N-myc protein expression in human breast carcinoma: prognostic implications

The overexpression of N-myc gene and its protein products has been thought to be limited to cases of neuroblastoma, retinoblastoma and small cell lung carcinoma, but there is increasing evidence of its wider distribution in human tumors. This study showed that the protein of N-myc gene is associated in normal, benign and malignant human breast tissues. We found that N-myc oncoprotein is overexpressed in most breast carcinomas and that N-myc overexpression is significantly correlated with clinical stage, and histological grading of the tumors, and, more importantly with the clinical outcome of the patients. Analysis of DNA, mRNA and protein levels suggested that the high N-myc expression in breast cancer occurs without concomitant gene amplification. The finding of a direct inverse correlation between N-myc overexpression and the prognosis of patients with breast carcinoma suggests that N-myc expression may be useful as a prognostic factor in human breast cancer.

Propranolol inhibits the spontaneous closure of the ductus arteriosus in newborn rats

Newborn rats delivered by cesarean section were given subcutaneously propranolol (PRO), a beta-adrenergic blocker, (1) immediately or (2) 180 min after delivery. The diameter of the ductus arteriosus (DA) of the newborn pups was calibrated at 30, 60 and 90 min after the PRO-administration. The results were as follows: (1) the DA calibers of the pups given 0.2, 1.0., 5.0 mg/kg PRO immediately after cesarean delivery remained significantly larger than those of controls in a dose-dependent manner for 30 min after treatment. In the 5 mg/kg group, the enlargement of the DA was prolonged for 90 min after treatment. (2) In untreated pups, the DA completely closed by 180 min after cesarean delivery. The DA was not affected by the administration of 5 mg/kg PRO at 3 hr after delivery. It was concluded that, PRO inhibits the spontaneous constriction of the DA, suggesting an important role of beta-adrenergic stimulation on the spontaneous closure of the DA in newborn rats.

A case of right atrial myxoma--effect of large myxoma in the right atrium studied by M-mode and Doppler echocardiography

Doppler profiles are rarely used to assess cardiac function that has been partially impaired by a sizeable myxoma in the right atrium or to evaluate the improvement caused by extirpation of the tumor. In a 54-year-old man with a large right atrial myxoma (6.5 x 5.5 x 4.0 cm) along with first-degree atrioventricular (AV) block, M-mode and pulsed Doppler echocardiography were used to evaluate the left ventricular systolic and diastolic function before and 1 month after surgical removal of the myxoma. End-diastolic left ventricular (LV) and left atrial diameters increased postsurgically from 47 to 51 mm and from 38 to 41 mm, respectively, while end-systolic LV remained unchanged. In the LV inflow pattern, peak early filling velocity (E) increased substantially (preoperative 31, postoperative 58 cm/sec), with no change in peak late filling velocity (A) (53 cm/sec), which gave a favorable E/A ratio (from 0.58 to 1.09). First-degree AV block resolved after tumor resection (PR interval: 0.23 vs 0.20 sec). Improved LV diastolic function associated with natural recovery from the myxoma was ascribed to the restoration of preload and recovery of systolic function. The results of this study show that removal of a large myxoma in the right atrium is important not only for preventing possible obstruction of the tricuspid orifice, eliminating pulmonary emboli, and maintaining systolic function, but also for restoring LV diastolic function.

Interaction of the cell-binding domain of fibronectin with VLA-5 integrin induces monokine production in cultured human monocytes

The effect of fibronectin on IL-1 alpha, IL-1 beta, tumour necrosis factor-alpha (TNF-alpha), and IL-6 production was investigated with cultured monocytes isolated from human peripheral blood. Monokine concentrations were determined by both ELISA and bioassay. Fibronectin markedly stimulated the secretion of IL-1 alpha, IL-1 beta, TNF-alpha and IL-6 from cultured monocytes in a dose-dependent manner, with the maximal effect apparent within 24 h. Northern blot analysis revealed a marked increase in the abundance of mRNA specific for each monokine on exposure of monocytes to fibronectin. Monoclonal antibodies to the alpha chain of very late antigen (VLA)-5, the beta 1 integrin, the alpha chain of Mac-1, and the beta 2 integrin, as well as the synthetic peptide of GRGDSP (which corresponds to the cell-binding domain of fibronectin), inhibited (> 50%) fibronectin-induced monokine production. Monoclonal antibodies to the alpha chain of VLA-4, and the alpha chain of LFA-1, as well as the synthetic peptide CS-1 (which corresponds to the alternatively spliced connecting segment of fibronectin) and the control peptide GRADSP, had no inhibitory effect on monokine production. A MoAb, R60, that recognizes an epitope of the fibronectin molecule that includes the RGD sequence, inhibited monokine production, whereas the MoAb Y16, which recognizes another epitope of fibronectin not including RGD, did not. These results indicate that fibronectin-induced production of IL-1 alpha, IL-1 beta, TNF-alpha and IL-6 from cultured monocytes is mediated predominantly by interaction of the cell-binding domain of fibronectin with VLA-5, although Mac-1 also may contribute to this effect of fibronectin. Our results indicate that the interaction of fibronectin with integrins may contribute to the cytokine network in inflammatory response.

