Calcium and inositolphosphates in the activation of T cell-mediated cytotoxicity

Low perforin expression of early differentiated HCV-specific CD8+ T cells limits their hepatotoxic potential

BACKGROUND & AIMS

Perforin plays a central role in the immunopathogenesis of different viral infections. However, its role in hepatitis C virus (HCV) infection has not been fully understood. Here, we analyzed two closely related questions: first, is CD8+ T cell-mediated killing of HCV-replicating human hepatoma cells mediated by perforin? Second, if so, do HCV-specific CD8+ T cells obtained from chronically HCV infected patients express and upregulate perforin?

METHODS

Susceptibility of HCV-replicating human hepatoma cells to the cytotoxic pathway was tested in vitro by addition of perforin substitute streptolysin O and granzyme B and by co-culture experiments with a perforin-expressing HCV-specific CD8+ T cell clone in the presence of perforin or caspase inhibitors. HCV-specific CD8+ T cells were obtained and analyzed for perforin expression and differentiation markers ex vivo from 12 chronically infected patients and 12 patients with resolved HCV infection.

RESULTS

HCV-replicating human hepatoma cells were susceptible to cytotoxic killing in vitro and a dominant role of perforin in HCV-specific CD8+ T cell-mediated cytolysis was observed. However, HCV-specific CD8+ T cells obtained ex vivo from chronically HCV infected patients expressed only low levels of perforin and showed an impaired ability to upregulate perforin. This was tightly linked to the distinct differentiation stage of HCV-specific CD8+ T cell differentiation ex vivo since early and intermediate differentiated HCV-specific CD8+ T cells only showed weak perforin expression in contrast to late differentiated CD8+ T cells that displayed strong perforin expression.

CONCLUSIONS

Our results suggest that perforin plays a dominant role in CD8+ T cell-mediated lysis of HCV-replicating human hepatoma cells but that lysis may be limited in human chronic viral infection by the low perforin expression of early/intermediate differentiated HCV-specific CD8+ T cells.

Ca2+ release from the endoplasmic reticulum of NY-ESO-1-specific T cells is modulated by the affinity of TCR and by the use of the CD8 coreceptor

Although several cancer immunotherapy strategies are based on the use of analog peptides and on the modulation of the TCR affinity of adoptively transferred T cells, it remains unclear whether tumor-specific T cell activation by strong and weak TCR stimuli evoke different Ca(2+) signatures from the Ca(2+) intracellular stores and whether the amplitude of Ca(2+) release from the endoplasmic reticulum (ER) can be further modulated by coreceptor binding to peptide/MHC. In this study, we combined functional, structural, and kinetic measurements to correlate the intensity of Ca(2+) signals triggered by the stimulation of the 1G4 T cell clone specific to the tumor epitope NY-ESO-1(157-165). Two analogs of the NY-ESO-1(157-165) peptide, having similar affinity to HLA-A2 molecules, but a 6-fold difference in binding affinity for the 1G4 TCR, resulted in different Ca(2+) signals and T cell activation. 1G4 stimulation by the stronger stimulus emptied the ER of stored Ca(2+), even in the absence of CD8 binding, resulting in sustained Ca(2+) influx. In contrast, the weaker stimulus induced only partial emptying of stored Ca(2+), resulting in significantly diminished and oscillatory Ca(2+) signals, which were enhanced by CD8 binding. Our data define the range of TCR/peptide MHC affinities required to induce depletion of Ca(2+) from intracellular stores and provide insights into the ability of T cells to tailor the use of the CD8 coreceptor to enhance Ca(2+) release from the ER. This, in turn, modulates Ca(2+) influx from the extracellular environment, ultimately controlling T cell activation.

Calcium influx and signaling in cytotoxic T-lymphocyte lytic granule exocytosis

Cytotoxic T lymphocytes (CTLs) kill targets by releasing cytotoxic agents from lytic granules. Killing is a multi-step process. The CTL adheres to a target, allowing its T-cell receptors to recognize antigen. This triggers a signal transduction cascade that leads to the polarization of the microtubule cytoskeleton and granules towards the target, followed by exocytosis that occurs specifically at the site of contact. As with cytokine production by helper T cells (Th cells), target cell killing is absolutely dependent on Ca2+ influx, which is involved in regulating both reorientation and release. Current evidence suggests that Ca2+ influx in CTLs, as in Th cells, occurs via depletion-activated channels. The molecules that couple increases in Ca2+ to reorientation are unknown. The Ca2+/calmodulin-dependent phosphatase calcineurin, which plays a critical role in cytokine production by Th cells, is also involved in lytic granule exocytosis, although the relevant substrates remain to be identified and calcineurin activation is only one Ca2+-dependent step involved. There are thus striking similarities and important differences between Ca2+ signals in Th cells and CTLs, illustrating how cells can use similar signal transduction pathways to generate different functional outcomes.

Antisense-mediated loss of calcium homoeostasis endoplasmic reticulum protein (CHERP; ERPROT213-21) impairs Ca2+ mobilization, nuclear factor of activated T-cells (NFAT) activation and cell proliferation in Jurkat T-lymphocytes

We recently discovered a novel gene on chromosome 19p13.1 and its product, an integral endoplasmic reticulum (ER) membrane protein, termed CHERP (calcium homoeostasis endoplasmic reticulum protein). A monoclonal antibody against its C-terminal domain inhibits Ins(1,4,5) P (3)-induced Ca(2+) release from ER membrane vesicles of many cell types, and an antisense-mediated knockdown of CHERP in human erythroleukemia (HEL) cells greatly impaired Ca(2+) mobilization by thrombin. In the present paper, we explore further CHERP's function in Jurkat T-lymphocytes. Confocal laser immunofluorescence microscopy showed that CHERP was co-localized with the Ins(1,4,5) P (3) receptor throughout the cytoplasmic and perinuclear region, as previously found in HEL cells. Transfection of Jurkat cells with a lac I-regulated mammalian expression vector containing CHERP antisense cDNA caused a knockdown of CHERP and impaired the rise of cytoplasmic Ca(2+) (measured by fura-2 acetoxymethyl ester fluorescence) caused by phytohaemagglutinin (PHA) and thrombin. A 50% fall of CHERP decreased the PHA-induced rise of the cytoplasmic free Ca(2+) concentration ([Ca(2+)](i)), but Ca(2+) influx was unaffected. Greater depletion of CHERP (>70%) did not affect the concentration of Ins(1,4,5) P (3) receptors, but diminished the rise of [Ca(2+)](i) in response to PHA to </=30% of that in control cells, decreased Ca(2+) influx and slowed the initial rate of [Ca(2+)](i) rise caused by thapsigargin, an inhibitor of the sarcoplasmic/endoplasmic-reticulum Ca(2+)-ATPase, suggesting there was also some deficit in ER Ca(2+) stores. In CHERP-depleted cells the Ca(2+)-dependent activation and translocation of the key transcription factor NFAT (nuclear factor of activated T-cells) from cytoplasm to nucleus was suppressed. Furthermore, cell proliferation was greatly slowed (as in HEL cells) along with a 60% decrease in cyclin D1, a key regulator of progression through the G(1) phase of the cell cycle. These findings provide further evidence that CHERP is an important component of the ER Ca(2+)-mobilizing system in cells, and its loss impairs Ca(2+)-dependent biochemical pathways and progression through the cell cycle.

