Relevance of clinical and laboratory findings in the diagnosis of cytomegalovirus encephalitis in patients with AIDS

A retrospective evaluation was conducted in patients with AIDS and an autopsy diagnosis of cytomegalovirus (CMV) encephalitis to determine the relevance of clinical and laboratory findings in establishing a diagnosis. On autopsy of 100 patients, CMV encephalitis was diagnosed in 13 patients; eight had periventricular CMV encephalitis, four micronodular CMV encephalitis, and one both conditions. Seven patients had had a CMV infection previously (6 cases of retinitis, 1 case of colitis), and at the onset of encephalitis all of them were receiving a maintenance dose of ganciclovir. Examination of the CSF showed specific changes in patients with periventricular encephalitis. CT revealed no characteristic findings, while MRI showed an increased signal intensity on T2 weighted images. CMV DNA amplification by nested PCR was performed in nine patients with CMV encephalitis; PCR was positive in eight patients whose CSF was collected during CMV encephalitis, and negative in one patient whose CSF was collected six months before death. In conclusion, some clinical findings suggest a presumptive diagnosis, especially of periventricular encephalitis, and nested PCR appears to be a reliable and rapid technique for making an antemortem diagnosis.

Cytometric analysis of immunosenescence

We have been studying the immune system of healthy centenarians for many years, and they provide the best example of successful aging. They are people who have escaped major age-related diseases and reached the extreme limit of human life in good clinical condition. In most cases, histories of centenarians reveal them to be free of cancer, dementia, diabetes, cardiovascular diseases, and cataracts. Moreover, in order to reach such an advanced age, they should be equipped with well preserved and efficient immuno- and defense mechanisms, and optimal combinations of an appropriate lifestyle and genetic background. Using this approach, several paradoxes emerged as far as the immune system of centenarians is concerned, regarding: i) humoral immunity (increase in plasma immunoglobulins and nonorgan-specific autoantibodies, decrease in B cell number and lack of organ-specific autoantibodies); ii) cellular immunity (well preserved number of "virgin" T cells, a relatively intact T cell repertoire despite a thymus involuting since puberty, increased number of cells with markers of NK activity); iii) decreased peripheral blood lymphocyte tendency to programmed cell death, associated with a well preserved mitochondria functionality and intracellular bcl-2 levels. An age-related increase in the levels of adhesion molecule present on lymphocyte plasma-membrane, accompanied by a complex reshaping of the cytokine network, must be added to this scenario. All our data fit the hypothesis that a complex, unpredicted remodeling of the immune system occurs with age. In the present review it is underlined how flow cytometry has been used to study most of the above mentioned aspects of immunosenescence, and to establish new age-related reference values.

Different pathways of apoptosis revealed by 2-chloro-adenosine and deoxy-D-ribose in mammalian astroglial cells

Both the adenosine analogue 2-chloro-adenosine (2-CA) and the reducing sugar deoxy-D-ribose (dRib) induce apoptosis of astroglial cells in rat brain primary cultures (Abbracchio et al.: Biochem Biophys Res Commun 213:908-915, 1995). The present study was undertaken to elucidate by both morphological and cytofluorimetric analyses the intracellular mechanism(s) involved in induction of apoptosis by these two agents. The poly(ADP-ribose)polymerase (PARP) inhibitor 3-aminobenzamide did not prevent either 2-CA- or dRib-induced cell death, suggesting that activation of PARP is not critically important for induction of apoptosis in astrocytes. The radical scavenger N-acetyl-cysteine (NAC) strongly inhibited dRib- but not 2-CA-induced cell death, suggesting a differential role for radical formation in apoptosis by these two agents. A time-dependent increase of cells with depolarized mitochondria was observed in dRib-, and to a lesser extent, in 2-CA-treated cultures. NAC also prevented dRib- but not 2-CA-induced mitochondrial changes. We conclude that, in mammalian astrocytes, apoptosis can proceed through diverse and multiple pathways, depending upon the apoptotic stimulus. For dRib, apoptosis likely proceeds through generation of radicals and mitochondrial involvement. An adenosine extracellular receptor linked to an as yet unidentified signaling pathway may instead mediate 2-CA-induced cell death, which may have intriguing implications for both nervous system development and brain response to trauma and ischemia.

Mitochondria alterations and dramatic tendency to undergo apoptosis in peripheral blood lymphocytes during acute HIV syndrome

OBJECTIVE

To study alterations of mitochondrial membrane potential (delta psi) and the propensity to undergo apoptosis in peripheral blood lymphocytes (PBL) from subjects with acute HIV syndrome; and to evaluate possible modulations of these phenomena by antioxidants that can be used in therapy, such as N-acetyl-cysteine (NAC), nicotinamide (NAM), or L-acetyl-carnitine (LAC).

METHODS

Mitochondrial function and the tendency of PBL to undergo spontaneous apoptosis were studied on freshly collected PBL from patients with symptomatic, acute HIV-1 primary infection, which were cultured for different durations in the presence of absence of NAC. NAM or LAC. By a cytofluorimetric method allowing analysis of delta psi in intact cells, we studied the function of these organelles under the different conditions. PBL apoptosis was evaluated by the classic cytofluorimetric method of propidium iodide staining, capable of revealing the typical DNA hypodiploid peak.

RESULTS

Significant delta psi alterations and tendency to undergo apoptosis were present in PBL from the subjects we studied. Indeed, when cultured even for a few hours in the absence of any stimulus, a consistent number of cells died. However, the presence of even different levels of NAC, NAM or LAC was able to rescue most of them from apoptosis. