A case of maternal-foetal chimerism identified during routine histocompatibility testing for hematopoietic stem cell transplantation.

This report describes a case of maternal-foetal chimerism identified in a boy diagnosed with SCID, who underwent HLA testing in preparation for HSCT. The first analysis was carried out on DNA from peripheral blood and included HLA-A, HLA-B, HLA-DRB1 typing using PCR-SSO. The patient's HLA-B typing results were noninterpretable. All samples were re-typed for HLA-B using PCR-SSP, again resulting in noninterpretable typing of patient's HLA-B. In both cases, several weak positive probes/reactions interfered with the interpretation when using commercial software. Next round of HLA typing, using PCR-SSP and PCR-SSO methods, included the patient's bone marrow sample and HLA-C locus, but interpretation was again not possible. The PCR-STR analysis performed on both peripheral blood and bone marrow samples revealed seven STRs for which two maternal and one paternal allele were detected. Retrospective manual interpretation of HLA-B and HLA-C typing revealed that weak positive reactions were indeed owed to paternal HLA-B and HLA-C alleles and that the patient had both maternal and one paternal allele. Retyping of HLA-B and HLA-C loci and STR analysis on the patient's buccal cells sample revealed the expected one maternal/one paternal allele pattern. In summary, the combination of several different typing methods and manual interpretation were necessary to obtain the patient's HLA typing results.

Lupus nephritis in Croatian children: clinicopathologic findings and outcome.

We report clinical and histopathological features, treatment and outcome of 37 Croatian children with biopsy-proven lupus nephritis seen over a 30-year period. The mean age at lupus nephritis presentation was 12.11 ± 2.59 years (range 4.66-17.0). The most frequent histopathological finding was class IV (37.8%), followed by class III (35.1%), class V (16.2 %) and class II (10.8 %) lupus nephritis. Compared with other classes there were more boys among patients with class IV lupus nephritis, and hypertension, nephrotic syndrome and decreased estimated glomerular filtration rate at presentation were more common. The median histopathological activity and total scores were highest in class IV lupus nephritis patients. The mean follow-up was 7.14 ± 4.71 years, ranging from 1.1 years to 21.0 years. Kaplan-Meier estimate S: of patient and kidney (without renal failure) survival rate S: were 90.5% and 87 % at five years. The renal survival rate of class IV lupus nephritis patients was found significantly lower compared with other histological classes combined. Decreased estimated glomerular filtration rate at the time of diagnosis, class IV lupus nephritis versus other lupus nephritis classes, and high total histological score were the parameters significantly associated with adverse outcome. The therapy with cyclophosphamide showed as superior to the therapy with azathioprine.

Increased frequency of micronuclei in mononucleated lymphocytes and cytome analysis in healthy newborns as an early warning biomarkers of possible future health risks.

Impact of intrauterine development on health risks during adolescence and adulthood still needs to be investigated. The aim of study was to compare genome damage in newborns and mothers using the cytokinesis blocked micronucleus assay, nuclear division index (NDI), and centromere fluorescence in situ hybridization. The study was performed on 92 mothers and their newborns. Results showed that micronucleus frequency in binuclear T-lymphocytes (MNBN) in newborns was significantly lower than in mothers but higher in mononuclear T-lymphocytes (MNMONO). The NDI in the mothers was significantly higher than in the newborns. In newborns with <2500g birth weight, NDI was similar to the mothers'. Mothers have significantly more centromere negative micronuclei than newborns. A significantly higher NDI and MNBN was found in newborns with ≥2 MNMONO/1000 than in newborns with <2 MNMONO/1000. It is suggested that MOMN and NDI might be good candidates for biomarkers of health risks in newborns.

Toxicity related to autologous peripheral blood haematopoietic progenitor cell infusion is associated with number of granulocytes in graft, gender and diagnosis of multiple myeloma.

