Mechanisms of lymphocyte adhesion to cultured human corneal epithelial cells

PURPOSE

The authors studied the adhesion mechanisms between peripheral blood lymphocytes (PBL) and cultured human corneal epithelial (HCE) cells to investigate the lymphocyte interaction with corneal epithelial cells in the corneal immune response.

METHODS

First, the authors examined the expression of intercellular adhesion molecule (ICAM)-1 or lymphocyte function-associated antigen (LFA)-3 on the normal human corneal epithelium and cultured HCE cells by an immunostaining technique and flow cytometry. Effects of inflammatory cytokines such as interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha, on ICAM-1 or LFA-3 expression on cultured HCE cells were also examined. Second, the authors performed an adhesion assay with 51Cr-labeled monocyte-depleted PBL from normal, healthy volunteers and cultured HCE cells, with and without treatment of IFN-gamma or TNF-alpha in 96-well-plates for 1 hour at 37 degrees C in 5% CO2. After unbound PBL were removed, the radioactivity of the sample in each well was counted with a scintillation counter. In addition, the authors evaluated the blocking effects of monoclonal antibodies (mAbs) on the adhesion of PBL to the cultured HCE cells.

RESULTS

ICAM-1 expression was not detected in the normal human corneal epithelium. However, the expression of ICAM-1 was detected on the cultured HCE cells with Dulbecco's Modified Eagle Medium supplemented with 10% fetal bovine serum. In addition, both IFN-gamma and TNF-alpha increased ICAM-1 expression on the cultured HCE cells dramatically. LFA-3 expression was detected in all cell layers of the normal human corneal epithelia. Neither IFN-gamma nor TNF-alpha had any effect on LFA-3 expression on the cultured HCE cells. The PBL adhesion to the HCE cells with and without treatment of IFN-gamma or TNF-alpha was blocked dominantly by anti-ICAM-1 or anti-LFA-1 alpha mAb. Anti-LFA-3 mAb also blocked the PBL adhesion but had less blocking effect than anti-ICAM-1 or anti-LFA-1 alpha mAb. Anti-very late activation antigen beta, or anti-human leukocyte antigen (HLA)-class I or HLA-class II mAb had no effect on the PBL adhesion to the HCE cells. The adhesion percentile of the PBL applied to the HCE cells pretreated with IFN-gamma or TNF-alpha showed a dose-response curve dependent on the concentration of these cytokines.

CONCLUSIONS

The results in the present study demonstrate that (i) adhesion of lymphocytes to HCE cells could be mediated by the LFA-1-ICAM-1 pathway and/or the CD2-LFA-3 pathway; (ii) the LFA-1-ICAM-1 pathway could be crucial in lymphocyte adhesion to HCE cells; (iii) IFN-gamma or TNF-alpha exerts an enhancing effect not only on the ICAM-1 expression on HCE cells but also on the adhesion of lymphocytes to HCE cells.

An adult case of Cockayne syndrome without sclerotic angiopathy

We report an autopsy case of Cockayne syndrome (CS). A 40-year-old Japanese woman was admitted to our hospital for cachexia. She had displayed the striking features of CS, including dwarfism, mental retardation, neural deafness, ataxia, intracranial calcifications, and progeria since her childhood. Endocrinological examinations suggested normal pituitary function and a disorder of the hypothalamus or the cerebrum. She died of acute pneumonia at the age of 42. Autopsy findings showed typical abnormalities in the central nervous system compatible with CS; however, no atherosclerotic change was observed in the systemic arteries.