Transcription stimulation of the Fas-encoding gene by nuclear factor for interleukin-6 expression upon influenza virus infection

We previously found that the level of Fas, a cell surface receptor for an apoptosis signal, increases at the mRNA level in influenza virus-infected HeLa cells prior to their death by apoptosis. Here we investigated the mechanism of activation of the Fas-encoding gene expression upon influenza virus infection. Nucleotide sequences for the binding of nuclear factor for interleukin-6 expression (NF-IL6), also known as CCAAT/enhancer-binding protein beta, were repeated 8 times in the 5'-end region of the human FAS gene, spanning from -1360 to +320. This region directed the expression of a downstream marker gene when introduced into HeLa cells and the activity of the FAS gene promoter was stimulated about 2-fold upon influenza virus infection. Gene expression driven by the FAS promoter was activated when human NF-IL6 was overproduced in a DNA when human NF-IL6 was overproduced in a DNA co-transfection study. Moreover, the DNA-binding activity of NF-IL6 increased after infection with the virus, whereas the amount of NF-IL6 seemed unchanged. The results suggest that NF-IL6 is activated upon influenza virus infection through post-translational modification and that the modified factor stimulates the transcription of the human FAS gene.

Pharmacokinetics and pharmacodynamics of nisoldipine in hypertensive patients with normal and mild to moderate impaired renal function

The pharmacokinetics and pharmacodynamics of nisoldipine (CAS 63675-72-9, isobutyl methyl 1,4-dihydro-2,6-dimethyl-4-(2-nitrophenyl)-3,5-pyridinedicarboxylate, Bay k 5552), a calcium antagonist, were investigated after administration of a single oral 10 mg dose and after 7 same doses on consecutive days to hypertensive patients with normal renal function (NRF) and those with mild to moderate renal dysfunction (impaired renal function, IRF). A significant decrease in blood pressure was observed after consecutive dosing of nisoldipine compared to baseline values over 24 h in both groups. There were no significant differences in plasma profiles of nisoldipine in both groups after either single or consecutive dosing. The plasma concentration-time profiles of the active metabolite, Bay r 9425, were similar to those of nisoldipine in both groups. The pharmacokinetic parameters of nisoldipine and its active metabolite in the NRF and IRF groups did not differ after the single and the consecutive dosing. In addition, there were neither prolongation of apparent elimination half-life (t1/2), nor increases in peak plasma levels (Cmax), or the area under the plasma concentration-time curve (AUC0-infinity) after consecutive dosing in both groups. Cumulative urinary excretion rates of the major metabolites, Bay s 4755 and Bay s 1869, did not differ significantly between the NRF and IRF groups in both single and consecutive studies. In the present study, mild flushing was observed in one patient with IRF. There was no deterioration in renal function during the study. These results suggest that nisoldipine may have a long-lasting antihypertensive effect during consecutive dosing and that it can be used in hypertensive patients regardless of presence of renal dysfunction.

[Endoscopic mucosal resection for radical treatment of esophageal cancer]

Clinico-pathological results of patients with superficial esophageal cancer was reviewed to determine the indications of endoscopic mucosal resection (EMR) for esophageal cancer as a radical treatment and to evaluate clinical results of EMR. The analysis on eighty-seven cases with superficial esophageal cancer who underwent esophagectomy revealed no lymph node metastasis in any 0% of case with cancer confined to the lamina propria mucosae, 10% of cancer reaching the muscularis mucosae and 43% of cancer infiltrating the submucosa. These results suggested that the endoscopic mucosal resection should be indicated for patients with esophageal cancer confined to the lamina propria mucosae. The accuracy rate for estimating depth of invasion of mucosal cancer of the esophagus was 96%. We early established "the double channel technique" for resection of mucosal lesion of the esophagus with a major part of the submucosa, we used it for sixty-nine cases, and all were eventually discharged. Immediate complications of EMR were noted in 12.9% of all cases (mediastinal emphysema: 2.9%, ulcer bleeding: 10%) and the late complication in 7.2% (esophageal stricture due to scar formation: 5.8% and ulcer bleeding 5 days after EMR: 1.4%). All cases who developed stricture had mucosal defect over 3/4 the circumference. The cumulative 5-year survival rate of patients with esophageal mucosal cancer treated by EMR (86%) showed no significant difference from those treated by esophagectomy (83.2%). We to conclude that endoscopic mucosal resection is indicated for the patient with mucosal cancer confined to the lamina propria mucosae. One can expect an excellent prognosis by less invasive treatment than esophagectomy.