Functional importance and caffeine sensitivity of ryanodine receptors in primary lymphocytes

Calcium signaling patterns are important for the specific regulation of activation and effector function in lymphocytes. Studies of [Ca2+]i regulation in lymphocytes, including the involvement of ryanodine receptors (RyR) and the importance of caffeine-sensitive pools, have been carried out mainly in lymphocyte cell lines and the presence and functional importance of these pools in primary lymphocytes has not been addressed. Here we show by confocal microscopy that caffeine caused a prompt but transitory increase of [Ca2+]i in primary lymphocytes, an effect that was inhibited by pre-treatment with ryanodine. Furthermore, the increase of [Ca2+]i in CD4+ and CD8+ MLR T lymphocytes stimulated by 5 microg/ml concanavalin A was significantly inhibited by pretreatment with caffeine. In functional studies, caffeine decreased cytotoxicity against myocyte target cells which is probably related to an altered calcium signaling in CD8+ MLR lymphocytes. Caffeine also terminated spontaneous Ca2+ oscillations and induced a rise in [Ca2+]i in CD4- and CD8- MLR lymphocytes probably of B cell origin. These results demonstrate that caffeine alters Ca2+ signaling in primary lymphocytes, and suggest that RyR, probably the skeletal muscle receptor (RyR-1) and brain receptor (RyR-3), are involved in mediating this effect. It is also possible that blocking of inositol-1,4,5-triphosphate (IP3) receptors is involved in the effects of caffeine on lymphocyte activation.

Expression of purinergic receptors (ionotropic P2X1-7 and metabotropic P2Y1-11) during myeloid differentiation of HL60 cells

The expression of human purinergic P2 receptors (P2X1-7 and P2Y1-11) as well as the ecto-enzymes apyrase (CD39) and 5'-nucleotidase (CD73) was investigated on the nucleic acid level during granulocytic and monocytic differentiation of HL60 cells and on peripheral human blood leukocytes. RT-PCR and dot-blot hybridization assays indicated that mRNA transcripts of all analyzed P2 receptors apart from the P2X3 receptor were expressed during myeloid development of HL60 cells, showing a distinct regulation during the course of differentiation. In blood leukocytes, transcripts of P2X5, P2X7 and all P2Y receptors, except for P2Y6, receptor were found. CD39 and CD73 showed a marked upregulation during myeloid maturation. Functional analysis of P2 receptor-mediated intracellular Ca(2+)-increase after stimulation with ATP revealed no change during granulocytic differentiation, but showed a strong attenuation in both potency and efficacy during monocytic development of HL60 cells.

Human monocyte derived dendritic cells express functional P2X and P2Y receptors as well as ecto-nucleotidases

We investigated the expression and function of P2 receptors and ecto-nucleotidases on human monocyte derived dendritic cells (DC). In addition we analyzed the effect of extracellular ATP on the maturation of DC. By RT-PCR, DC were found to express mRNA for several P2X (P2X1, P2X4, P2X5, P2X7) and P2Y (P2Y1, P2Y2, P2Y4, P2Y5, P2Y6, P2Y10, P2Y11) receptors. As shown by FURA-2 measurement, triggering of P2 receptors resulted in an increase in free intracellular Ca2+. In combination with Tumor necrosis factor-alpha, ATP increased the expression of the DC surface markers CD80, CD83 and CD86 indicating a maturation promoting effect. DC expressed the ecto-apyrase CD39 and the ecto-5'-nucleotidase CD73 as demonstrated by RT-PCR. Extracellular ATP was rapidly hydrolyzed by these ecto-enzymes as shown by separation of 3H-labeled ATP metabolites using a thin layer technique. These data suggest that ATP acts as a costimulatory factor on DC maturation.

Nucleotide metabolizing ectoenzymes are upregulated in A431 cells periodically treated with cytostatic ATP leading to partial resistance without preventing apoptosis

Extracellular ATP, when added as a single dose at concentrations higher than 0.1 mM to the culture medium, was growth inhibitory or even cytotoxic for human epidermoid carcinoma cells (A431). Adenosine at the same concentrations was much less potent. The molecular mechanism underlying the inhibitory effect of extracellular ATP has been investigated. The cytostatic as well as the cytotoxic effects of ATP could be prevented by supplying uridine as a pyrimidine source and, alternatively, by simultaneous addition of dipyridamole, which inhibits the uptake of adenosine. The data suggest that the long-term production and continuous uptake of adenosine, which is enzymatically generated from the ATP in the medium, led to an intracellular nucleotide imbalance with pyrimidine starvation. This triggered suicidal processes ending up in apoptosis of the cells. The tumor cells have been adapted to extracellular ATP with the aim to obtain cells which are more resistant to ATP. Therefore, growing cells were periodically treated with extracellular ATP. These cells were characterized by an enlargement of cell size, a decreased proliferation rate, and a reduced but not abolished sensitivity to cytostatic and cytotoxic ATP doses. The calcium response of adapted cells was shortened. The nucleotide hydrolyzing ectoenzyme activities (ecto-ATPase, ecto-ADPase, ecto-AMPase, ecto-Ap4Aase) were simultaneously upregulated. All phenotypic alterations of the adapted cells disappeared after cultivation for several generations in the absence of extracellular ATP. Considering ATP as a potential chemotherapeutic agent the adaptive phenomena of treated cells might be important.

Oleic acid-induced Ca2+ mobilization in human platelets: is oleic acid an intracellular messenger?

The purpose of this study was to explore the effect of oleic acid (OA) on intracellular Ca2+ mobilization in human platelets. When applied extracellularly, OA produced a concentration dependent rise in cytosolic [Ca2+] ([Ca2+]cyt) when extracellular [Ca2+] (Ca2+]ext) was zero (presence of EGTA), suggesting that OA caused an intracellular release of Ca2+. Intracellular Ca2+ release was directly proportional to entry of OA into platelets and OA entry was indirectly proportional to [Ca2+]ext. In permeabilized platelets, OA caused the release of 45Ca2+ from ATP dependent intracellular stores. Finally, our results show that thrombin stimulated the release of [3H]OA from platelet phospholipids. The saturated fatty acids stearic and palmitic acid did not stimulate an increase in [Ca2+]cyt under these conditions, but the unsaturated fatty acid, linolenic acid produced effects similar to those of OA, suggesting specificity among fatty acids for effects on [Ca2+]cyt. Taken together, our experiments suggest that OA which has been incorporated into platelet phospholipids was released into the cytosol by thrombin stimulation. Our experiments also show that OA stimulates Ca2+ release from intracellular stores. These results support the hypothesis that OA may serve as an intracellular messenger in human platelets.

Human natural killer cytotoxic activity is not affected by in vitro exposure to 50-Hz sinusoidal magnetic fields

Epidemiological studies have suggested, but not demonstrated, a role of exposure to 50/60-Hz magnetic fields in increasing cancer risk in man (workers and the general population). A possible target of magnetic fields is the immune system. In particular, it is known that an important defence against cancer is represented by natural killer (NK) cells capable of killing cancer cell targets. To test this hypothesis, human NK cells, stimulated or not with phytohaemagglutinin or interleukin 2, were exposed to 50-Hz sinusoidal magnetic fields before or during the cytotoxicity test, and then mixed with a variety of target cancer cell lines (Daudi, Raji, U937, H14, IGROV, SW626, K562, HL60). The experiments were performed in two laboratories (Rome and Modena) by means of two different exposure systems. The results of both laboratories suggest that 50-Hz sinusoidal magnetic fields with flux densities up to 10 mT do not affect the cytotoxic activity of human NK cells.