BACKGROUND AND OBJECTIVES: We prospectively evaluated the infusion-related toxicity of autologous peripheral blood progenitor cells (PBPC) in 215 patients with haematologic malignancies or solid tumours. MATERIALS AND METHODS: PBPCs were collected by apheresis after mobilization with chemotherapy and/or granulocyte-colony-stimulating factor (G-CSF). The grafts were cryopreserved in 10% dimethyl sulfoxide (DMSO) and stored in liquid nitrogen. Patients were monitored for vital signs and symptoms of the toxicity during and after infusion. RESULTS: The adverse reactions were reported during 149 (56.9%) infusions. During 21.0% infusions occurred just one symptom classified as grade 1, while during 35.9% occurred multiple symptoms classified as grade 2. Logistic regression analysis showed that female gender, diagnosis of multiple myeloma and number of granulocytes infused per kg body weight were significant predictors of occurrence of adverse reactions during infusion. CONCLUSION: Our results indicate that beside the infused DMSO dose, the composition of graft as well as patient's diagnosis are also very important factors for infusion-related toxicity.

Lithium increases expression of p21(WAF/Cip1) and survivin in human glioblastoma cells.

Lithium is the most widely prescribed mood stabilizer, but the precise molecular mechanisms underlying its therapeutic function are not yet fully elucidated. Recent preclinical and clinical evidence indicates its neuroprotective and neurotrophic effects. As a tight coupling of function and metabolism in the central nervous system between glial cells and neurons has recently been detected, lithium's effect on glial cells may participate also in the total beneficial effects of this drug. The aim of the present study was to analyze molecular mechanisms induced in human glioblastoma A1235 cells by the treatment with lithium, especially its influence on the expression of apoptosis-related genes. Lower levels of lithium (0.5 mmol/L and 2 mmol/L) did not cause any cytotoxicity or changes in the cell cycle phase distribution following 72 h incubation. However, a higher dose (20 mmol/L) was cytostatic for glioblastoma cells, and caused accumulation of cells in G(2)/M phase of the cell cycle. The treatment with lithium did not alter the levels of Bcl-2 or procaspase-3 and did not cleave PARP, but increased the levels of p21(WAF/Cip1) and survivin. Thus, increased expression of p21(WAF/Cip1) (a protein with antiapoptotic function), and survivin (a protein that supports the growth of cells by suppression of apoptosis and promotion of cell proliferation) may be the early events in the long-term cell response to lithium that are involved in the beneficial effects of this drug.

IgH and TCRgamma gene rearrangements, cyclin A1 and HOXA9 gene expression in biphenotypic acute leukemias.

In this study we investigated IgH and TCRgamma gene rearrangements, cyclin A1 and HOXA9 gene expression as well as the in vitro growth of biphenotypic acute leukemia (BAL) blasts in relation to acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML). The aim of the study was to correlate BAL morphology and its biological parameters in order to get information that might be used for additional stratification of BAL. This rare form of AL was identified in a total of 10 patients, comprising 4.3% of adult and 3.0% of pediatric patients with de novo AL referred to our institution during the 1999-2003 period. Our results indicate that IgH and TCRgamma gene rearrangements correlated well with lymphoid BAL morphology, whereas the expression of cyclin A1 correlated with myeloid and undifferentiated BAL morphology. Surprisingly, HOXA9 expression, a marker associated with myeloid cell lineage, showed no strong correlation with BAL morphology. Finally, in vitro growth of blasts during a 7-day culture showed autonomous cell growth in 3/10 AML and 3/8 myeloid BAL samples tested, but not in any of the AL with lymphoid features. Further studies are needed to confirm these findings and to extend research to a broader spectrum of cell markers.

The value of urine citrate/calcium ratio in the estimation of risk of urolithiasis.