Effects of fructooligosaccharides on the absorption of iron, calcium and magnesium in iron-deficient anemic rats

We investigated the effects of fructooligosaccharides (FO)-feeding on the absorption of iron (Fe), calcium (Ca) and magnesium (Mg) and on the biochemical parameters in Fe-deficient anemic rats. Fe-deficient anemic rats were made by feeding an Fe-deficient diet for 3 weeks. Then these Fe-deficient rats were fed an experimental diet that contained one of two levels of Fe (15 or 30 mg/kg diet), in the form of ferric pyrophosphate, and one of two levels of FO (0 or 50 g/kg diet) for 2 weeks. After the rats were fed these experimental diets, FO-feeding increased the hematocrit ratio, the concentration of hemoglobin and the hemoglobin regeneration efficiency during the first week. Also, the apparent absorption of Fe was increased by FO-feeding. The levels of Fe in the diet did not affect the absorption of Ca and Mg. However, FO-feeding increased the absorption of Ca and Mg. FO-feeding lowered the pH and raised the solubility of Fe, Ca and Mg in the cecal contents, suggesting that those increasing effects of FO-feeding on absorption of these minerals is correlated with fermentation of FO in the large intestine, namely, the cecum and colon. We concluded that FO-feeding improved recovery from anemia and increased the absorption of Fe, Ca and Mg in Fe-deficient anemic rats.

Activation of the apoptotic Fas antigen-encoding gene upon influenza virus infection involving spontaneously produced beta-interferon

We previously demonstrated that influenza virus infection induces apoptosis in culture cells. Here, we examined the activation of the Fas antigen gene that encodes an apoptosis-mediating membrane protein in the virus-infected cells. The virus elicited a transient but marked increase in Fas antigen mRNA 3 to 4 hr after infection, followed by the expression of the antigen on the cell surface. Poly(I)-poly(C), a synthetic double-stranded RNA, similarly activated Fas antigen gene expression, and poly(I)-poly(C)-treated cells are highly susceptible to the cell killing effect of IgM isotype of anti-Fas monoclonal antibody. On the other hand, the IgG isotype of anti-Fas monoclonal antibody, which has an inhibitory effect on Fas Ag-mediated cell death, suppressed the virus-induced cell death. Prior exposure of the cells to anti-interferon-beta antibody decreased the degree of cell death as well as the amount of Fas mRNA. The autophosphorylation activity of double-stranded RNA-activated protein kinase was also decreased in the antibody-treated cells. Moreover, a protein kinase inhibitor, 2-aminopurine, blocked the Fas Ag gene activation by poly(I)-poly(C). These results suggested that the activation of Fas Ag gene in the early phase of infection is an important event for apoptosis, and that it is regulated by the double-stranded RNA/interferon system involving protein phosphorylation.

Morphological changes in gastric carcinoma with progression

By combining morphological two indices, namely, (1) the degree of differentiation of glandular tubules (well or poor) and (2) the amount of intracellular mucus (rich or poor), we previously classified histological types of gastric carcinoma into four types. Using this histological classification, we studied the morphological changes of gastric carcinoma according to extra-gastric invasion in 200 autopsy and 200 resected cases. In cases in which the predominant histological type in the lamina propria was "tubular differentiation--well, mucus in cytoplasm--poor," there was a greater incidence of co-existence with other histological types. In many of these cases, the predominant histological findings changed to "tubular differentiation--poor" in the subserosa, followed by direct invasion into neighboring extra-gastric tissues. In all cases in which the predominant histological type in the lamina propria was "tubular differentiation--poor," the predominant histological type in the subserosa was also "tubular differentiation--poor." To understand the mode of extension of gastric carcinoma in relation to the histological type, we must consider not only the characteristics of the predominant histological types of carcinoma but also those of co-existing types, especially in cases of "tubular differentiation--well, mucus in cytoplasm--poor."