Intravenous immunoglobulins suppress immunoglobulin productions by suppressing Ca(2+)-dependent signal transduction through Fc gamma receptors in B lymphocytes

A high dose intravenous immunoglobulin (IVIG) therapy is used in the treatment of a wide range of autoimmune disorders. However, the mechanisms of the action of IVIGs remain poorly understood. To analyse the mechanisms of effects of IVIGs on immunoglobulin (Ig) production of B cells, the effects of IVIGs on B lymphoblastoid cell lines transformed by Epstein-Barr virus (LCLs) were investigated. The productions of IgG or IgM of LCLs were dose-dependently suppressed by polyethylene glycol (PEG)-treated IVIG or pH 4-treated IVIG though the productions were not or only slightly suppressed by pepsin-treated IVIG. The suppression by IVIGs was blocked by anti-human IgG Fc or anti-Fc gamma RII. C mu gene expression and mu s C terminal gene expression of LCLs were suppressed by PEG-treated IVIG, whereas neither C mu gene expression nor mu s C terminal gene expression of LCLs were suppressed by pepsin-treated IVIG. Although the increase in intracellular calcium concentration in LCLs was not suppressed by pepsin-treated IVIG, the increase was suppressed by PEG-treated IVIG. This suppressing effect of PEG-treated IVIG on intracellular calcium concentration of LCLs was blocked by anti-human IgG Fc or anti- Fc gamma RII. Our results suggest that IVIGs suppressed the Ca(2+)-dependent signal transduction through Fc gamma R on B-cell membrane, consequently, the transcription of C mu mRNA, especially secreted mu mRNA was suppressed in the B cells.

Ca2+ release and Ca2+ entry induced by rapid cytosolic alkalinization in Jurkat T-lymphocytes

4-Aminopyridine (4-AP), a compound usually known as a K(+)-channel inhibitor, induced rapid cytosolic alkalinization from pH 7.15 to pH 7.4, and subsequently Ca2+ mobilization in the T-lymphocyte cell line Jurkat. Other weak bases, such as NH4Cl or triethanolamine, induced a smaller and/or slower increase in cytosolic pH, resulting in a lower or no detectable Ca2+ signal. In the presence of extracellular Ca2+, 4-AP mediated a rapid and sustained increase in the free cytosolic Ca2+ concentration similar to that obtained by T-cell receptor-mediated stimulation. In the absence of extracellular Ca2+, 4-AP transiently released Ca2+ from an intracellular store that is most likely identical with the agonist- and Ins(1,4,5)P3-sensitive Ca2+ pool of Jurkat T-cells. As possible mechanisms for Ca2+ release from this particular pool as induced by 4-AP we examined (i) formation of Ins(1,4,5)P3 and (ii) sensitization of the Ins(1,4,5)P3-receptor/Ca(2+)release system by increasing intracellular pH. Although 4-AP did not induce formation of inositol polyphosphates, as demonstrated by h.p.l.c. analysis, in permeabilized cells the dose-response curve for Ins(1,4,5)P3 was shifted to the left by changing the intracellular pH from 7.2 to 7.4. This indicated that sensitization of the Ins(1,4,5)P3-receptor/Ca(2+)-release system was responsible for the effects of 4-AP seen in intact cells. In conclusion, 4-AP appears a novel tool for depletion of the agonist-sensitive Ca2+ pool of T-cells without simultaneous formation of Ins(1,4,5)P3, thereby inducing capacitative Ca2+ entry in these cells.

Target cell-directed degradation of perforin mRNA in CTL: lack of correlation with loss of protein and lytic ability

We have previously shown that CTL and NK cells rapidly down regulate perforin mRNA and become functionally inactive within 4-6 hr after exposure to sensitive target cells (TC). We report here for the first time that CTL also down regulate perforin mRNA upon exposure to resistant, but binding, TC. When three separate human MHC-restricted CTL lines were exposed to resistant TC, perforin mRNA was rapidly degraded. Removal of both extracellular Ca++ and Mg++ prevented perforin message down regulation, whereas removal of Ca++ alone did not, indicating that CTL:TC binding was required. Unlike the response of CTL exposed to sensitive TC, resistant TC did not trigger serine esterase (SE) release, suggesting distinct signalling pathways for perforin mRNA down regulation and granule exocytosis. Moreover, using western analysis, we showed that there was limited (< 10%) perforin protein release after CTL:TC interaction, suggesting that CTL loss of lytic activity after exposure to sensitive TC is not due to massive depletion of perforin. Treatment of CTL with mAb to CD2, CD3, CD2 + CD3, CD8, Class I and LFA-1 did not induce perforin mRNA down regulation. Furthermore, mAb to CD2, CD3, CD8, Class I, Class II, CD54 and LFA-1 did not block TC-mediated perforin mRNA down regulation although lysis of TC was inhibited.

Two independently regulated Ca2+ entry mechanisms coexist in Jurkat T cells during T cell receptor antigen activation

Receptor-mediated Ca2+ influx was studied in the human leukaemic T cell line, Jurkat. Stimulation of these cells through the T cell antigen-receptor complex with OKT3 (an antibody against the CD3 molecules of the T cell antigen-receptor complex), or inhibition of the endoplasmic reticular Ca(2+)-ATPase with thapsigargin, resulted in Ca2+ mobilization from intracellular stores and the activation of Ca2+ and Mn2+ entry. The rates of thapsigargin-induced Ca2+ and Mn2+ entry in Jurkat cells were 76% and 64% respectively of those observed after treatment of these cells with OKT3. The combined addition of thapsigargin plus OKT3 to Jurkat cells produced an enhanced effect on the sustained increase in the cytosolic free Ca2+ concentration that was greater than that obtained by addition of thapsigargin or OKT3 alone. The rates of Ca2+ and Mn2+ entry were increased to 119% and 112% respectively of the OKT3-induced rates. Taken together, these results suggest that the inositol 1,4,5-trisphosphate-sensitive Ca(2+)-pool-dependent bivalent cation entry only accounts for 57% and 52% respectively of the total OKT3-dependent Ca2+ and Mn2+ entry, and that the rest is mediated by second messenger(s). Thus two separate pathways coexist in regulating Ca2+ entry in Jurkat cells during activation mediated through the T cell receptor.

Defective calcium-dependent signal transduction in T lymphocytes of ataxia-telangiectasia

T-cell functions of two patients with ataxia-telangiectasia were investigated. Patients with ataxia-telangiectasia had reduced percentages of circulating CD3+ cells and CD4+ cells, although neither patient had a reduced percentage of circulating CD8+ cells. The proliferative responses and interleukin-2 production of peripheral blood mononuclear cells to T-cell mitogens were reduced in the patients. The intracellular calcium concentration in T cells or CD4+ cells from both patients was only slightly increased after phytohaemagglutinin stimulation. Moreover, the concentration after OKT3 stimulation was not or only slightly increased in T cells or CD4+ cells from both patients. Our results suggest that the functional defect of T cells is caused by defective Ca(2+)-dependent signal transduction through the CD3 complex of the surface in T cells of ataxia-telangiectasia.

