Sepsis alters the megakaryocyte-platelet transcriptional axis resulting in granzyme B-mediated lymphotoxicity.

RATIONALE: Sepsis-related mortality results in part from immunodeficiency secondary to profound lymphoid apoptosis. The biological mechanisms responsible are not understood. OBJECTIVES: Because recent evidence shows that platelets are involved in microvascular inflammation and that they accumulate in lymphoid microvasculature in sepsis, we hypothesized a direct role for platelets in sepsis-related lymphoid apoptosis. METHODS: We studied megakaryocytes and platelets from a murine-induced sepsis model, with validation in septic children, which showed induction of the cytotoxic serine protease granzyme B. MEASUREMENTS AND MAIN RESULTS: Platelets from septic mice induced marked apoptosis of healthy splenocytes ex vivo. Platelets from septic granzyme B null (-/-) mice showed no lymphotoxicity. CONCLUSIONS: Our findings establish a conceptual advance in sepsis: Septic megakaryocytes produce platelets with acutely altered mRNA profiles, and these platelets mediate lymphotoxicity via granzyme B. Given the contribution of lymphoid apoptosis to sepsis-related mortality, modulation of platelet granzyme B becomes an important new target for investigation and therapy.

NKG2A inhibits TH2 cell effector function in vitro.

BACKGROUND: We previously reported that NKG2A, a key inhibitory ligand for HLA-E, is expressed on activated TH2 but not TH1 cells. Here we measured cytokine expression in human ex vivo TH2 cells upon activation with anti-CD3/28 and challenge with an NKG2A-specific agonist. METHODS: TH2 cells were purified from healthy volunteers and activated with anti-CD3/28 in the presence and absence of NKG2A-specific agonist. IL-4 was used as a marker of TH2 effector function and measured by flow cytometry. RESULTS: Activation of TH2 cells increased NKG2A positivity from (Mean +/- SE) 7.3 +/- 2.4% to 13.7 +/- 3.8%; (p = 0.03). The presence of NKG2A agonist did not significantly alter NKG2A expression, however, the percentage of activated TH2 cells expressing intracellular IL-4 decreased from 25.5 +/- 6.8% to 9.3 +/- 4.8% (p = 0.001). CONCLUSION: We show that signalling through NKG2A suppresses TH2 effector function. This may provide a means to modulate Th1/Th2 balance in diseases where Th2 cytokines predominate.

Toward early identification of acute lung injury in the emergency department.

BACKGROUND: There are no studies evaluating the epidemiology of pediatric acute lung injury (ALI) in the emergency department (ED), where early identification and interventions are most likely to be helpful. The purpose of this study was to describe the epidemiology of the ALI precursor acute hypoxemic respiratory failure (AHRF) in the ED. METHODS: We analyzed 11,664 pediatric patient records from 16 EDs. Records were selected if oxygen saturation (SpO(2)) was recorded during the visit. Virtual partial pressure of oxygen (pO(2)) was calculated from SpO(2), thus allowing calculation of ratios of pO(2) to fraction of inspired oxygen (FiO(2)) (PFRs). Patients with a PFR < 300 were classified as having AHRF. Univariate analyses and logistic regression were used to test the association of clinical factors with the presence of AHRF and intubation. RESULTS: AHRF criteria (ie, PFR < 300) were met in 121 (2.9%) of the 4,184 patients with an oxygenation measurement. The following variables were independently associated with ALI: higher Pediatric Risk of Admission II score (adjusted odds ratio [95% confidence interval (CI)] = 1.12 [1.08-1.16]; p < .001), higher heart rate (1.02 [1.01-1.03]; p = .009), a positive chest radiograph (2.35 [1.02-5.43]; p = .045), and lower temperature (0.49 [0.36-0.68]; p < .001).The final model had an R(2) = .20. CONCLUSION: We found nonintubated AHRF to be prevalent in the ED. The low R(2) for the regression model for AHRF underscores the lack of criteria for early identification of patients with respiratory compromise. Our findings represent an important first step toward establishing the true incidence of ALI in the pediatric ED.