Characterization and Activation of Fas Ligand-Producing Mouse B Cells and Their Killer Exosomes

B lymphocytes make several contributions to immune regulation including production of antibodies with regulatory properties, release of immune suppressive cytokines, and expression of death-inducing ligands. A role for Fas ligand (FasL)-expressing "killer" B cells in regulating T helper (T_H) cell survival and chronic inflammation has been demonstrated in animal models of schistosome worm and other infections, asthma, autoimmune arthritis, and type 1 diabetes. FasL⁺ B cells were also capable of inducing immune tolerance in a male-to-female transplantation model. Interestingly, populations of B cells found in the spleen and lungs of naïve mice constitutively expresses FasL and have potent killer function against T_H cells that is antigen-specific and FasL-dependent. Epstein-Barr virus-transformed human B cells constitutively express FasL and package it into exosomes that co-express MHC Class II molecules and have killer function against antigen-specific T_H cells. FasL⁺ exosomes with markers of B-cell lineage are abundant in the spleen of naïve mice. Killer B cells therefore represent a novel target for immune modulation in many disease settings. Our laboratory has published methods of characterizing FasL⁺ B cells and inducing their proliferation in vitro. This updated chapter will describe methods of identifying and expanding killer B cells from mice, detecting FasL expression in B cells, extracting FasL⁺ exosomes from spleen and culture supernatants, and performing functional killing assays against antigen-specific T_H cells.

Characterization and activity of Fas ligand producing CD5⁺ B cells

B lymphocytes make several contributions to immune regulation including production of antibodies with regulatory properties, release of immune suppressive cytokines, and expression of death-inducing ligands. A role for Fas ligand (FasL)-expressing "killer" B cells in regulating T helper cell survival and chronic inflammation has been demonstrated in animal models of schistosome worm infection, asthma, and autoimmune arthritis. Interestingly, a population of CD5(+) B cells found in the spleen and lungs of naïve mice constitutively expresses FasL and has potent killer function against T helper cells that is antigen-specific and FasL-dependent. Killer B cells therefore represent a novel target for immune modulation in many disease settings. Our laboratory has recently published methods of characterizing FasL(+) B cells and inducing their proliferation in vitro. This chapter will describe detailed methods of identifying and expanding killer B cells from mice, detecting FasL expression in B cells, and performing functional killing assays against antigen-specific TH cells.

Apoptosis of blood mononuclear cells in alcoholic liver cirrhosis. The influence of in vitro ethanol treatment and zinc supplementation

Ethanol consumption induces apoptosis in a variety of tissues, among others in liver and lymphoid tissue. Zinc has been shown to influence apoptosis of blood mononuclear cells by inhibiting the mitochondrial pathway of cell death. The aim of this study was to examine the influence of zinc on spontaneous and in vitro alcohol-induced apoptosis of peripheral blood mononuclear cells (PBMCs) of patients with alcoholic cirrhosis. PBMCs were isolated from the blood of 26 patients with cirrhosis and 20 healthy controls. PBMCs and among them CD4+ T helper cells of cirrhotic patients exhibited accelerated spontaneous (without treatment) apoptosis in vitro. When apoptosis was induced in vitro by treating cells with 80 mM ethanol, CD8+ T lymphocytes of a healthy control were more sensitive to ethanol treatment than those of cirrhotic patients. Thirty micromolar zinc supplementation inhibited both spontaneous and ethanol-induced apoptosis of immune cells derived from the blood of the healthy control and cirrhotic patients. In sera of patients with cirrhosis, an elevated level of IL-12, but also sFas (CD95) and sFas ligand (sFasL) was detected. Moreover, in vitro, PBMCs of cirrhotic patients spontaneously released more sFas and sFasL than control PBMCs. Ethanol treatment significantly increased sFas, but decreased sFasL release from PBMCs of cirrhotic patients, while it only slightly affected control cells. As zinc supplementation did not significantly influence sFas or sFasL release, it seems likely that it is rather the mitochondrial pathway of ethanol-related immune cell death that may be inhibited by zinc supplementation.