Intracellular Ca2+ pools in Jurkat T-lymphocytes

Jurkat T-lymphocytes comprise at least four intracellular Ca2+ pools. Pool I was agonist-sensitive and contained 23 +/- 8% (n = 18) of the total Ca(2+)-storage capacity, as shown in intact cells in the presence of EGTA. The time courses of the agonist-induced formation of Ins(1,4,5)P3 and of the Ca2+ release from pool I were nearly superimposable, indicating that the agonist-sensitive pool I is emptied by Ins(1,4,5)P3. Likewise, in permeabilized cells, the size of the Ins(1,4,5)P3-sensitive Ca2+ pool I was 27 +/- 11% (n = 14). Pool II contained 26 +/- 5% (n = 9) of intracellularly stored Ca2+ and was liberated by thapsigargin, an inhibitor of the endoplasmic-reticulum (ER) Ca(2+)-ATPase. Addition of thapsigargin before addition of agonist abolished the agonist-induced Ca2+ release in both intact and permeabilized cells, indicating that pool I is a subcompartment of the ER Ca2+ pool. The content of this ER Ca2+ pool (pools I and II) amounted to 51 +/- 15% (n = 9) in intact cells and 49 +/- 16% (n = 16) in permeabilized cells. Caffeine released Ca2+ even when the ER pool (pools I and II) was emptied by previous addition of thapsigargin, indicating the presence of a third pool independent of pools I and II. Pool III contained 23 +/- 6% (n = 8) in intact cells, but 41 +/- 8% (n = 5) in permeabilized cells. The remaining intracellularly stored Ca2+ was released by addition of the Ca2+ ionophore ionomycin. This fourth pool contained 27 +/- 8% (n = 9) in intact cells, but less than 10% in permeabilized cells. The size of pool III was increased when pools I and II were emptied before addition of caffeine, whereas the size of pool IV was decreased under such conditions. In conclusion, this first comprehensive description of intracellular Ca2+ pools in Jurkat T-lymphocytes demonstrates the presence of four different Ca2+ pools, provides estimates of their sizes and describes relationships between each other. Release of Ca2+ from pool I [Ins(1,4,5)P3-sensitive] has previously been shown to play a major role in T-cell activation, whereas the physiological role of pools II-IV remains to be established.

Dual effects of oleic acid on Ca2+ mobilization and protein phosphorylation in human platelets in presence or absence of platelet activating factor

This laboratory demonstrated earlier that oleic acid inhibited platelet activating factor (PAF)-induced aggregation and serotonin release of rabbit platelets (M. Miwa, C. Hill, R. Kumar, J. Sugatani, M. S. Olson, and D. J. Hanahan, 1987, J. Biol. Chem. 262, 527-530). More recently, we reported that oleic acid caused a decrease in phosphatidylinositol-4-phosphate (PIP) and phosphatidylinositol-4,5-bisphosphate (PIP2), but did not affect the level of inositol-1,4,5-trisphosphate (IP3), in rabbit platelets (D. Nunez, J. Randon, C. Gandhi, A. Siafaka-Kapadai, M. S. Olson, and D. J. Hanahan, 1990, J. Biol. Chem. 265, 18330-18838). These results suggested that oleic acid did not stimulate phospholipase C. In contrast, PAF induced a decrease in PIP2 and an increase in PIP level and IP3. These effects were shown to be attenuated by oleic acid. In this current study, our experiments show that (a) oleic acid blocked PAF-induced rise in intracellular [Ca2+] (to provide a mechanism in agreement with our previous experiments which showed that oleic acid inhibited PAF-induced IP3 rise in platelets) and (b) oleic acid itself induced a gradual rise in [Ca2+]i, which would provide a mechanism for oleic acid-induced aggregation despite the fact that oleic acid did not cause the production of IP3 (Nunez et al., 1990). Oleic acid, in a dose-dependent manner, was shown to inhibit PAF-induced Ca2+ mobilization from intra- and extracellular sources. The inhibition was closely related to the suppressive effect of oleic acid on PAF-induced aggregation. Furthermore, oleic acid inhibited the PAF-stimulated phosphorylation of the 20- and 40-kDa proteins. At concentrations above 20 microM, oleic acid itself could induce platelet aggregation and Ca2+ mobilization, but the time sequence of these two responses in human platelets was significantly different from those obtained with PAF. Oleic acid alone, at 20 microM, caused a 1.4-fold increase in the cAMP level in platelets which was followed by a decline to a basal value at higher concentrations of this fatty acid. It seemed clear that elevation of adenylate cyclase activity was not associated with free fatty acid inhibition of platelet activation. Interestingly, both PAF and oleic acid added separately to human platelets induced protein-tyrosine phosphorylation, but oleic acid did not cause any inhibition of PAF-induced protein-tyrosine phosphorylation.(ABSTRACT TRUNCATED AT 400 WORDS)

Impaired proliferative responses of peripheral blood B cells from splenectomized subjects to phorbol ester and ionophore

The responses of peripheral blood B cells to mitogenic stimulation were examined in 12 splenectomized subjects without residual splenic function, as determined by pitted erythrocyte counts. These were compared to a group of healthy controls matched for age and sex. Polyclonal anti-immunoglobulin evoked a normal transient elevation in intracellular free Ca2+ in splenectomized subjects, thereby suggesting that the early events of the signal transduction pathway are not impaired. However, mitogenic stimulation by pre-treatment with phorbol ester and culture in presence of a calcium ionophore (Ionomycin) resulted in reduced uptake of 3H-thymidine and subsequent proliferation. Nevertheless, entry into the mitotic cycle, as assessed by expression of Ki67, was slightly, but not significantly impaired. Unlike in normal controls, where up to 7% of freshly-isolated B cells were Ki67+, almost no Ki67+ peripheral B cells were observed in splenectomized subjects. The data are consistent with the hypothesis that peripheral B cells in splenectomized subjects are in a reduced state of activation compared with normal controls and require additional growth factor stimulation before they can undergo mitosis.

Cytoplasmic calcium fluxes induced in cytotoxic effector cells by engagement of Fc gamma receptors I, II, and III

Changes in the intracellular calcium ion concentration ([Ca2+]i) of monocytes, granulocytes, and NK cells have been studied following either (1) independent cross-linking of Fc gamma receptors (Fc gamma R) I, II, or III, with F(ab gamma')2 fragments of monoclonal antibodies; or (2) linking of a selected Fc gamma R to a tumour cell target with bispecific F(ab' gamma)2 antibodies. Upon cross-linking each Fc gamma R with antibody an increase in the [Ca2+]i was observed, although all receptors apart from Fc gamma RIII on NK cells required additional cross-linking with an anti-mouse Fab' gamma. These results indicate that each type of receptor can transduce signals to the cell independently. Bispecific antibodies (anti-Fc gamma R x anti-target) linking cytotoxic Fc gamma R-bearing effector cells to tumour target cells also mediated increases in [Ca2+]i for all Fc gamma R tested except for Fc gamma RIII on granulocytes. The failure to transduce a signal via this receptor may be related to the GPI link, which is in contrast to the transmembrane link of Fc gamma RIII on NK cells. Significant lysis of tumour cell targets occurred when bispecific antibodies recruited NK cells or monocytes, but not granulocytes, via Fc gamma R. Chelation of intracellular Ca2+ in the effector cells reduced the observed lysis, suggesting a role for Ca2+ in the pathways leading to cytotoxicity.