The urine saturation is considered as the better parameter for the estimation of risk of urolithiasis than any single urinary constituent. However, the determination of urine saturation is unsuitable for routine clinical practice. To evaluate a simpler and cheaper test than urine saturation for distinguishing stone formers from healthy individuals, urinary citrate/calcium ratio was determined in 30 children with urolithiasis, 36 children with isolated hematuria, and 15 healthy control children. The ratio was significantly lower in urolithiasis group comparing to controls, and significantly higher in hematuria than in urolithiasis group. The cut-off points between normal children and children with urolithiasis, accuracy, specificity and sensitivity were determined and compared with those of the urine saturation calculated with the computer program EQUIL 2. The data mining Weka software was used for the determination of the cut-off points. Children with urolithiasis had citrate/calcium ratio below 1.38 and urine saturation above 5.285. The citrate/calcium ratio showed in comparison to urine saturation similar high accuracy (91.11 vs. 88.89%), somewhat lesser specificity (73.33% vs. 93.33%) and much better sensitivity (100% vs. 86.89%) in discrimination of stone formers from normal children. The advantage in comparison to urine saturation is that it can be easily performed in clinical practice.

Thiorphan, an inhibitor of neutral endopeptidase/enkephalinase (CD10/CALLA) enhances cell proliferation in bone marrow cultures of patients with acute leukemia in remission.

Thiorphan, (DL-mercapto-2-benzylpropanoyl)-glycine is a potent and specific inhibitor of membrane metallo-endopeptidase (EC 3.4.24.11, CD10). We explored its effects in short-term clonal cultures of the bone marrow from 10 patients with acute leukemia in remission. The cell suspensions were incubated with thiorphan (10(-13) to 10(-5) M) and seeded for the granulocyte/macrophage-colony forming unit (GM-CFU) assay. In normal bone marrow samples the median seeding efficiency was 119 colonies and clusters per 10(5) cells and thiorphan caused slight stimulation of the clonal growth in concentrations above 10(-9) M. In the leukemic samples, the median seeding efficiency varied from 10 to 366 colonies and clusters per 10(5) seeded cells. Meaningful alterations of the clonal growth were noted in 32 out of 83 thiorphan-treated cultures (39%). In those 32 cultures the stimulatory effects outnumbered the inhibitory effects (24 versus 8). Thus, thiorphan stimulated the progenitor cell proliferation in bone marrow samples from the normal donor and from the patients with acute leukemia in remission. Thiorphan binding to CD10 might interfere with the processing of neuropeptide hemoregulatory factors and thus influence the progenitor cell proliferation.

Value of the urinary stone promoters/inhibitors ratios in the estimation of the risk of urolithiasis.

An imbalance between urinary-promoting and -inhibiting factors has been suggested as more important in urinary stone formation than a disturbance of any single substance. To investigate the value of promoter/inhibitor ratios for estimation of the risk of urolithiasis, urinary citrate/calcium, magnesium/calcium oxalate, and oxalate/citrate x glycosaminoglycans ratios were determined in 30 children with urolithiasis, 36 children with isolated hematuria, and 15 healthy control children. The cutoff points between normal children and children with urolithiasis, accuracy, specificity, and sensitivity for each ratio were determined and compared with those of the 24-h urine calcium and oxalate excretion and urine saturation calculated with the computer program EQUIL 2. The neural network application (aiNET Artificial Neural Network, version 1.25) was used for the determination of the cutoff points for the classification of normal children and the urolithiasis group. The best test for differentiating stone formers from non-stone formers proved the aiNET determined cutoff values of oxalate/citrate x glycosaminoglycans ratio. The method showed 97.78% accuracy, 100% sensitivity, and 93.33% specificity. Two cutoff points between normal and urolithiasis groups were found showing that the children with urolithiasis had ratio values either above 34.00 or less than 10.16. Increased oxalate excretion was linked to the first cutoff value (34.00), and decreased glycosaminoglycans excretion was typical of the second cutoff value (10.16).

Different roles of protein kinase C alpha and delta isoforms in the regulation of neutral sphingomyelinase activity in HL-60 cells.