[Three cases of thymic hyperplasia associated with hyperthyroidism]

We encountered three cases of thymic hyperplasia associated with hyperthyroidism. Case 1 was in a 35-year-old woman; a chest CT scan showed an anterior mediastinal mass and right-sided pleural effusion, which suggested the presence of a thymoma Case 2 was in a 21-year-old man who complained of palpebral ptosis and also had myasthenia gravis (Osserman type I). Case 3 was in a 47-year-old woman; a chest CT scan showed thymic hyperplasia and mediastinal lymphadenopathy. In all cases, anti-thyroid medication was given first, because of the associations with hyperthyroidism. Moreover, in cases 1 and 2 no tumor was found, and only hyperplasia was detected in the thymus, although both patients underwent extended thymectomy. Furthermore, surgery was not effective against the hyperthyroidism (anti-thyroid medication could not be withdrawn or reduced). In cases 2 and 3, thymic hyperplasia, as seen on chest CT scans, resolved as thyroid function was normalized by anti-thyroid medication. The pretracheal lymphadenopathy seen in case 3 also resolved. Thymic hyperplasia may have been a result, not a cause, of hyperthyroidism. When we encounter patients with thymic masses and hyperthyroidism, we should give anti-thyroid medication and observe the thymus for some time before resorting to surgery.

[Non-uremic neuropathy in hemodialysis patients]

We have reviewed 20 clinical records of hemodialysis patients with neuropathy admitted to the Department of Neurology during 1978 april through 1995 march. The clinical diagnosis was made based on clinical findings, neurophysiological examinations, and histopathological findings of sural nerve and peroneal muscle biopsies. Four out of twenty hemodialysis patients with neuropathy were non-uremic neuropathy. The diagnosis of neuropathy of four patients were chronic inflammatory demyelinating polyneuropathy, neuropathy with graft versus host disease, Guillain-Barré syndrome, and subacute combined degeneration of the spinal cord. All patients improved after the treatment. It is important to consider the possibility of association of non-uremic neuropathy in hemodialysis patients.

Altered ceramide and sphingosine expression during the induction phase of ischemic acute renal failure

Recent evidence indicates that a "sphingomyelin signaling pathway" exists: in response to heterogeneous influences, sphingomyelin is hydrolyzed, liberating ceramide, and subsequently its sphingoid base, sphingosine. Ceramide and sphingosine can influence diverse cellular processes, including cell differentiation, proliferation, protein trafficking, and apoptosis. Each of these processes have important implications for post-ischemic acute renal failure (ARF). However, sphingosine and ceramide expression during the induction of ischemic/reperfusion injury have not been previously assessed. To this end, CD-1 mice were subjected to 45 minutes of unilateral renal ischemia +/- reperfusion, followed by cortical sphingosine, ceramide, and sphingomyelin assessments. Contralateral kidneys served as controls. Ischemia caused approximately 50% sphingosine and ceramide decrements. During reperfusion, sphingosine rebounded to normal values. Conversely, ceramide rose to, and was maintained at, supranormal levels (approximately 175% of controls). Subsequent studies performed with hypoxic or oxygenated isolated proximal tubules suggested that these changes: (1) had a multifactorial basis; (2) were partially simulated by enhanced PLA2 activity; (3) and were dissociated from alterations in net sphingomyelin content. To assess the potential pathogenic relevance of the documented ceramide increments, cultured human proximal tubule (HK-2) cells were subjected to ATP depletion/Ca2+ ionophore- or PLA2-induced attack with or without exogenous C2 ceramide loading. Ceramide worsened both forms of injury without exerting an independent lethal effect. Conversely, ceramide markedly attenuated arachidonic acid cytotoxicity. This occurred without any decrease in arachidonate uptake, suggesting a direct cytoprotective effect.

IN CONCLUSION

(1) sphingosine and ceramide fluxes are hallmarks of early ischemic/reperfusion injury; (2) these changes occur via divergent metabolic pathways; and (3) that ceramide increments can affect divergent injury pathways, and that sphingosine and ceramide have potent cell signaling effects, suggest that the currently documented sphingosine/ ceramide fluxes could have important implications for the induction phase and evolution of post-ischemic ARF.