Vγ9Vδ2 T cells use a combination of mechanisms to limit the spread of the pathogenic bacteria Brucella

Human Vgamma9Vdelta2 T cells play a crucial role in early immune response to intracellular pathogens. In brucellosis infection, this population of cells is drastically increased in the peripheral blood of patients during the acute phase of infection. In vitro, Vgamma9Vdelta2 T cells exhibit strong cytolytic activity against Brucella-infected cells and are able to impair intracellular growth of Brucella suis in autologous macrophages. In this study, we have investigated the relative importance of contact-dependent mechanisms versus soluble factors in the intracellular growth and viability of B. suis. We show that Vgamma9Vdelta2 T cells use contact-dependent mechanisms, such as the release of lytic granules and Fas-mediated signals, to decrease intracellular B. suis through lysis of infected macrophages, but these mechanisms have little impact on Brucella survival. Moreover, we demonstrate that soluble factors secreted by Vgamma9Vdelta2 T cells can directly affect B. suis survival through their potent bactericidal effects. From these results, we conclude that Vgamma9Vdelta2 T cells are able to use a combination of mechanisms that reduce the total numbers of B. suis and thus, may benefit the host by limiting the spread of this intracellular pathogen.

Regulation of Fas (APO-1, CD95) and Fas ligand expression in leukocytes during systemic inflammation in humans

A potential role of Fas/FasL in sepsis is suggested by recent clinical studies showing that Fas and FasL could serve as markers for severity of sepsis. We sought to determine the effect of endotoxin infusion on expression of Fas and FasL. Healthy volunteers (n = 30) received 2 ng/kg endotoxin i.v. Endotoxin infusion decreased Fas expression on neutrophils and monocytes by 15-20% at 2-4 h in vivo and also in vitro. A rebound increase in Fas (30%) was seen on neutrophils at 24 h, and soluble FasL levels increased by 100% at 24 h. Fas mRNA levels increased 6-fold 4-6 h after endotoxin infusion as measured by real-time polymerase chain reaction. In contrast, FasL-mRNA levels in circulating leukocytes decreased by >80% 2h after lipopolysaccharide infusion. In summary, low-grade endotoxemia induces early down-modulation of Fas on leukocytes, followed by a several-fold increase in Fas-mRNA expression leading to later Fas surface upregulation on neutrophils. The upregulation of Fas expression, Fas mRNA, and later in FasL and sFas levels in endotoxemia replicates the increased fas levels found in septic patients.

Fas and Fas ligand expression in maternal blood and in umbilical cord blood in preeclampsia

The Fas-Fas ligand (FasL) pathway of apoptosis is abnormally activated in diseases associated with impaired immune tolerance or chronic inflammation. Pregnancy-related hypertension is a spectrum of disease that commonly causes significant morbidity in women and in their newborn infants, is associated with generalized inflammation, and may be causally related to impaired maternal-fetal tolerance. Our recent observation of enhanced trophoblast expression of FasL in one form of pregnancy-related hypertension led us to hypothesize that this group of disorders might be associated with abnormal activation of the Fas-FasL pathway. To test this hypothesis, we prospectively quantified soluble and leukocyte-associated Fas receptor and FasL in the maternal and umbilical cord blood (CB) sera of 20 gestations complicated by preeclampsia and of 18 normal control gestations, using ELISA and flow cytometric analyses. We determined higher soluble FasL levels in paired maternal and CB sera of hypertensive gestations compared with control gestations (p < 0.01); in contrast, soluble Fas levels were similar between groups. Surface expression of FasL was lower on maternal (p < 0.01) and CB (p < 0.05) neutrophils from affected gestations, whereas surface Fas expression was lower on maternal (p < 0.02), but not CB, neutrophils and lymphocytes. We conclude that expression of Fas and FasL in sera and on leukocytes is altered in gestations complicated by preeclampsia, and speculate that activation of the Fas-FasL pathway mediates associated pathologic processes in affected women and in their neonates.