The signalling mechanisms responsible for the hydrolysis of sphingomyelin mediated by 1,25-dihydroxyvitamin D(3) [1, 25(OH)(2)D(3)] and interferon gamma (IFN-gamma) in HL-60 cells were investigated. IFN-gamma was found to increase selectively the activity of cytosolic, Mg(2+)-independent, neutral sphingomyelinase. The treatment of HL-60 cells with the combination of 1,25(OH)(2)D(3) and IFN-gamma had an additive effect on sphingomyelin hydrolysis, ceramide release and the activity of cytosolic, Mg(2+)-independent, neutral sphingomyelinase. The pretreatment of HL-60 cells with staurosporine, chelerythrine chloride and bisindolylmaleimide abolished the activity of sphingomyelinase in response to 1,25(OH)(2)D(3) and IFN-gamma. Calphostin C, which acts on the regulatory site of protein kinase C (PKC), and Gö 6976, a selective inhibitor of Ca(2+)-dependent PKC isoforms, inhibited the effect of 1,25(OH)(2)D(3) but had no effect on the IFN-gamma-mediated increase in activity of sphingomyelinase. Isoform-specific antibodies were used to deplete different PKC isoforms from cytosol before the treatment of the cytosolic fraction with 1,25(OH)(2)D(3), arachidonic acid (AA) and PMA. The depletion of PKC isoforms beta(1), beta(2), epsilon, eta, mu, zeta and lambda had no effect on the activation of sphingomyelinase induced by 1,25(OH)(2)D(3) or by AA. The depletion of PKC alpha from the cytosol completely abolished the effect of 1,25(OH)(2)D(3) on sphingomyelinase activity but had no effect on the AA-induced activity of sphingomyelinase. PMA had no effect on the activity of sphingomyelinase in either untreated or alpha-depleted cytosol but significantly increased the activity of sphingomyelinase when added to cytosol depleted of PKC delta. Moreover, PMA inhibited the effect of 1,25(OH)(2)D(3) on sphingomyelinase activation but the inhibitory effect was abolished by prior depletion of PKC delta from the cytosol. These studies demonstrate that 1,25(OH)(2)D(3)-induced activation of sphingomyelinase is mediated by PKC alpha. Furthermore, PKC delta had an inhibitory effect on sphingomyelinase, suggesting that the difference between the 1,25(OH)(2)D(3)- and PMA-mediated effects on sphingomyelin turnover depends on the specific regulation of the PKC alpha and PKC delta isoforms.

Quantity and origin of transplanted autologous blood cells are independent factors associated with speed of postransplant hematological reconstitution.

AIM: Multivariate analysis of the prognostic significance of clinical and laboratory parameters on hematological recovery after autologous hematopoietic stem cell transplantation. METHODS: Sixty-two patients suffering from hematological and non-hematological malignancies entered the study. After conditioning therapy, 28 patients received bone marrow stem cells, 21 received peripheral blood stem cells, and 13 received both. The dynamic of hematological engraftment was calculated as recovery probability of leukocytes and neutrophils. Statistics was done using Kaplan-Meier method and multivariate Cox's proportional regression. RESULTS: Numerous clinical and laboratory parameters correlated with hematological recovery, but only two variables were found to be independently associated. Faster reconstitution correlated with greater number of progenitors and patients who received bone marrow cells recovered significantly later than others. Faster recovery could be expected in patient s receiving >13x10(4) CFU-GM/kg body weight, and significantly slower in those receiving <8.5x10(4) CFU-GM/kg. CONCLUSION: The quantity of progenitor cells and transplant type are variables significantly associated with the speed of postransplant engraftment, but these two parameters are mutually independent. The number of stem cells estimated by CFU-GM assay is a good and reliable routine test for predicting hematopoietic recovery.

Pre-treatment of transplant bone marrow cells with hydrocortisone and cyclosporin A alleviates graft-versus-host reaction in a murine allogeneic host-donor combination.

The aim of the study was to alleviate graft-versus-host reaction (GVHR) by pre-treatment of the bone marrow (BM) transplant with hydrocortisone (HC) and cyclosporin A (CsA) in C57BL/6J (donor) --> CBA/J (recipient) mouse combination. BM cells were exposed to HC and CsA for 1 h at 37 degrees C and then injected into lethally irradiated (9.5 Gy) mice at a dose of 2 x 10(6) BM cells/mouse. Haematopoietic recovery was assessed on day 12, and survival was followed for 100 days. Combinations of 1000 microg/ml HC and 100 microg/ml CsA, and 100 microg/ml HC and 10 microg/ml CsA significantly reduced MLR and additively mitigated GVHR in vivo, achieving 40% and 26% survival rates, respectively. However, HC and CsA altered neither the peripheral blood cell counts nor in vitro and in vivo BM cell clonogenic potential. Additional studies have shown that HC and CsA blocked con A-driven differentiation of CD8+ and CD4+ CD8+ lymph node cells (LNC) and progression of LNC to S + G2/M cell cycle phases, and inhibited IL-1, IL-2 and TGF-beta while enhancing GM-CSF gene expression in BM cells. Taken together, these data indicate that the pre-treatment of the BM transplant with HC and CsA results in inactivation of GVHR effector cells and mitigation of GVHR while sparing BM repopulating capacity.