Epigallocatechin gallate-induced histamine release in patients with green tea-induced asthma

BACKGROUND AND OBJECTIVE

Epigallocatechin gallate is the causative agent of green tea-induced asthma. To determine whether an IgE-mediated mechanism plays a pathogenetic role in this disorder, we measured histamine release after in vitro exposure to epigallocatechin gallate.

METHODS

Subjects included eight patients (four men and four women) with green tea-induced asthma, who had been diagnosed by skin test and inhalation challenge, and eight controls (four asthmatic subjects with no previous exposure tea dust and four healthy volunteers). Heparinized whole blood samples were taken and incubated with epigallocatechin gallate at various concentrations (final concentration range, 0.003 to 300 micrograms/mL) for 30 minutes at 37 degrees C. After centrifugation, histamine was measured in the cell-free supernatants by radioimmunoassay. Histamine release was expressed as a percentage of total histamine. A result higher than 10% was considered positive.

RESULTS

In one of the tea-sensitive patients, epigallocatechin gallate did not cause histamine release. Five of the other seven patients (71%) demonstrated a positive, dose-dependent histamine release to epigallocatechin gallate. In asthmatic and normal controls, histamine release was not observed at any epigallocatechin gallate concentration. Furthermore, a significant correlation was noted between the maximum percentage histamine release and the threshold epigallocatechin gallate concentration for intradermal skin testing.

CONCLUSION

These results indicate that an IgE-mediated response is the basis for green tea-induced asthma.

[A case of paradoxical cerebral embolism with 'spectacular shrinking deficit']

A 66-year-old woman was admitted to our hospital because of abrupt onset of left hemiparesis and confusional state. Ten hours prior to admission, she developed difficulty in left hand movement, and her family noticed cloudiness of consciousness and gait disturbance. Neurological examination revealed only a hollow hand sign of the left hand without other neurological deficits. Cranial CT showed a low density area in the right superior parietal region, and the follow up CT on 6th hospital day exhibited contrast enhancement and hemorrhagic transformation in this area. Cerebral angiography demonstrated capillary blush and early venous filling in the right posterior parietal region. Transesophageal color-coded Doppler echocardiography (TEE-CD) showed a shunt flow via patent foramen ovale (PFO). Thus, we diagnosed this case as paradoxical cerebral embolism through PFO, which is characterized by rapid recovery of clinical manifestation, so-called spectacular shrinking deficit. Even in elderly patients with embolic stroke of unknown origin, TEE-CD should be performed to investigate PFO.

Regulation of thymocyte lineage commitment by the level of classical protein kinase C activity

Thymocyte-positive selection involves signaling through TCR and accessory molecules, and the signaling intensity appears to be critical for this event. The specific inhibitor of classical Ca2+-dependent protein kinase C (cPKC), Gö 6976, inhibited positive selection in fetal thymus organ culture, indicating that cPKC activation is essential for positive selection. The major protein kinase C isoforms in CD4+ CD8+ thymocytes are cPKC-alpha, cPKC-beta, and the novel Ca2+-independent protein kinase C, nPKC-epsilon. To analyze the effect of cPKC activation level on positive selection, we used thymocytes from TCR transgenic mice with nonselecting and RAG-2 -/- backgrounds as they were developmentally arrested at the CD4+ CD8+ stage without positive selection signals. These thymocytes survived and acquired CD4/CD8 lineage commitment in suspension culture upon transient stimulation with limited concentrations of the selective activator of cPKC-alpha and -beta, thymeleatoxin, and the calcium ionophore, ionomycin. However, neither 12-deoxyphorbol 13-phenylacetate 20-acetate, which selectively activates cPKC-beta, nor ingenol 3,20-dibenzoate, which selectively activates nPKC-epsilon, exerted such an effect. The thymeleatoxin/ionomycin concentrations corresponded to those that inhibit glucocorticoid-induced apoptosis in thymocytes and were lower than those that induce proliferation of mature T cells. The CD4 lineage commitment required a higher level of cPKC activity than the CD8 lineage commitment. CD8alpha or CD4 mRNA expression was down-regulated. Functional helper and killer T cells were induced from the CD4 and CD8 lineage-committed cells, respectively, by additional stimulation. These results suggest that thymocyte lineage commitment in positive selection is regulated by the level of cPKC-alpha activity or by the levels of cPKC-alpha and -beta activities.