Expression of co-stimulatory and adhesion molecules and chemokine or apoptosis receptors on acute myeloid leukaemia: high CD40 and CD11a expression correlates with poor prognosis

The expression of adhesion and co-stimulatory molecules, and chemokine and death receptors such as tumour necrosis factor (TNF) and FAS on acute myeloid leukaemia (AML) may influence the biology of the disease and response to chemotherapy and immunotherapy. In this study, we analysed the expression of these molecules in 99 AML patients using monoclonal antibodies and flow cytometry, and correlated the expression with French-American-British (FAB) classification and survival. The following molecules were studied: the co-stimulatory molecules CD80, CD86 and CD40; the adhesion molecules CD11a-c, CD31, CD43, CD50, CD54, CD102, CD58 and CD62L; the chemokine receptor CXCR4; and the death receptors TNFR1 and TNFR2 and FAS. The expression of all molecules was significantly higher in the M4/M5 FAB subgroups except for CD80, CD43, CD54 and CD62L. The AML M3 subgroup had a significant lower expression of CD11a (P = 0.02) and CD11c (P = 0.03). Five-year survival was significantly shorter in cases of high CD40 expression [> 20% positive cells, relative risk (RR) 2.56, P = 0.02] or high CD11a expression (> 80% positive cells, RR 2.6, P = 0.03). This effect was most prominently present in the AML M4/M5 FAB subgroups. We conclude that the expression levels of adhesion and co-stimulatory molecules, CXCR4 and apoptosis-receptors are predominantly FAB subtype-related with high CD40 and CD11a expression as poor prognostic factors.

Human lymphocyte apoptosis after exposure to influenza A virus

Infection of humans with influenza A virus (IAV) results in a severe transient leukopenia. The goal of these studies was to analyze possible mechanisms behind this IAV-induced leukopenia with emphasis on the potential induction of apoptosis of lymphocytes by the virus. Analysis of lymphocyte subpopulations after exposure to IAV showed that a portion of CD3(+), CD4(+), CD8(+), and CD19(+) lymphocytes became apoptotic (terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling positive). The percentage of cells that are infected was shown to be less than the percentage of apoptotic cells, suggesting that direct effects of cell infection by the virus cannot account fully for the high level of cell death. Removal of monocytes-macrophages after IAV exposure reduced the percent of lymphocytes that were apoptotic. Treatment of virus-exposed cultures with anti-tumor necrosis factor alpha did not reduce the percentage of lymphocytes that were apoptotic. In virus-exposed cultures treated with anti-FasL antibody, recombinant soluble human Fas, Ac-DEVD-CHO (caspase-3 inhibitor), or Z-VAD-FMK (general caspase inhibitor), apoptosis and production of the active form of caspase-3 was reduced. The apoptotic cells were Fas-high-density cells while the nonapoptotic cells expressed a low density of Fas. The present studies showed that Fas-FasL signaling plays a major role in the induction of apoptosis in lymphocytes after exposure to IAV. Since the host response to influenza virus commonly results in recovery from the infection, with residual disease uncommon, lymphocyte apoptosis likely represents a part of an overall beneficial immune response but could be a possible mechanism of disease pathogenesis.