Intracellular free Ca2+ fluxes and responses to phorbol ester in T lymphocytes from healthy elderly subjects

A group of healthy elderly subjects (greater than or equal to 75 years) was selected by the strict criteria of the SENIEUR protocol, and compared with healthy young (less than or equal to 35 years) volunteers. Mitogenic responses of peripheral blood mononuclear cells to phytohaemagglutinin and anti-CD3 were significantly reduced in the elderly (P less than 0.0002), thereby confirming that even though in perfect health, elderly individuals show impaired cell-mediated immunity. However, no abnormality of intracellular free Ca2+ fluxes could be detected in purified T cells from the elderly subjects when stimulated with anti-CD3 antibody. Nevertheless, both the proliferative responses of purified T cells to phorbol ester and calcium ionophore (Ionomycin) and the phorbol ester-induced inhibition of the Ca2+ response were defective in the elderly subjects (P less than 0.003 and P less than 0.0002, respectively). These data suggest that signal transduction and the generation of second messengers proceed normally in T cells from the elderly, but downstream events mediated by activation of protein kinase C are dysfunctional.

Beta-endorphin effects on membrane transduction in human lymphocytes

The endogenous opioid beta-endorphin (beta E) enhances, decreases or has negligible effects on cytotoxic and proliferative responses of lymphocytes. In order to characterize the mechanisms by which beta E modulates lymphocyte functions, we have examined the effects of beta E on certain membrane transduction events. We have shown that beta E inhibits phosphoinositol phosphate metabolism, and that it can enhance or inhibit the phosphorylation of the gamma chain of CD3 in a dose-dependent manner. We present the hypothesis that beta E contemporaneously modulates several membrane transduction processes, some of which may be counteracting and thereby producing the observed mixed effects on many lymphocyte functional responses. The biochemical status of the donor's lymphocytes also contributes to the variability in beta E-mediated effects on CMI outcomes.

Detection of antigen specific T lymphocytes by determination of intracellular calcium concentration using flow cytometry

We present a method for the detection of lymphocytes with specific reactivity to antigens on stimulator cells using flow cytometry. Cultured human T lymphocytes were loaded with the intracellular fluorochrome indo-1 and were mixed with stimulator cells. Using flow cytometry we could detect a specific increase in intracellular calcium in the T lymphocytes as well as conjugation between the T cells and the stimulator cells. Examination of antigen-specific CD4+ and CD8+ T cell clones demonstrated that the vast majority of T cells which were conjugated to antigen-bearing stimulator cells manifested a rapid increase in intracellular calcium. In contrast T cells conjugated to stimulator cells which did not bear specific antigen demonstrated no such increase in calcium. A similar finding was observed when examining polyclonal tumor infiltrating lymphocytes obtained from patients with melanoma. Tumor infiltrating lymphocytes with specific antitumor reactivity demonstrated an increase in intracellular calcium when conjugated to autologous tumor but not to allogeneic melanoma. In contrast to the T cell clones, only a small subpopulation of tumor infiltrating lymphocytes manifested this specific signal upon conjugation with autologous tumor. This suggests that tumor infiltrating lymphocyte cultures contain T cells with varying reactivities to tumor or may also imply heterogeneity in the stimulating tumor cell lines. The method allows for the detection of specific T cells on an individual cell basis in real time. The procedure is not lethal to the cell and sorting and subculturing of reactive T cell populations can be readily performed. The method could also be used to sort stimulator cells based on their ability to elicit an increase in intracellular calcium in selected T cells.

Potentiation of transmembrane signaling by cross-linking of antibodies against the β chain of the T cell antigen receptor of JURKAT T cells

Three monoclonal antibodies (mAb) 2D1, 3B9, and 3B12 were produced by immunizing BALB/c mice with JURKAT cells. These mAb induce comodulation of the TCR/CD3 complex expressed on JURKAT cells, but do not react with the CD3- JURKAT variant, J.RT3.T3.1. Immunoprecipitation studies with detergent-solubilized JURKAT cell lystes indicate that these mAb react with proteins having characteristics of the TCR molecules. Their low reactivity with peripheral blood mononuclear cells (PBMC) and lack of reactivity with other CD3+ T cell lines suggest that they may be anti-idiotypic mAb. Results from binding inhibition assays, reactivity with PBMC, and generation of transmembrane signals suggest that these three anti-TCR mAb recognized different epitopes on the TCR beta chain of JURKAT cells. Although the three mAb are capable of inducing the production of inositol phosphates and cytosolic free Ca2+ increase in JURKAT cells, their stimulatory capacities vary and are lower than that observed by anti-CD3 antibody (OKT3) stimulation. However, crosslinking these mAb with rabbit antimouse immunoglobulins potentiates the stimulatory response to comparable levels induced by OKT3. These mAb could be useful as tools to study V beta 8+ T cells in relation to antigen-specific activation.

Beta-endorphin blunts phosphatidylinositol formation during in vitro activation of isolated human lymphocytes: preliminary report

We have previously described the regulatory effect of beta-endorphin on three human cytotoxic cell populations. We confirmed the variable nature of these effects on human natural killer cell (NK) activity, showed mixed effects on the generation of cytotoxic T lymphocyte (CTL) activity, and demonstrated the reproducible suppression of lymphokine-activated killer cell (LAK) activity. We and others also observed mixed effects of beta-endorphin on the proliferative response to mitogens and in mixed leukocyte reactions. In the study reported here, we test the effects of beta-endorphin on the formation of phosphatidylinositol during cell activation. 32P-radiolabeled peripheral blood mononuclear cells obtained from normal adult donors and CD2-depleted subpopulations were activated with phytohemagglutinin or in a NK, LAK, or CTL protocol in the absence or presence of recombinant beta-endorphin. The total lipidic extract was analyzed by thin-layer chromatography and autoradiography. The results of these studies indicate that beta-endorphin blunts the formation of phosphatidylinositol by about 20% in the four systems studied and in all the donors tested. This effect is dose-dependent and is blocked in part by the opioid antagonist, naltrexone, suggesting involvement of the opioid receptor.

Alteration in Ca2+ homeostasis by a trauma peptide

Postinjury tissue inflammation with PMN elastase proteolysis generates immunosuppressive fibronectin peptides (FNDP) impairing chemotaxis, T-cell activation, and proliferation. Excess intracellular Ca2+ ([Ca2+]i) impairs T-cell activation. This study quantifies the changes in [Ca2+]i following exposure to a degradation peptide of fibronectin to determine the mechanism of action of these peptides on calcium homeostasis. Isolated human PBLs were exposed to immunosuppressive concentrations of FNDP after loading with the [Ca2+]i probe FURA-2AM. Resting and sustained [Ca2+]i concentrations were calculated and compared to buffer control. The mechanism of action was determined by pretreatment with: (1) EDTA binding extra cellular Ca2+: [Ca2+]e, (2) the Ca2+ channel blockers verapamil and nifedipine, and (3) inhibition of [Ca2+]i released by dantrolene. Inositol triphosphate (IP3) essential for [Ca2+]i release was measured following T-cell stimulation as well. FNDP caused 200-400% increases in [Ca2+]i concentration relative to buffer control at known suppressive doses. Verapamil and nifedipine partially block [Ca2+]i influx by as much as 50% suggesting the slow Ca2+ (voltage independent) channels are partially responsible for the increased [Ca2+]i seen following FNDP. EDTA completely suppressed [Ca2+]e influx but did not completely inhibit the release of [Ca2+]i although IP3 was 80% suppressed. The increase in [Ca2+]i following FNDP stimulation is due to release of intracellular stores.