[Resection of lung cancer complicated by pleural empyema]

In a 53-year-old man, carcinoma of the lung was resected and was complicated by pleural empyema. Two days after fiberoptic bronchoscopy, he developed a high fever and was found to have pleural empyema. After thoracic drainage and other palliative treatment, the right lower lobe and empyema cavity were resected. The postoperative course was uneventful and he was discharged 3 weeks after the operation, but he died of cervical and intrathoracic lymph node recurrence 5 months later. Surgical treatment of malignant lung cancer complicated by pleural empyema has been reported 10 times, including 3 reports from Japan. According to those reports, post-operative complications are rare, and long survival is possible. Therefore, surgical resection is indicated in some cases.

Solubilization of glycosyl-phosphatidylinositol-anchored proteins in quiescent and stimulated neutrophils

In human neutrophils, alkaline phosphatase (AlkPase), a low-affinity receptor for IgG (FcRIIIB), and complement decay accelerating factor (DAF) are glycosyl-phosphatidylinositol (GPI)-anchored proteins. Varying greatly in biological function these three integral membrane proteins exhibit regulated cell surface expression in neutrophils. Defined by their common membrane-linkage motif, AlkPase, FcRIIIB, and DAF can be released from the lipid bilayer by the action of phosphatidylinositol-specific phospholipase C and are relatively resistant to low temperature extraction with Triton X-100 (TX-100). In this study we show that neutrophil AlkPase, FcRIII, and DAF display differential extractibility; they are relatively insensitive to TX-100 solubilization at 4 degrees C, but are readily extracted with TX-100 at 37 degrees C or by the detergent octyl glucoside at 4 degrees C. The differential extractibility of these GPI-anchored proteins is the same in unstimulated cells, where these proteins exist primarily in an intracellular pool, and stimulated cells, where they are expressed principally at the cell surface. However, no differential extraction effect is observed with two neutrophil transmembrane proteins, complement receptor 1 (CD35, CR1) and MHC Class I in either stimulated or unstimulated cells.

[Cultured human monocytes activated by cytokines or lipopolysaccharide induce fibronectin]

We studied the effects of cytokines such as IL-1 alpha, IL-6 and TNF alpha, and lipopolysaccharide (LPS) on cultured human monocytes. Increased fibronectin (FN) production, as a indicator of the activation of monocytes, was observed with any cytokines or LPS stimulation those were added in the culture medium. These increased FN production by cytokines showed a dose dependent fashion, and 4 hours culture with these cytokines was enough to obtain the amount of FN measured with radioimmunoassay. The combination of sub-optimal dose of cytokines (IL-1 alpha + IL-6, IL-1 alpha, IL-6 + TNF alpha), that could not induce substantial amount of FN with any single cytokine, also could induce FN by cultured monocytes. The specificity of cytokines for the FN production by cultured monocytes was confirmed by the neutralization using monoclonal antibodies specific for each monokines. Northern blot analysis with cDNA specific for FN confirmed the expression of FN mRNA in cultured monocytes stimulated with cytokines or LPS. Cytokine network plays an essential role for immune and inflammatory reaction, and FN has been shown to induce monokines through VLA-5 receptor on cultured monocytes. Our data suggests that monocytes may not always require high concentration of cytokines for the activation of monocytes in vitro, and that the synergistic action of low concentration of cytokines for the activation was enough for the progression of immune or inflammatory reaction.

Targetability of novel immunoliposomes modified with amphipathic poly(ethylene glycol)s conjugated at their distal terminals to monoclonal antibodies