Identification of Fas-L-expressing apoptotic T lymphocytes in normal human peripheral blood : in vivo suicide

Fas-L molecules expressed by in vitro stimulated T cells may be critically involved in suicidal activation-induced cell death (AICD) of such cells through engagement of their Fas receptors. A similar suicide of T cells was postulated to occur even in vivo, to eliminate dangerous activated lymphocytes; however, the demonstration of suicidal AICD of T cells in healthy humans in vivo is still lacking. We therefore investigated the possible occurrence of Fas-L-linked suicidal apoptosis of T cells in normal human peripheral blood. For this purpose, we took advantage of immunoelectron microscopy, which allows simultaneous visualization of the morphological apoptotic cellular changes together with surface expression of Fas-L molecules. Very few T lymphocytes were observed showing the ultrastructural features of apoptotic lymphocytes; these occasional apoptotic T cells, together with the majority of the normal T cell population, expressed the Fas molecule on the plasma membrane, as expected. Interestingly, the apoptotic cells were also Fas-L-positive, whereas normal T cells were Fas-L-negative. Such Fas-L-associated T cell suicide operating in vivo in healthy individuals is presumably able to suppress immune responses and prevent autoreactivity, thus maintaining the homeostasis of human blood.

Soluble Fas and soluble Fas-ligand in children with Escherichia coli O157:H7-associated hemolytic uremic syndrome

We measured soluble Fas-ligand (sFas-L) and soluble Fas (sFas) levels by sandwich enzyme-linked immunosorbeny assay and compared them among (1) healthy controls (n = 11), (2) children with hemorrhagic colitis (HC) caused by a non-verotoxin-producing pathogen (n = 23), (3) patients with uncomplicated Escherichia coli O157:H7 HC (n = 14), and (4) children with O157:H7-associated hemolytic uremic syndrome (HUS) (n = 24). Children with uncomplicated E coli O157:H7 HC and HUS were matched for duration of enteric prodrome before blood sample collection. We also compared sFas-L and sFas levels among patients with HUS according to severity of renal dysfunction; abnormally increased sFas-L levels were noted in only 4% of the children (n = 3). Abnormally high concentrations of sFas were noted in 9% of the children with HC caused by a non-verotoxin-producing pathogen, 29% of the patients with uncomplicated E coli O157:H7 HC, and 69% of the children with O157:H7-associated HUS. Compared with healthy controls, patients with HUS had twofold greater concentrations of sFas (P: < 0.0001). Levels of sFas were not statistically different between 14 patients with uncomplicated O157:H7 HC and 14 children with HUS (8.2 +/- 4.7 versus 11.0 +/- 4.6 U/mL, respectively; P: < 0.07) when matched for time after onset of enteritis (7.0 +/- 3.7 versus 7.3 +/- 3.8 days, respectively). Greater concentrations of sFas were noted in patients with HUS who developed oligoanuria (n = 10; P: < 0.007), required peritoneal dialysis (n = 10; P: < 0.007), or had a decreased glomerular filtration rate (n = 5; P: < 0.002) 1 year later. Our data show that plasma concentrations of sFas but not sFas-L are abnormally increased in children with O157:H7 infections. Levels of sFas are associated with severity of renal dysfunction during HUS. Further studies are needed to clearly determine the role and origin of circulating sFas among children with infections caused by E coli O157:H7.

Serum soluble Fas (CD95) and Fas ligand profiles in chronic kidney failure

Apoptosis, or programmed cell death, is an active form of cell death that is initiated by a number of stimuli and is intricately regulated. Apoptosis in both excessive and reduced amounts has pathophysiologic implications. Accelerated programmed cell death has been observed in leukocytes among patients with chronic renal failure (CRF). This has been ascribed in part to the retention of uremic toxins. The Fas/Fas ligand (FasL) system is a key regulatory apoptotic pathway. Membrane-bound Fas is a cell-surface receptor that transduces apoptosis after interaction with membrane-bound or soluble FasL (sFasL). By contrast, soluble Fas (sFas) binds sFasL and inhibits its activity. In an attempt to examine the balance between these soluble factors in uremia, we measured soluble sFas and sFasL levels in the serum of healthy control subjects and patients with various degrees of CRF and examined the distribution of the various molecular mass fractions of these proteins in uremic serum. In brief, serum was obtained from 15 healthy volunteers, 17 patients with CRF, 11 patients undergoing maintenance hemodialysis (HD), and 7 patients undergoing peritoneal dialysis (PD). Serum sFas and sFasL were measured by enzyme-linked immunosorbent assay, and their molecular distribution was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by immunoblot. Compared with results in healthy control subjects, sFas levels were significantly higher in patients with CRF and in patients undergoing dialysis. There was a significant inverse correlation between sFas levels and creatinine clearance. Serum sFasL levels were not different among the four groups. However, the sFas-to-sFasL ratio was significantly lower in healthy control subjects as compared with patients with CRF and patients undergoing dialysis. Immunoblots and densitometric analyses of sFas and sFasL depicted a known 48-kd sFas, a known 27-kd sFasL, and a 60-kd sFas-sFasL protein aggregate signal. In conclusion, serum sFas levels are increased in patients with various degrees of CRF and may bind circulating sFasL, thereby minimizing mediation of cellular apoptosis.