Tc-99m DTPA renal scintigraphy using deconvolution analysis with six functional images of the mean time to evaluate acute pyelonephritis.

In 38 children with proved P-fimbriated Escherichia coli acute pyelonephritis, Tc-99m DTPA dynamic renal scintigraphy in the zoom mode using deconvolution analysis was performed, and the results were compared with those of Tc-99m DMSA scans. From the dynamic study, six functional images of the mean time were generated. Each functional image was analyzed separately to search for focal areas of increased mean time within the kidney contour, especially over the kidney parenchyma. Time-activity curves from these areas were generated and analyzed. Tc-99m DMSA scintigraphy showed generalized or focal decreased uptake in 32 (41.8%) kidneys, and deconvolution analysis of Tc-99m DTPA scintigraphy revealed pathologic renographic curves in 58 (77.6%) kidneys. Prolonged whole-kidney and normal renal parenchymal transit times (dilatation without obstruction) were found in 38 (50%) kidneys, whereas prolonged whole-kidney and renal parenchymal transit times (dilatation with obstruction) were observed in 20 (27.6%) kidneys. Separate analysis of each of the six functional images of the mean time showed focal areas of increased mean time in the kidney parenchyma of 11 kidneys. In five cases, time-activity curves from these areas showed a sharp increase of activity on the descending part of the curve, which might reflect the return of urine from the collecting system into kidney cortex (i.e., intrarenal reflux). These results showed that in a urinary tract with acute pyelonephritis, urodynamic changes may lead to obstructive nephropathy and intrarenal reflux. Tc-99m DTPA renal scintigraphy in the zoom mode using deconvolution analysis with six functional images of the mean time has proved to be a valuable method to evaluate acute pyelonephritis, thus allowing dynamic and morphologic analysis of the urinary tract at the same time.

Double immunoenzymatic APAAP staining for the detection of leukemia-associated immunophenotypes.

Detection of unusual or aberrant cell immunophenotype with flow cytometry is the basis for the immunologic recognition of minimal residual disease (MRD) in patients with acute leukemia (AL). In this study, we have shown that the double immunocytochemical alkaline phosphatase antialkaline phosphatase (APAAP) staining technique also makes possible the detection of leukemic cells with unusual (leukemic) combinations of antigens (ULCA) both at diagnosis and during follow-up of patients with ULCA+ AL. The applicability of double APAAP was analyzed on bone marrow (BM) samples obtained from 12 patients (8 with AML, 3 with ALL, and 1 with undifferentiated acute leukemia [AUL]) randomly chosen from a larger group of 22 ULCA+ patients treated at our center in a 3-year period (22% observed ULCA+ AL frequency). The percentages of ULCA+ BM cells before chemotherapy were in the range of 5%-60%, which dropped to 0%-7% in 10 patients who achieved remission (range 0%-7%, p < 0.01). However, these cells could also be found 60 days after the initiation of therapy, ranging from 0%-2% of all nucleated cells. In 2 of 10 patients who achieved remission, 2% ULCA+ BM cells were found on days 35 and 60 after initiation of chemotherapy, and this finding was followed by relapse on days 110 and 270. However, the other 8 patients remained in remission despite positive finding of ULCA+ BM cells ranging from 0.2%-2% on at least one occasion. In 2 patients with AML FAB-M3 and cytomorphologic remission, the finding of ULCA+ cells by double APAAP correlated with the molecular finding of PML/RARalpha junction. These results indicate that double APAAP staining can identify leukemic cells in samples with a cytomorphologic pattern consistent with remission, but its applicability in detection of MRD awaits additional studies on a larger number of patients with ULCA+ AL.