The protein kinase C inhibitor 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7) inhibits PMA-induced promiscuous cytolytic activity but not specific cytolytic activity by a cloned cytolytic T lymphocyte

Phorbol 12-myristate 13-acetate (PMA) induces the cytolytic T lymphocyte (CTL) clone 4D (H-2b anti-H-2d) to promiscuously kill the inappropriate target EL-4 (H-2b). The protein kinase C (PKC) inhibitor 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7) inhibited the PMA-induced promiscuous lympholysis. The concentration of H-7 that inhibited PMA-induced lympholysis by 50% (IC50) was calculated to be 4 microM, which closely approximates the reported IC50 of H-7 of 6 microM for PKC activity in vitro. In striking contrast, specific cytolysis of appropriate P815 (H-2d) target cell by CTL clone 4D was not inhibited by concentrations of H-7 which inhibited PMA-induced promiscuous lympholysis. These results indicate that PMA-induced promiscuous lympholysis of inappropriate target cell is triggered via activation of PKC, whereas PKC activation is not obligatory in triggering CTL clone 4D to specifically kill appropriate target cells. Thus, these data suggest that cloned CTL have two or more triggering mechanisms than may initiate one or more cytolytic pathways.

Cytotoxic T lymphocyte (CTL)-mediated cytolysis proceeds in the absence of Na+/H+ antiport activity: regulation of cytosolic pH by the Na+/H+ antiport in a cloned CTL

Cytotoxic T lymphocyte (CTL)-mediated cytolysis of specifically bound target cells (TC) is thought to be triggered by cross-linking the T-cell antigen receptor (TcR). Biochemical events associated with TcR cross-linking include increased intracellular calcium levels [Ca2+]i, hydrolysis of phosphatidylinositol (PI), and an increase in intracellular pH [pH]i. Whereas CTL-mediated cytolysis of some TC is calcium-dependent, and PI hydrolysis is speculated to trigger the CTL lethal hit via activation of PKC, little is known about changes in [pH]i relating to activation of the lethal hit stage. We report regulation of [pH]i in a cloned CTL by the electroneutral Na+/H+ antiport during activation with PMA and specific antigen-bearing TC. Furthermore, using 5-(N-methyl-N-isobutyl) amiloride (MIBA), a potent antiport inhibitor, we demonstrate that Na+/H+ exchange is not required for activation of CTL cytolytic activity.

Modification of membrane phospholipid fatty acyl composition in a leukemic T cell line: effects on receptor mediated intracellular Ca2+ increase

The effect of modifying fatty acyl composition of cellular membrane phospholipids on receptor-mediated intracellular free Ca2+ concentration ([Ca2+]i) increase was investigated in a leukemic T cell line (JURKAT). After growing for 72 h in medium supplemented with unsaturated fatty acids (UFAs) and alpha-tocopherol, the fatty acyl composition of membrane phospholipids in JURKAT cells was extensively modified. Each respective fatty acid supplemented in the culture medium was readily incorporated into phosphatidylinositol, phosphatidylserine, phosphatidylethanolamine and phosphatidylcholine in the JURKAT cells. The total n-6 fatty acyl content was markedly reduced in phosphatidylinositol and phosphatidylcholine of cells grown in the presence of n-3 fatty acids (alpha-linolenic acid, eicosapentaenoic acid and docosahexaenoic acid). Conversely, in the presence of n-6 fatty acids (linoleic acid and arachidonic acid), the total n-3 fatty acyl content was reduced in all the phospholipids examined. In n-3 and n-6 polyunsaturated fatty acid (PUFA) modified JURKAT cells, the total n-9 monounsaturated fatty acyl content in the phospholipids were markedly reduced. Changing the fatty acyl composition of membrane phospholipids in the JURKAT cells appears to have no affect on the presentation of the T cell receptor/CD3 complex or the binding of anti-CD3 antibodies (OKT3) to the CD3 complex. However, the peak increase in [Ca2+]i and the prolonged sustained phase elicited by OKT3 activation were suppressed in n-3 and n-6 PUFA but not in n-9 monounsaturated fatty acid modified cells. In Ca2+ free medium, OKT3-induced transient increase in [Ca2+]i representing Ca2+ release from the inositol 1,4,5-trisphosphate-sensitive Ca2+ stores, were similar in control and UFA modified cells. Using Mn2+ entry as an index of plasma membrane Ca2+ permeability, the rate of fura-2 fluorescence quenching as a result of Mn2+ influx stimulated by OKT3 in n-9 monounsaturated fatty acid modified cells was similar to control cells, but the rates in n-3 and n-6 PUFA modified cells were significantly lower. These results suggest that receptor-mediated Ca2+ influx in JURKAT cells is sensitive to changes in the fatty acyl composition of membrane phospholipids and monounsaturated fatty acids appears to be important for the maintenance of a functional Ca2+ influx mechanism.

Structural analysis of the CD69 early activation antigen by two monoclonal antibodies directed to different epitopes

The biochemical structure of CD69 early activation antigen has been characterized by means of two newly isolated mAb, namely C1.18 and E16.5. Upon analysis by SDS-PAGE, C1.18-reactive molecules immunoprecipitated from 125I-surface labeled PMA activated PBL consisted of a 32 + 32 kD dimer, a 32 + 26 kD dimer, a 26 + 26 kD dimer and a 21 + 21 kD dimer. E16.5-reactive molecules consisted of a 26 + 26 kD dimer and a 21 + 21 kD dimer. Cross absorption experiments showed that E16.5 mAb reacts with an epitope of the CD69 molecule distinct from the one recognized by C1.18 mAb and present only on a subpopulation of the CD69 molecular pool. The patterns of migration of C1.18- and E16.5-reactive molecules in two-dimensional gel-electrophoresis, under reducing conditions before and after treatment with Endoglycosidase F enzyme suggest that the two mAb recognize the same glycoprotein structure, but in two distinct glycosylation forms, both expressed on the cell surface membrane. Finally, p32, p26 and p21 of CD69 complex obtained from three distinct normal donors did not show appreciable structural polymorphism, by two-dimensional peptide mapping, not only among single subunits within the same individual, but also among homologous subunits in distinct individuals. Further, it was found that CD69 complex is expressed at the cell surface of resting PBL, although at a very reduced level in comparison to PMA activated cells. C1.18 and E16.5 mAb induced comparable cell proliferation and IL-2 production in PBL in the presence of PMA. C1.18 mAb increased intracellular free calcium concn in PMA activated PBL after cross-linking with goat anti mouse Ig, while the effect induced by E16.5 mAb after cross-linking was consistently lower. Finally, it was found that Sepharose-linked C1.18 mAb, in the presence of rIL-2 or PMA, did not induce TNF release from 6 NK cell clones.

Extracellular ATP as a possible mediator of cell-mediated cytotoxicity

Cytotoxic T lymphocytes (CTL) and natural killer (NK) cells lyse target cells by a specialized mechanism that involves the release of soluble 'killer' mediators. While several possible mediators have been demonstrated, it is likely that others have yet to be identified. For more than two decades it has been known that exogenous ATP is lytic to many cell types. In this article Francesco Di Virgilio and colleagues propose that extracellular ATP may be a mediator of cytotoxic cell-dependent lysis.