Measurement of soluble Fas antigen and ligand in circulating serum and intra-abdominal or cerebrospinal fluid during gastrointestinal or cerebrovascular surgery

PURPOSE

Soluble Fas antigen (sFas) and ligand (sFasL), which are associated with apoptosis, have not been evaluated in gastrointestinal or cerebrovascular surgery. The aim of this study was to measure these substances in serum, intra-abdominal fluid, or cerebrospinal fluid, and to speculate a pathophysiologic role for Fas-FasL apoptosis in surgery.

MATERIALS AND METHODS

Arterial blood and intraabdominal or cerebrospinal fluid were collected at intervals from 27 gastrointestinal surgical patients, 10 cerebrovascular surgical patients, and 10 spinal anesthesia patients.

RESULTS

Serum sFas levels did not change during and after surgery. Intra-abdominal and cerebrospinal sFas levels were identical to and lower than those in serum. Serum sFasL levels did not change during surgery, but decreased after surgery. Intra-abdominal and cerebrospinal sFasL levels were higher than and identical to those in serum. In spinal anesthesia, cerebrospinal sFas and sFasL levels were lower than those in serum.

CONCLUSIONS

Serum sFasL decreases after surgery, whereas intra-abdominal or cerebrospinal sFasL increases, although sFas in each site does not change, suggesting redistribution of activated lymphocytes into local surgical wounds and induction of apoptosis in this site.

Modulation of fas-ligand (Fas-L) on human microglial cells: an in vitro study

The expression of Fas-Ligand (Fas-L) on microglia could be relevant in multiple sclerosis immunopathology. The present study was performed to evaluate in vitro the expression of Fas-L in human microglial cells both unstimulated and after stimulation with IFN-gamma, beta-IFN-1b and beta-IFN-1b+IFN-gamma. Cells were stimulated for 6,12, 24 and 48 h. Surface Fas-L was evaluated by flow cytometry, total Fas-L by Western blot, whereas mRNA for Fas-L was measured by RT-PCR. We also evaluated the capacity of microglial cells to induce, in vitro, apoptosis on Fas-positive T leukemia Jurkat cells. Our results showed a constitutive expression of Fas-L on microglia. IFN-gamma downregulated the expression of the molecule, while beta-IFN-1b and beta-IFN-1b+IFN- gamma did not. The amount of surface Fas-L was related to the ability of microglial cells to induce apoptosis in Fas-positive target cells, which was partly inhibited by blockade of the Fas-Fas-L pathway.

Serum levels of soluble Fas correlate with indices of organ damage in systemic lupus erythematosus

OBJECTIVE

To evaluate whether the levels of soluble form of the Fas apoptosis antigen (sCD95/sFas) varied from those of healthy control subjects in a group of patients with systemic lupus erythematosus (SLE). This was done to determine whether sFas has a role in either the disease activity or the organ damage in SLE.