Regulation of thymocyte lineage commitment by the level of classical protein kinase C activity

Thymocyte-positive selection involves signaling through TCR and accessory molecules, and the signaling intensity appears to be critical for this event. The specific inhibitor of classical Ca2+-dependent protein kinase C (cPKC), Gö 6976, inhibited positive selection in fetal thymus organ culture, indicating that cPKC activation is essential for positive selection. The major protein kinase C isoforms in CD4+ CD8+ thymocytes are cPKC-alpha, cPKC-beta, and the novel Ca2+-independent protein kinase C, nPKC-epsilon. To analyze the effect of cPKC activation level on positive selection, we used thymocytes from TCR transgenic mice with nonselecting and RAG-2 -/- backgrounds as they were developmentally arrested at the CD4+ CD8+ stage without positive selection signals. These thymocytes survived and acquired CD4/CD8 lineage commitment in suspension culture upon transient stimulation with limited concentrations of the selective activator of cPKC-alpha and -beta, thymeleatoxin, and the calcium ionophore, ionomycin. However, neither 12-deoxyphorbol 13-phenylacetate 20-acetate, which selectively activates cPKC-beta, nor ingenol 3,20-dibenzoate, which selectively activates nPKC-epsilon, exerted such an effect. The thymeleatoxin/ionomycin concentrations corresponded to those that inhibit glucocorticoid-induced apoptosis in thymocytes and were lower than those that induce proliferation of mature T cells. The CD4 lineage commitment required a higher level of cPKC activity than the CD8 lineage commitment. CD8alpha or CD4 mRNA expression was down-regulated. Functional helper and killer T cells were induced from the CD4 and CD8 lineage-committed cells, respectively, by additional stimulation. These results suggest that thymocyte lineage commitment in positive selection is regulated by the level of cPKC-alpha activity or by the levels of cPKC-alpha and -beta activities.

[Efficacy of nasal bi-level positive airway pressure ventilation in a patient with olivo-ponto-cerebellar atrophy suffering from sleep apnea syndrome]

Sleep apnea with neuromuscular disorders has been successfully treated with bi-level positive airway pressure ventilation (BiPAP), which, unlike continuous positive airway pressure ventilation (CPAP), creates pressure difference between expiratory and inspiratory phases. Hence if the respiration of patients stops longer than a pre-set duration, BiPAP can automatically force them to breath through a nasal mask. We report a 60-year-old woman with olivo-ponto-cerebellar atrophy (OPCA), whose mixed-type sleep apnea was difficult to treat with conventional CPAP. We therefore tried BiPAP on this patient at night. Nocturnal CO2 retention was nearly resolved, and unexpectedly daytime PaCO2 was also corrected with marked improvement of daytime somnolence. BiPAP is totally non-invasive, and may be one of the most effective treatments in patients with OPCA suffering from sleep apnea.

[Prophylactic effect of black tea extract as gargle against influenza]

We examined whether gargling with black tea prevents influenza infection. Tests were carried out during a five month period (October 1992 to March 1993). The control group that followed their normal daily routine, whereas the test group that gargled with 0.5 w/v% black tea extract twice daily (at 8 a.m. and 5 p.m.). Influenza viruses were isolated from influenza patients and an antigen analysis was carried out. As a result, two strains of influenza A viruses (H3N2) and ten strains of B virus were detected. An HI test was done using paired sera of the control group and the test group. The HI titers raised a four fold or greater in 48.8% (61/125) in the control group and 35.1% (35/134) in the test group. There was a significant difference (p < 0.05) between the control and test groups. These results indicate that black tea extract is effective as a prophylactic agent against influenza infection.