Activation of polyphosphoinositide hydrolysis in T cells by H-2 alloantigen but not MLS determinants

Murine minor lymphocyte-stimulating (Mls) determinants are cell surface antigens that stimulate strong primary T cell responses; the responding T cells display restricted T cell receptor (TCR) V beta gene usage. Interaction of T cells with mitogens or major histocompatibility complex (MHC) antigens activated the polyphosphoinositide (PI) signaling pathway, but this pathway was not triggered by Mls recognition. However, interleukin-2 (IL-2) secretion and proliferation to all three stimuli were comparable. Thus, although recognition of both allo-H-2 and Mls determinants is thought to be mediated by the TCR, these antigens appear to elicit biochemically distinct signal transduction pathways.

A central role for phosphoinositide hydrolysis in activating the lytic mechanism of human natural killer cells

Using neomycin, which inhibits phosphoinositide breakdown, cytotoxicity mediated by natural killer (NK) cells was suppressed in a dose-dependent manner, with complete inhibition at 16 mM. Generation of inositol phosphates in effector cells after target cell binding was inhibited in the presence of neomycin. The formation of effector to target cell conjugates was not affected. Neomycin-induced inhibition of NK killing was abolished when TPA was added to the cytotoxic assays. This reconstitution was dependent upon extracellular Ca2+. When the intracellular free Ca2+ level in effector cells was reduced from 73 +/- 11 nM to 43 +/- 3 nM (n = 4) using the Ca2+ indicator dye, Quin 2, NK killing was markedly reduced. Inhibiting the enzyme diacylglycerol (DG) kinase in effector cells with 10 microM R59022 (DG kinase inhibitor) potentiates NK killing, suggesting an increase in protein kinase C (PKC) activity due to accumulation of DG. The PKC inhibitor, H-7, suppressed NK killing in a concentration-dependent manner. These results demonstrate that phosphoinositide metabolism is an early event and its derived second messengers play a central role in activating the lytic mechanism of NK cells.

Inhibition of Fura-2 sequestration and secretion with organic anion transport blockers

Fura-2 is widely used to measure the concentration of cytosolic free calcium, but in many cells the dye does not remain localized within the cytoplasmic matrix. In these cells, Fura-2 is sequestered within intracellular organelles, secreted into the extracellular medium, or both. We have found that, in mouse peritoneal macrophages, J774 cells, PC12 cells, and N2A cells, Fura-2 sequestration and secretion are mediated by organic anion transport systems and are blocked by the inhibitors probenecid and sulfinpyrazone. Under appropriate conditions these agents have little affect on calcium transients, and may facilitate the use of Fura-2 in a variety of cell types.

Mitogen-induced oscillations of cytosolic Ca2+ and transmembrane Ca2+ current in human leukemic T cells

A rapid rise in the level of cytosolic free calcium ([Ca2+]i) is believed to be one of several early triggering signals in the activation of T lymphocytes by antigen. Although Ca2+ release from intracellular stores and its contribution to Ca2+ signaling in many cell types is well documented, relatively little is known regarding the role and mechanism of Ca2+ entry across the plasma membrane. We have investigated mitogen-triggered Ca2+ signaling in individual cells of the human T-leukemia-derived line, Jurkat, using fura-2 imaging and patch-clamp recording techniques. Phytohemagglutinin (PHA), a mitogenic lectin, induces repetitive [Ca2+]i oscillations in these cells peaking at micromolar levels with a period of 90-120 s. The oscillations depend critically upon Ca2+ influx across the plasma membrane, as they are rapidly terminated by removal of extracellular Ca2+, addition of Ca(2+)-channel blockers such as Ni2+ or Cd2+, or membrane depolarization. Whole-cell and perforated-patch recording methods were combined with fura-2 measurements to identify the mitogen-activated Ca2+ conductance involved in this response. A small, highly selective Ca2+ conductance becomes activated spontaneously in whole-cell recordings and in response to PHA in perforated-patch experiments. This conductance has properties consistent with a role in T-cell activation, including activation by PHA, lack of voltage-dependent gating, inhibition by Ni2+ or Cd2+, and regulation by intracellular Ca2+. Moreover, a tight temporal correlation between oscillations of Ca2+ conductance and [Ca2+]i suggests a role for the membrane Ca2+ conductance in generating [Ca2+]i oscillations in activated T cells.

Progressive ankylosis (ank/ank) in mice: an animal model of spondyloarthropathy. III. Proliferative spleen cell response to T cell mitogens

Murine progressive ankylosis is a spontaneous disorder of mice resulting from a homozygous recessive genetic defect (ank/ank) which produces an inflammatory arthritis of peripheral and axial joints eventually resulting in ankylosis of these joints. This disorder resembles the human spondyloarthropathies clinically, radiographically and histologically. Various studies in humans with spondyloarthropathies have described defects of cellular immunity but these results are conflicting. We measured the spleen cell response to mitogen in ank/ank mice and in normal littermates. The spleen cell response to the T cell mitogens phytohaemagglutinin and concanavalin A was decreased in ank/ank mice compared with their normal littermates. The response to the B cell mitogen lypopolysaccharide was normal in both ank/ank mice and normal littermates. Serum from ank/ank mice did not inhibit spleen cell responses to mitogen. Ank/ank spleen cells were not inhibitory of normal spleen cell responses to mitogens. Addition of irradiated normal spleen cells to ank/ank spleen cells did not restore the mitogen responses to normal. It is possible that the ank/ank gene results in the phenotypic expression of an abnormal or decreased cell product involved in T cell proliferation. Several recently described cytokines could be potential candidates for this product.

FeLV-induced immunosuppression through alterations in signal transduction: changes in intracellular free calcium levels

Feline leukemia virus (FeLV) is a retrovirus with immunosuppressive properties. The mechanism(s) of immunosuppression is unknown. Calcium has been shown to be a second messenger in cellular activation and regulation. This study was designed to determine whether FeLV alters intracellular free calcium (IFC) levels in an FeLV-infected feline lymphoid cell line. Control cells and FeLV-infected cells were exposed to Concanavalin A, formyl-L-methionyl-L-leucyl-L-phenylalanine, and leukotriene B4. The basal IFC and post-stimulation IFC levels were recorded using Fura 2 AM and a luminescence spectrometer. Data collected indicate that FeLV-infected cells have a higher basal level of IFC and a reduced amount of increase in IFC after stimulation when compared to the control cells. The results would seem to indicate retrovirus-mediated interference occurring in the intracellular calcium signaling process.

An immunodeficiency characterized by defective signal transduction in T lymphocytes

We studied a nine-year-old boy with severe, recurrent infections. The patient was exposed in utero to azathioprine and prednisone. He had autoimmune hemolytic anemia, bronchiectasis, and Hodgkin's disease. The patient's circulating lymphocytes were normal in number and phenotype, but stimulation of the T-cell receptor by antigens, mitogens, and monoclonal antibodies failed to induce interleukin-2-receptor expression, interleukin-2 synthesis, or lymphocyte proliferation. The early biochemical events necessary to initiate lymphocyte activation--accumulation of the second messenger diacylglycerol, activation of the enzyme protein kinase C, and elevation of the free intracellular calcium concentration--failed to occur in this patient's lymphocytes. The defect in the lymphocyte could be corrected in vitro by two agents that bypass the receptor-mediated signal mechanism (the diacylglycerol analogue phorbol and the calcium ionophore ionomycin). Further studies localized the defect in signal transduction to the interaction between cell-surface receptors and the guanine nucleotide-binding protein. We conclude that this patient's immunodeficiency was caused by a defective coupling of surface receptors to signal-transducing proteins in his T lymphocytes, resulting in failure of lymphocyte activation.