METHODS

Serum levels of sFas were measured over a period of 4 y (277 determinations) in 39 Arab patients with SLE and 22 age-, gender-, and race-matched healthy controls using double antibody ELISA. SLEDAI scores for disease activity and SLICC/ACR scores for cumulative organ damage were determined. Serum levels of acute phase reactants, complement, inflammatory cell counts, levels of autoantibodies, and kidney and liver function test results were obtained retrospectively from clinical records.

RESULTS

sFas levels were significantly higher in patients with SLE (n = 39, 277 determinations) (0.60 ng/ml +/- 0.38) than in healthy controls (n = 22) (0.26 ng/ml +/- 0.11) (P < 0.00001). The levels of sFas correlated with SLICC/ACR (r = 0.36; P < 0.02), but not with SLEDAI. sFas correlated with renal and liver function tests measured by s-creatinine (r = 0.38; P < 0.0001), creatinine clearance (r = -0.30, P < 0.001), s-albumin (r = -0.28, P < 0.0001), and ALT (r = 0.35; P < 0.00001), but did not correlate with the levels of acute phase reactants.

CONCLUSION

sFas is elevated in sera of SLE patient. Since sFas correlates with indices of organ damage but not with disease activity, it may be a marker of organ damage in SLE and may act to protect certain organs from further damage by inhibiting Fas-mediated apoptosis.

gammadelta T cells of human early pregnancy decidua: evidence for cytotoxic potency

The immune compromise in decidua allows a semiallogeneic fetus to survive without impairing the ability of the maternal immune system to fight infections. Cytotoxic mechanisms are likely to be important in this compromise. Using RT-PCR, immunoflow cytometry and immunoelectron microscopy, the cytotoxic potential of isolated human decidual gammadelta T cells was studied. mRNA for perforin (Pf), granzymes A and B, granulysin and Fas ligand (FasL) was simultaneously expressed in decidual gammadelta T cells. Pf and FasL were not expressed on the cell surface. However, the cells constitutively synthesized Pf and stored it in cytolytic granules. Within the granules Pf mainly resided in the granule core formed by Pf-containing microvesicles. Ultrastructurally, three groups of Pf-containing granules were distinguished. They probably represent different stages of granule maturation in a process where Pf-containing microvesicles first attach to the core cortex and then are translocated across the cortex into the core. Presynthesized FasL was also stored in the core and microvesicles of the cytolytic granules. Upon degranulation by ionomycin/Ca(2+) treatment, FasL was rapidly translocated to the cell surface, demonstrating that its surface expression was not controlled by de novo biosynthesis. Thus decidual gammadelta T cells appear to perform Pf- and FasL-mediated cytotoxicity utilizing a common secretory mechanism based on cytolytic granule exocytosis. The first cytochemical visualization of lipids in the cytolytic granules is provided. These intragranular lipids probably wrap up the core and participate in packaging of the cytotoxic proteins as well as in the killing process. An ultrastructural model of a cytolytic granule is presented.

Expression of Fas and Fas ligand after experimental traumatic brain injury in the rat

Apoptotic cell death plays an important role in the cascade of neuronal degeneration after traumatic brain injury (TBI), but the underlying mechanisms are not fully understood. However, increasing evidence suggests that expression of Fas and its ligand (FasL) could play a major role in mediating apoptotic cell death in acute and chronic neurologic disorders. To further investigate the temporal pattern of Fas and FasL expression after experimental TBI in the rat, male Sprague Dawley rats were subjected to unilateral cortical impact injury. The animals were killed and examined for Fas and FasL protein expression and for immunohistologic analysis at intervals from 15 minutes to 14 days after injury. Increased Fas and FasL immunoreactivity was seen in the cortex ipsilateral to the injury site from 15 minutes to 72 hours after the trauma, respectively. Immunohistologic investigation demonstrated a differential pattern of Fas and FasL expression in the cortex, respectively: increased Fas immunoreactivity was seen in cortical astrocytes and neurons from 15 minutes to 72 hours after the injury. In contrast, increased expression of FasL was seen in cortical neurons, astrocytes, and microglia from 15 minutes to 72 hours after impact injury. Concurrent double-labeling examinations using terminal deoxynucleotidyl transferase-mediated deoxyuridine-biotin nick end labeling identified Fas- and FasL-immunopositive cells with high frequency in the cortex ipsilateral to the injury site. In contrast, there was no evidence of Fas- and FasL-immunopositive cells in the hippocampus ipsilateral to the injury site up to 14 days after the trauma. Further, Fas and FasL immunoreactivity was absent in the contralateral cortex and hippocampus at all time points investigated. These results reveal induction of Fas and FasL expression in the cortex after TBI in the rat. Further, these data implicate an involvement of Fas and FasL in the pathophysiologic mechanism of apoptotic neurodegeneration after TBI. Last, these data suggest that strategies aimed to repress posttraumatic Fas- and FasL-induced apoptosis may open new perspectives for the treatment of TBI.