Thiorphan stimulates clonal growth of GM-CFU in short-term cultures of bone marrow from a healthy donor and from patients with non-Hodgkin lymphoma.

Thiorphan, a specific inhibitor of membrane neutral endopeptidase (NEP, EC 3.4.24.11) also known as the common acute lymphoblastic leukemia antigen (CALLA, CD10) was added into short-term clonal cultures of the buffy coat concentrates of human bone marrow obtained from a healthy donor (six experiments) and from ten patients with non-Hodgkin lymphoma (NHL) (eight in complete remission, one in partial remission and one in relapse). Thiorphan concentrations ranged from 10(-5) to 10(-13) M. Nanomolar and higher concentrations of the drug mildly stimulated the granulocyte-macrophage colony-forming unit (GM-CFU) counts in the cultures of normal bone marrow, reaching the significance at 10(-7) M. Meaningful alterations of the GM-CFU counts were noted in 31 of 79 thiorphan-treated cultures of NHL bone marrow (39%). In those cultures the stimulatory effects (33%) outnumbered the inhibitory ones (6%). The stimulatory effects occurred mainly in the bone marrow samples of the patients with highly malignant NHL. The observations are compatible with the idea that the membrane endopeptidase (CALLA, CD10) participates in processes controlling the proliferation and differentiation of hematopoetic cells by cleaving the neuropeptides and related hemoregulatory peptides.

Determination of urine saturation with computer program EQUIL 2 as a method for estimation of the risk of urolithiasis.

To investigate the risk for the development of urolithiasis in 30 children with urolithiasis, 36 children with isolated hematuria, and 15 healthy control children, 24-h urinary excretion of calcium, sodium, oxalate, citrate, sulfate, phosphate, magnesium, urate, chloride, ammonium, and glycosaminoglycans was determined and urine saturation for calcium oxalate was calculated with the computer program EQUIL 2. Compared with controls, children with urolithiasis had significantly increased calcium excretion, oxalate excretion, and urine saturation, whereas children with isolated hematuria had significantly increased calcium excretion only. The best estimation of the relative risk of urolithiasis can be made after urine saturation, using logistic regression. The percentage of patients correctly classified after urine saturation is 85.41% in comparison with 80.95% and 73.81% when the estimation was done by calcium excretion and oxalate excretion, respectively. Using the breakpoint value of 4.29 for urine saturation, it was possible to separate children with increased risk of urolithiasis development from the group of children with isolated hematuria.

Organochlorine pesticides and PCBs in human milk collected from mothers nursing hospitalized children.

Organochlorine compounds in milk were analyzed in samples collected over a nine-year period (1987-1995) from nursing mothers (N = 139) whose children were hospitalized for various disorders. All samples contained p,p'-DDE and PCBs; the median concentrations were 318 micrograms/kg milk fat and 220 micrograms/kg milk fat resp. Higher levels were found in mothers (N = 12) nursing neonates with impaired neurodevelopmental competencies or an inappropriate arousal reaction. No difference was observed between mothers nursing children with respiratory or gastrointestinal diseases, urinary tract infections or other infectious diseases, anemias, prolonged neonatal hyperbilirubinaemias or when children were with dermatological findings, congenital malformations or healthy.

Indirect demonstration of the lifetime function of human thymus.