Generation of inositol phosphates during triggering of cytotoxicity in human natural killer and lymphokine-activated killer cells

We investigated early molecular mechanisms involved in the triggering of cytolytic responses in natural killer (NK) and lymphokine-activated (LAK) cells. When NK or LAK cells were conjugated to the sensitive target cells K562, an increased formation of both inositol monophosphate (IP1) and inositol trisphosphate (IP3) was detected. Target cells like Raji or Jok-1, which form conjugates with NK cells but are insensitive to NK lysis, did not elicit IP1 formation. Treatment of NK cells with interleukin 2 increased the basal turnover of inositol phosphates and enhanced the phosphatidyl inositol breakdown upon confrontation with sensitive targets. These finding indicate that hydrolysis of phosphatidyl inositols is associated with the signal which triggers the cytolytic response in NK and LAK cells. These events therefore constitute an early marker of the cytolytic activation.

Contingent genetic regulatory events in T lymphocyte activation

Interaction of antigen in the proper histocompatibility context with the T lymphocyte antigen receptor leads to an orderly series of events resulting in morphologic change, proliferation, and the acquisition of immunologic function. In most T lymphocytes two signals are required to initiate this process, one supplied by the antigen receptor and the other by accessory cells or agents that activate protein kinase C. Recently, DNA sequences have been identified that act as response elements for one or the other of the two signals, but do not respond to both signals. The fact that these sequences lie within the control regions of the same genes suggests that signals originating from separate cell membrane receptors are integrated at the level of the responsive gene. The view is put forth that these signals initiate a contingent series of gene activations that bring about proliferation and impart immunologic function.

Phosphatidyl inositol hydrolysis after CD3 binding in human peripheral blood T cells: inhibition by prostaglandin E2

Hydrolysis of phosphatidyl inositol-4,5-bisphosphate, leading to generation of inositol phosphates (IPs), occurs after crosslinking CD3 antigens on the surface of murine and human T-cell lines and clones, and is thought to represent a basic mechanism of signal transduction after antigen receptor binding. Previous investigators have had difficulty demonstrating this phenomenon using human peripheral blood T-cells. In this paper we demonstrate significant IP generation after anti-CD3 stimulation of human peripheral blood lymphocytes and T-cells. The amount of IP generation is less and considerably more variable than what is obtained using a T-cell line. Also, exposure to ammonium chloride in the E-rosetting procedure totally inhibits IP generation, perhaps explaining previous unsuccessful attempts. Finally, prostaglandin E2 and other agents that raise cyclic AMP inhibit IP generation by anti-CD3 antibodies in human T-cells and a T-cell line.

Ultracytochemical study of capillary Ca2+-ATPase activity in brain edema

To investigate the functional relationship between astrocytes and Ca2+-ATPase of cerebral capillary endothelial cells (capillary Ca2+-ATPase), cold lesions were produced and the cytochemical reaction (CR) for Ca2+-ATPase activity and morphological changes of astrocytes were chronologically studied. Under normal conditions, CR for capillary Ca2+-ATPase activity was mild. However, at 20 min after the operation, astrocytic end-feet embracing the capillaries were swollen, and CR was moderate. Deposits of slightly coarsened reaction product (RP) appeared and accumulated on the abluminal surface. CR became stronger as edema fluid accumulated. At 4, 7 and 15 days, detachment of the astrocytic processes from the capillary wall was observed and in the uncovered capillaries, CR was intense, especially on the abluminal surface. It could be thus possible that the enzyme was related to the blood-brain barrier (BBB). At 2 months, reactive astrocytes had recovered lesion-resistant capillaries. CR was mild and its associated deposits were coarser, the number decreasing on both surfaces. The nature and localization of the deposits of RP in the scar were different from those under normal conditions, possibly due to the functional differences between normal and reactive astrocytes in the BBB. CR was mild in association with astrocytes embracing the capillary wall and was intense without astrocytes. Therefore, it might be possible that astrocytes exerted certain effects on capillary Ca2+-ATPase activity in relation to BBB function.

Inhibitors of membrane transport system for organic anions block fura-2 excretion from PC12 and N2A cells

The neuroblastoma-like cell line N2A and the pheochromocytoma-like cell line PC12 excrete about 20-25% of the intracellular fluorescent Ca2+ indicator fura-2 during 10 min of incubation at 37 degrees C. The drug probenecid, known to inhibit membrane systems for the transport of organic anions [Cunningham, Israili & Dayton (1981) Clin. Pharmacol. 6, 135-151], inhibited fura-2 excretion in both cell types. However, probenecid also had untoward effects on intracellular Ca2+ homeostasis in N2A and PC12 cells. We therefore tested the drug sulphinpyrazone, another known inhibitor of organic-anion transport systems. Sulphinpyrazone fully inhibited excretion of fura-2 at 250 microM, a concentration one order of magnitude lower than that of probenecid. At this concentration and for incubation times up to 20 min, sulphinpyrazone had no untoward effects on cell viability and metabolic functions. Fura-2 was also loaded into the cytoplasm of N2A cells by permeabilization of the plasma membrane with extracellular ATP. In this case as well, the dye was rapidly released from the cells and the efflux was blocked by sulphinpyrazone. These findings suggest that N2A and PC12 cells possess a membrane system for the transport of the free-acid form of fura-2. This transport system is probably responsible for the excretion of fura-2 from these cells. Incubation of N2A and PC12 cells with sulphinpyrazone may help overcome problems arising in the investigation of [Ca2+]i homeostasis in these cell types.

Dissociation of phosphoinositide hydrolysis and Ca2+ fluxes from the biological responses of a T-cell hybridoma

T lymphocytes can be activated in a variety of ways, including occupancy of the T cell antigen receptor (TCR) complex or cross-linking of certain cell-surface molecules with antibody. Two of the earliest events seen after stimulation are the hydrolysis of phosphatidylinositol bisphosphate to inositol trisphosphate (Ins P3) and 1,2-diacylglycerol (DAG), and an increase in the concentration of intracellular Ca2+ ([Ca2+]i). Later, the cell secretes lymphokines and expresses lymphokine receptors. It has been postulated that the products of the hydrolysis of phosphatidylinositols (Ptd Ins) and fluctuations in [Ca2+]i are critical 'second messengers', transmitting the signals for the initiation of the later events. We have examined the relationship between these second messengers and the secretion of IL-2 in a murine T cell variant whose missing TCR complex had been reconstituted by gene transfer. Surprisingly, although the IL-2 responses of the transfectant could not be distinguished from the original line expressing the same TCR, Ptd Ins hydrolysis and the increase in [Ca2+]i were substantially reduced or absent in the reconstituted cell. It is therefore possible to dissociate these early biochemical changes from a late biological response, raising questions about the putative causal relationship of these events.