Immune effects of blood transfusion

Blood is a complicated tissue that has been routinely applied over the past century. Since the recognition of the principles of species specificity (1818) and major compatibility for red cell antigens (1900), considerable attention has been given in the second half of this century to leukocyte-determined immune effects following transfusion. Most reactions are febrile and nonhemolytic and show, in limited situations, true relation to immune activity of transfused white blood cells. The complete picture is not yet finished; however, the more important immune effects are stimulation and modulation, tolerance and suppression. Here most work done is ex vivo and in animal experiments. Little clinical evidence has been obtained or assessment done. Most publications therefore relate to laboratory work, extrapolating results to the bedside. The most interesting publication over the review period with regard to the core immune effects of blood transfusion relates to measured concentrations of active, soluble molecules like HLA class I and II and Fas ligand molecules and to their in vitro immunomodulating effect as well as effects on induction of apoptosis. Stored red cell preparations show an increase in soluble molecules and death of viable leukocytes. Platelet preparations show similar phenomena, although information on numbers of white blood cells and storage conditions are lacking. The authors propose selective use of these aged components in specific clinical settings to allow immune suppression, induction of cell anergy, and apoptosis, whereas fresher products not showing increased levels of soluble molecules could be applied in clinical settings in which immunosuppression is not wanted. No reference is found to scientifically support and substantiate the global universal leukodepletion movement.

Storage of blood components

Recent studies have shown that a restrictive transfusion policy results in lower mortality in patients undergoing surgery. The negative effects of red cell transfusion are associated with the presence of contaminating leukocytes, leukocyte products, and probably also with effects of nonviable and poorly functioning red cells. By relatively simple means it is possible to improve the quality of red cells in these respects. The removal of leukocytes from platelet concentrates (PCs) is even more important because of high immunogenicity and capacity to produce cytokines under the storage conditions applied. Prestorage leukocyte removal has clear advantages. Bacterial contamination of PCs is common, but fatal bacterial complications are rare because most contaminating microorganisms grow slowly and do not produce toxins, which are frequent causes of death. Suitable methods for routine bacterial culture of PCs are available and used in some countries.

Phagocytosis Triggers Macrophage Release of Fas Ligand and Induces Apoptosis of Bystander Leukocytes

Human monocyte/macrophages (Mφ) exposed to nonparticulate stimuli can express cell surface Fas ligand (FasL) and release active soluble FasL (sFasL). We now report that monocyte/Mφ-ingesting opsonized zymosan released sFasL and conditioned supernatants so that these triggered Fas-mediated apoptosis of “bystander” monocytes and FasL-negative neutrophils. Furthermore, identical results were seen with Mφ taking up apoptotic neutrophils, whereas medium conditioned by Mφ phagocytizing latex beads had no proapoptotic effects upon neutrophils despite the presence of sFasL. These data suggest the hitherto unrecognized existence of a feedback loop requiring soluble factors in addition to sFasL that may promote resolution of inflammation-phagocytic clearance of apoptotic cells leading to Fas-mediated killing of bystander leukocytes by phagocytizing macrophages.