Distearoyl-N-(3-carboxypropionoyl poly(ethylene glycol) succinyl)phosphatidylethanolamine (DSPE-PEG-COOH) was newly synthesized and used to prepare novel immunoliposomes carrying monoclonal antibodies at the distal ends of the PEG chains (Type C). Liposomes were prepared from egg phosphatidylcholine (ePC) and cholesterol (CH) (2;1, m/m) containing 6 mol% of DSPE-PEG-COOH, and a monoclonal IgG antibody, 34A, which is highly specific to pulmonary endothelial cells, was conjugated to the carboxyl groups of DSPE-PEG-COOH to give various amounts of antibody molecules per liposome. Other immunoliposomes with PEG coating (Type B) or without PEG coating (an earlier type of immunoliposome, Type A) were prepared for comparison. The average molecular weight of PEG in Type B or C immunoliposomes was 2000. Type B and Type C liposomes without antibodies showed prolonged circulation time and reduced reticulo-endothelial system (RES) uptake owing to the presence of PEG. These three different types of 34A-immunoliposomes with 30-35 antibody molecules per vesicle were injected into mice to test the immunotargetability to the lung. The efficiency of lung binding of 34A-Type B was one-half of that of 34A-Type A, though a large amount of 34A-Type B remained in the blood circulation for a long time, suggesting that the steric hindrance of PEG chains reduced not only the immunospecific antibody-antigen binding, but also the RES uptake. The degree of lung binding of 34A-Type C was about 1.3-fold higher than that of 34A-Type A, indicating that recognition by the antibodies attached to the PEG terminal was not sterically hindered and that the free PEG (i.e., that not carrying antibody) was effective in increasing the blood concentration of immunoliposomes by enabling them to evade RES uptake. The latter phenomenon was confirmed by using nonspecific antibody-Type C immunoliposomes (14-Type C), which showed a high blood level for a long time. Our approach provides a simple means of conjugating antibodies directly to the distal end of PEG which is already bound to the liposome membrane, and should contribute to the development of superior targetable drug delivery vehicles for use in diagnostics and therapy.

Dilating effect of prostaglandin on the constricted ductus arteriosus in newborn rats

The dilating effect of prostaglandin (PG) E1 and E2 on the once-constricted ductus arteriosus (DA) was examined in newborn rats. The animals were given subcutaneously PGs 3hr after caesarean delivery. The ratio of the DA to the pulmonary artery (PA) was determined 15, 30, 60, 90 and 180 min after injection. Both PGE1 and PGE2 dilated the DA for over 90 min. The maximal effect appeared 15 or 30 min after injection. The DA/PA ratio was significantly higher in PGE2 than in PGE1. In addition, another series of newborn rats were given subcutaneously PGE2 6 hr after caesarean delivery to examine the age-related changes in the DA-dilating effect. The DA/PA ratio was significantly decreased in 6-hr-old pups than in 3-hr-old pups. These findings indicate that both PGE1 and PGE2 have a dilating effect on the once-constricted DA and that the effect decreases with time.

Use of 1.4-nm immunogold particles for immunocytochemistry on ultra-thin cryosections

We present a new application for the use of small immunogold particles (approximately 1.4-nm diameter) for ultrastructural immunocytochemistry. These small gold particles have been used on ultra-thin cryosections in conjunction with a silver enhancement procedure that does not degrade ultrastructural detail. We have used the human neutrophil as a model system, in which known protein markers of two different cytoplasmic granules were localized, in the development of this procedure. The 1.4-nm immunogold particles coupled with silver enhancement yield intense labeling for localization of lactoferrin, a marker for the specific granules, and myeloperoxidase, a marker for the azurophil granules. Double labeling in which one antigen was visualized with 1.4-nm gold and silver enhancement and a second antigen was detected with colloidal gold-IgG on the same ultra-thin cryosection was successfully achieved. We also show that 1.4-nm diameter immunogold particles penetrate into cryosectioned neutrophils to a greater extent than 5-nm or 10-nm immunogold probes. These results show that small immunogold particles, along with silver enhancement, are a useful addition to the immunolabeling methods available for use with ultra-thin cryosections.

Pharmacokinetics and pharmacodynamics of the alpha 1-adrenergic antagonist bunazosin retard in hypertensives

The pharmacokinetics and pharmacodynamics of an alpha 1-blocker a sustained release formulation of bunazosin (Detantol R, E1015, 4-amino-2-(4-butyrylhexahydro-1H-1,4-diazepin-1-yl)-6,7- dimethoxyquinazoline hydrochloride, CAS 52712-76-2), were investigated in hypertensive patients with normal renal function (NRF) and those with impaired renal function (IRF). The subjects were hospitalized and placed on a constant sodium diet (NaCl 7 g/day) throughout the study. A 6 mg dose of bunazosin was administered orally once a day for 8 days. Measurement of blood pressure (BP) and sampling of blood and urine specimens were made on the first and last days of treatment. A significant decrease in both systolic and diastolic BP was observed after consecutive dosing of bunazosin compared to baseline values over 24 h in the NRF and for 8 h in the IRF. There were no significant differences in plasma profiles of bunazosin in both groups after single and consecutive dosing. The pharmakokinetic parameters of bunazosin in the NRF and IRF groups did not differ after the single and the consecutive dosing, except for plasma peak levels (Cmax) which were significantly higher in the IRF than those in the NRF. There were, however, neither prolongation of apparent elimination half-life (t1/2), nor increase in Cmax, nor area under the plasma concentration-time curve (AUC0-24) after consecutive dosing in both groups. Cumulative urinary excretion rates of bunazosin were less than 1.1% of dose in both groups, and those did not differ significantly between the NRF and IRF groups in both single and consecutive studies.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of hypertension and aging on fibronectin expression in aorta of Dahl salt-sensitive rats