[A case of basilar artery occlusion associated with one-and-a-half syndrome, paralytic pontine exotropia and WEBINO-syndrome]

We report a 79-year-old woman with basilar artery occlusion. She had a sudden onset of tetraplegia and disturbed consciousness, and within four days from the onset she showed a varied, fluctuating eye symptoms. On admission, she showed ocular bobbing, skew deviation with the right eye lower-positioned, upward gaze palsy, one-and-a-half syndrome, and paralytic pontine exotropia (PPE). On the third day after the onset, she showed wall-eyed bilateral internuclear ophthalmoplegia (WEBINO) syndrome, and on the fourth day, she showed one-and-a-half syndrome again. Her right-gaze palsy improved repeatedly, and on the 19th day from the onset, only right MLF syndrome remained. Her eye symptoms fluctuated probably according to the distal migration of emboli, there by the responsible lesion and the mechanism of these eye symptoms are considered to be closely inter-correlated. On the fourth day after onset, the magnetic resonance imaging revealed cerebral infarctions in bilateral middle pons, the left paramedian lower pons, and the right paramedian midbrain, and a hemorrhagic infarction in the right inferior cerebellar hemisphere. We believe that that the eye symptoms of this patient were caused by lesions in the paramedian midbrain or pons.

El Tor hemolysin of Vibrio cholerae O1 forms channels in planar lipid bilayer membranes

We investigated the channel formation by El Tor hemolysin (molecular mass, 65 kDa) of Vibrio cholerae O1 biotype El Tor in planar lipid bilayers. The El Tor hemolysin channel exhibited asymmetric and hyperbolic membrane current with increasing membrane potential, meaning that the channel is voltage dependent. The zero-current membrane potential measured in KCI solution showed that permeability ratio PK+/PCl- was 0.16, indicating that the channel is 6-fold more anion selective over cation. The hemolysin channel frequently flickered in the presence of divalent cations, suggesting that the channel spontaneously opens and closes. These data imply that the El Tor hemolysin damages target cells by the formation of transmembrane channels and, consequently, is the cause of osmotic cytolysis.

Development of a time-resolved fluoroimmunoassay (TR-FIA) for testosterone: measurement of serum testosterone concentrations after testosterone treatment in the rainbow trout (Oncorhynchus mykiss)

A sensitive time-resolved fluoroimmunoassay (TR-FIA) for testosterone was developed, and the assay system was used for measuring serum testosterone concentrations in rainbow trout. Testosterone-3-(O-carboxymethyl)oxime-bovine serum albumin (T-3-CMO-BSA) was immobilized by physical adsorption to the wells of microtiter plates. A competitive assay using two antibodies was performed among T-3-CMO-BSA in the solid-phase, unknown amounts of testosterone, testosterone antibodies, and europium labeled secondary antibodies, followed by measurements using a time-resolved fluorometer (DELFIA system). The TR-FIA had a sensitivity of 0.075 pg/50 microliters sample (1.5 pg/ml), and the range of the assay system was between 1.5 pg/ml and 25 ng/ml. The intra- and interassay coefficients of variation for the testosterone TR-FIA were satisfactorily low, and were between 1.62 and 6.38% and 2.96 and 8.29%, respectively. The assay system was applied to measure the serum testosterone concentrations after an injection of testosterone dissolved in saline, propyleneglycol, or coconut oil. Among the three solvents, the coconut oil group showed continuously high serum testosterone level. In contrast, the saline and propyleneglycol groups had maximum concentrations 24 hr after the injection, but their levels were significantly lower than that of the coconut oil group. The testosterone TR-FIA method is sensitive, repeatable, and is as accurate as conventional RIAs. It is very good for measuring serum testosterone concentrations.

