rIFN-gamma compared with 22 treated with placebo. No difference between treatment arms was noted in overall major or minor infection rates, but there were fewer severe infections that required reoperation or computer tomographic-guided drainage in patients receiving IFN-gamma. While these results suggest that rIFN-gamma may be useful in some aspects of infection in the patient with severe trauma, a larger trial with longer treatment will be needed to prove the comprehensive value of rIFN-gamma.

HLA-DR antigen expression on peripheral blood monocytes correlates with surgical infection

Monocyte human leukocyte antigen-DR (HLA-DR) expression has correlated closely with clinical outcome in severely injured patients at high risk for infection. Monocytes from 77 asymptomatic volunteers expressed HLA-DR antigen with minimal variability in respect to age, gender, race, time of day or year, or serum alcohol level. Patients who developed infection after elective laparotomy had a significantly lower mean percentage of monocytes expressing HLA-DR antigen and a lower mean fluorescent intensity than uninfected patients (p less than 0.05). Severely infected nonsurgical patients had significantly lower values than normal volunteers (p less than 0.01), and the mean fluorescent intensity of those who died from infection was significantly lower than that of those who survived (p less than 0.05). Patients on immunosuppressive regimens after renal transplantation had levels of HLA-DR expression similar to those of the volunteers. Monocyte HLA-DR expression was found to be a reliable marker of clinical infection and showed remarkable reproducibility within the normal uninfected study population.

Effect of extracorporeal membrane oxygenation on leukocyte function in neonates

The impact of extracorporeal membrane oxygenation (ECMO) on neonatal leukocyte content and function was examined in six patients. Patients were treated with ECMO for a mean of 134 h (range 44-246 h). Absolute neutrophil counts decreased from 14679 +/- 2291/mm3 to 7791 +/- 1672/mm3 after 2 h of ECMO. However, neutrophil phagocytosis and oxidative burst remained unchanged during the first 48 h of bypass. Monocyte counts also decreased during bypass, and at times were undetectable in 50% of patients. Monocyte HLA-DR content was decreased compared to normal cord blood prior to initiation of ECMO, and remained low throughout ECMO. However, the content increased significantly after termination of bypass. Plasma C3a levels increased transiently, paralleled by an increase in neutrophil CR3 expression. While moribund infants had some impairment of host defenses prior to ECMO, there was no further impact of ECMO per se on the parameters measured, other than transient complement activation and decreased monocyte counts.