Effects of hypertension and aging on aortic fibronectin expression were investigated in male Dahl salt-sensitive (Dahl-S) and salt-resistant (Dahl-R) rats fed either a low- or high-salt diet from 5 to 37 wk of age. In comparison to low-salt controls, the steady-state mRNA levels for aortic fibronectin in salt-loaded Dahl-S rats were dramatically increased at 37 wk of age, corresponding to a severe stage of hypertension with high mortality, whereas at earlier ages representing early to established phases of hypertension, no significant changes were observed. Salt loading affected neither blood pressure nor aortic fibronectin expression in Dahl-R rats. Aging without coexisting hypertension did not cause significant changes in aortic fibronectin mRNA levels all through the study period in either strain of rats. These results suggest that aortic fibronectin may be strongly regulated by factors associated with severe hypertensive organ damages caused by long-standing hypertension in salt-loaded Dahl-S rats. Also suggested was that aortic fibronectin may not play a major role in the pathogenesis of early aortic changes occurring in response to hypertension or as a process of aging.

[A case of squamous cell carcinoma of negative tumor shadow arising from pulmonary cyst]

We report a case of 53-year-old man who performed resection of infected cystic lung lesion seen from his childhood. Chest X-ray showed no remarkable change in the wall of the cyst, and tumor shadow was negative. As the chest cavity was severely adhesive, operation was ended in partial resection including the cyst. Pathological study revealed moderately differentiated squamous cell carcinoma replacing the entire cystic wall. Right upper lobectomy and dissection of lymph nodes were performed as second operation. Microscopically, carcinoma was limited in the wall of the cyst.

Microsatellite instability in the progression of gastric carcinoma

Seventy-six gastric carcinomas were analyzed with regard to whether or how microsatellite instability was associated with the development of the carcinoma. Microsatellite instability occurred as a late genetic alteration, with an incidence significantly higher in the advanced stage (17 of 51) than in the early stage (3 of 25; P < 0.05). Chromosomal losses on 5q and 17p, detected by polymerase chain reaction-restriction fragment length polymorphism, more frequently accompanied microsatellite instability (9 of 15 and 8 of 11, respectively), compared with carcinomas which lacked instability (5 of 28 and 9 of 30, respectively; P < 0.01 and P < 0.05, respectively). Epstein-Barr virus was observed in only 8 of 76 carcinomas, none of which was associated with microsatellite instability. No significant correlation was found between instability and the familial tendency to develop gastric carcinomas. Our results suggest that microsatellite instability might play a role in the progression of gastric carcinomas but not in Epstein-Barr virus-associated gastric carcinomas.

Differential expression of bcl-2 and susceptibility to anti-Fas-mediated cell death in peripheral blood lymphocytes, monocytes, and neutrophils

The recently identified Fas antigen (Ag) is a cell surface molecule that can mediate apoptosis. The cytoplasmic product of proto-oncogene bcl-2 has been shown to prolong the cellular survival by inhibiting apoptosis. To elucidate the physiologic significance of expression of both molecules, we examined the expression of Fas Ag and bcl-2 on blood leukocyte populations and evaluated their sensitivity to the cytolytic action of anti-Fas antibody. Although Fas Ag was expressed on a fraction of lymphocytes, both neutrophils and monocytes expressed Fas Ag constitutively. In contrast, there was marked difference among these leukocytes regarding bcl-2 expression. Lymphocytes expressed bcl-2 intensely, but monocytes showed weaker bcl-2 expression, and neutrophils were essentially absent for bcl-2 expression. Seemingly reflecting this lack of bcl-2-expression, neutrophils more easily underwent apoptotic cell death in vitro as compared with monocytes and lymphocytes. We showed that anti-Fas antibody affectively accelerated apoptotic cell death in neutrophils. However, the apoptosis-inducing effect of anti-Fas antibody was minimal on monocytes, and lymphocytes were resistant to this antibody. These results suggest that anti-Fas-mediated cell death may, in part, be determined by bcl-2 expression status in Fas+ lymphoid and hematopoietic cells.