A de novo recombination in the ABO blood group gene and evidence for the occurence of recombination products

We have encountered a paternity case where exclusion of the putative father was only observed in the ABO blood group (mother, B; child, A1; putative father, O), among the many polymorphic markers tested, including DNA fingerprints and microsatellite markers. Cloning a part of the ABO gene, PCR-amplified from the trio's genomes, followed by sequencing the cloned fragments, showed that one allele of the child had a hybrid nature, comprising exon 6 of the B allele and exon 7 of the O1 allele. Based on the evidence that exon 7 is crucial for the sugar-nucleotide specificity of A1 and B transferases and that the O1 allele is only specified by the 261G deletion in exon 6 of the consensus sequence of the A1 allele, we concluded that the hybrid allele encodes a transferase with A1 specificity, resulting, presumably, from de novo recombination between the B and O1 alleles of the mother during meiosis. Screening of random populations demonstrated the occurrence of four other hybrid alleles. Sequencing of intron VI from the five hybrid alleles showed that the junctions of the hybrid alleles were located within intron VI, the intron VI-exon 7 boundaries, or exon 7. Recombinational events seem to be partly involved in the genesis of sequence diversities of the ABO gene.

Marinesco-Sjögren syndrome associated with acute myeloblastic leukemia

Marinesco-Sjögren syndrome is a rare autosomal recessive disorder characterized by cerebellar atrophy, ataxia, cataracts, short stature and varying degrees of mental retardation. A high incidence of malignant disease associated with this syndrome has not so far been reported. We report the case of a 6-year-old girl affected with Marinesco-Sjögren syndrome, who developed acute myeloblastic leukemia (AML, M2), and whose karyotype was 46,XX,t(8;21),(q22;q22) in bone marrow blasts. This is the first report of Marinesco-Sjögren syndrome associated with malignant disorders.

A study of bronchus-associated lymphoid tissue in a rat model of chronic pulmonary infection with Pseudomonas aeruginosa

The immunologic pathogenesis of conditions characterized by chronic pulmonary infections, such as diffuse panbronchiolitis and those associated with cystic fibrosis, had not been fully clarified. Organized lymphoid tissue along the airway has been termed bronchus-associated lymphoid tissue (BALT), and hyperplasia of BALT is frequently observed in chronic pulmonary infections in humans. To investigate the role of BALT, we intratracheally inoculated rats with Pseudomonas aeruginosa (PA) enmeshed in agar beads according to the method of Cash et al., thereby establishing a chronic pulmonary infection model. Histopathological examination of tissue from this rat model revealed the accumulation of lymphocytes and foamy cells around bronchioles. This finding corresponds to chronic bronchiolitis in humans. Hyperplasia of BALT was also observed. Immunohistochemical examination demonstrated that Ia+ cells, helper T cells, surface IgM-positive (sIgM+) cells and sIgA+ cells had gradually increased in BALT and the walls of peripheral airways during the period from day 4 to 7. The anti-PA IgA antibody titer in bronchoalveolar lavage fluid (BALF) was also elevated during this period. After day 21, non-helper T cells became predominant in tissue sections, and the numbers of various immunoglobulin-positive cells as well as the anti-PA IgA antibody titer in BALF were reduced. Histological examination revealed that the inflammatory findings had also diminished. The time course of changes in the various immune cells in BALT and the walls of peripheral airways, paralleled the reductions in anti-PA IgA antibody titers in BALF. Our findings suggest that hyperplastic BALT may be one source of the Ig producing cells which play an important role in the local immune response characteristic of chronic pulmonary infections.