The aim of this study was to test the hypothesis that human thymus maintains its function as the site of early T cell development throughout life, but to a progressively diminishing extent. Mononuclear cell suspensions prepared from the samples of 39 human thymuses were analysed for the total number of cells per gram of thymus tissue, percentage of single marker-positive CD2, CD4 and CD8 cells, percentages of double-positive CD4CD8 and CD2CD8 cells, double-negative CD4CD8 cells, absolute numbers of these cells per gram of tissue, and extent of the in vitro proliferation upon stimulation with concanavalin A (Con A), phytohaemagglutinin (PHA) and pokeweed mitogen (PWM) mitogens. The main outcome measures were flow cytometric data on thymus lymphoid cell composition (according to CD classification), expressed as percentages and numbers of cells per gram of thymus tissue. The total number of mononuclear cells expressed per gram of thymus tissue exponentially decreased with age. The slope of none of the analysed cell subpopulations differed from the slope of the line constructed for age-related decline of the total number of mononuclear cells (-0.024 on a semilogarithmic scale). The thymuses of all ages contained all analysed cell subpopulations in approximately the same proportions: percentages of these cell subpopulations did not change with age, except for all CD4+ (P=0.017) and double-positive CD4+CD8+ (P=0.016) cells, which tended to decrease with age. The extent of proliferation of thymus cells upon stimulation with T and B cell mitogens was unrelated to age. We conclude that the thymus retains its function as the site of differentiation of T lymphocytes throughout life. With respect to the number of involved lymphoid cells, the function exponentially decreases with age.

Arachidonic acid mediates interferon-gamma-induced sphingomyelin hydrolysis and monocytic marker expression in HL-60 cell line.

The biochemical signaling mechanisms involved in transducing the effects of interferon-gamma (IFN-gamma) on human leukemia-derived HL-60 cell differentiation are not completely understood. Recent studies established the existence of a sphingomyelin (SM) cycle that operates in response to the action of IFN-gamma on HL-60 cells, but the mechanisms by which IFN-gamma induces the SM hydrolysis remain unexplored. In this study, biochemical events mediating IFN-gamma effects on SM turnover and their specificity and role in HL-60 differentiation were investigated. The activation of the SM cycle by IFN-gamma occurred rapidly, with a decrease of approximately 20% in the SM level observed after 60 minutes with a concomitant increase in ceramide level. Treatment of HL-60 cells with IFN-gamma did not influence the 1,2-diacylglycerol concentration, intracellular Ca2+ concentration, or phospholipase D activity. IFN-gamma stimulated a rapid release of arachidonic acid (AA) from HL-60 cells; the effect was abolished by the pretreatment of cells with pertussis toxin, suggesting a role for a pertussis-toxin-sensitive G protein in IFN-gamma-mediated activation of phospholipase A2 (PLA2). At 4 to 120 hours after the stimulation of the cells with IFN-gamma, a significant increase in the particulate and soluble PLA2 activity was observed, corresponding to an increase in the level of immunoreactive cPLA2 in both cytosol and membrane fractions. The treatment of cells with tyrosine kinase inhibitor herbimycin A completely abolished the effect of IFN-gamma on PLA2 activity in membrane and cytosolic fractions, but had no effect on IFN-gamma-mediated early AA release suggesting dual mechanism of PLA2 activation. Melittin, potent activator of PLA2, and AA mimicked the effect of IFN-gamma on SM hydrolysis. Pretreatment of HL-60 cells with the PLA2 inhibitor, bromophenacyl bromide (BPB), or pertussis toxin abolished the effect of IFN-gamma on SM hydrolysis; exogenous addition of AA overcame the effects of BPB and pertussis toxin. Long-term exposure (5 days) of HL-60 cells to IFN-gamma caused an increase in nitroblue tetrazolium (NBT)-reducing and nonspecific esterase (NSE) activity and induced expression of Fc gamma RI (CD64) without significant effects on cell number, adherence, or phagocytic activity. The treatment of cells with AA or melittin induced NBT, NSE, and CD64 expression to the level similar to that observed with IFN-gamma, and no further increase was observed with the combination of IFN-gamma and AA or IFN-gamma and melittin. Treatment of HL-60 cells with indomethacin, an inhibitor of cyclo-oxygenase, and nordihydroguaiaretic acid (NDGA), an inhibitor of lipoxygenase, had no effects on IFN-gamma-mediated induction of CD64 expression. These studies indicate a key role for the phospholipase A2/AA pathway, as an early biochemical signal elicited by the occupation of IFN-gamma-receptor, in mediating IFN-gamma induction of the SM cycle and phenotypic changes associated with differentiation of HL-60 along monocytic lineage.