[Clinicopathological features of interstitial pneumonia associated with amyopathic dermatomyositis]

We studied clinicopathological characteristics of interstitial pneumonia associated with amyopathic dermatomyositis. The subjects comprised two men and three women, and their mean age was 58.2 years. All subjects had cruptions specific for dermatomyositis, but had no signs of myositis. They all presented with acutely or subacutely developed coughing and dyspnea. Results of tests for anti-Jo-1 antibody were negative in all cases. Chest X-ray films showed infiltrations or streaky shadows, or both in the middle and lower lung fields. Analysis of bronchoalveolar lavage fluid revealed abnormally high percentages of lymphocytes and neutrophils. In one patients a specimen obtained by open lung biopsy showed homogeneous cell infiltrations in alveolar septa and regional alveolar damage. That patient was successfully treated with cyclosporin and corticosteroids in early phase of the disease. The other four patients received immunosuppressive agents after respiratory failure developed. All four died despite having received high-dose corticosteroid and immunosuppressive therapy. Examination of autopsy specimens showed diffuse alveolar damage.

Pattern reversal visual evoked potentials in classic and common migraine

Pattern reversal visual evoked potentials (PVEPs) to transient checkerboard were recorded in 19 patients with migraine with visual aura (i.e., classic migraine), 14 patients with migraine without aura (i.e., common migraine) in the interictal period and 43 normal subjects. Latencies and amplitudes of PVEPs in each group were analyzed. In classic migraine patients, P100 amplitude was significantly higher than in normal subjects (p < 0.01), whereas latencies of PVEPs did not significantly differ. There were no significant differences between the common migraine and normal subjects, nor within the classic and common migraine groups in latencies and amplitudes of PVEP. Four patients with classic migraine underwent PVEPs during or 1-2 h immediately after their migraine attacks. Two of these patients who underwent PVEPs 1.5-2 h after their attacks showed abnormally increased PVEP amplitudes. These results suggest that there are different pathophysiologies in the visual pathway between classic and common migraine and furthermore, classic migraine patients in interictal periods may have hyperexcitability in the visual pathway and that the increased amplitude of PVEPs after attacks may be due to cortical spreading depression.

Inorganic fluoride. Divergent effects on human proximal tubular cell viability

Fluoride (F) is a widely distributed nephrotoxin with exposure potentially resulting from environmental pollution and from fluorinated anesthetic use (eg, isoflurane). This study sought to characterize some of the subcellular determinants of fluoride cytotoxicity and to determine whether subtoxic F exposure affects tubular cell vulnerability to superimposed ATP depletion and nephrotoxic attack. Human proximal tubular cells (HK-2) were cultured with differing amounts of NaF (0 to 20 mmol/L, overlapping with clinically relevant intrarenal/urinary levels after fluorinated anesthetic use). After completing 24-hour exposures, cell injury was determined (vital dye uptake). Fluoride effects on cell deacylation ([3]H-C20:4 release) and PLA2 activity were also assessed. To determine whether subtoxic F exposure alters tubular cell susceptibility to superimposed injury, cells were exposed to subtoxic NaF doses for 0 to 24 hours and then challenged with simulated ischemia (ATP depletion plus Ca2+ overload) or a clinically relevant nephrotoxic insult (myoglobin exposure). NaF induced dose-dependent cytotoxicity (up to approximately 90% vital dye uptake and increased [3H]C20:4 release). Extracellular Ca2+ chelation (EGTA) and PLA2 inhibitor therapy (aristolochic acid, dibucaine, or mepacrine) each conferred significant protective effects. When subtoxic NaF doses were applied, partial cytosolic PLA2 depletion rapidly developed (approximately 85% within 3 hours, determined on cell extracts). These partially PLA2-depleted cells were markedly resistant to ATP depletion/Ca2+ ionophore injury and to myoglobin-induced attack (approximately 50% decrease in cell death). We conclude that 1) F induces dose-dependent cytotoxicity in cultured human proximal tubular cells, 2) this occurs, in part, via Ca(2+)- and PLA2-dependent mechanism(s), 3) partial cytosolic PLA2 depletion subsequently results, and 4) subtoxic fluoride exposure can acutely increase cell resistance to further attack. Reductions in cytosolic PLA2 activity could potentially contribute to this result.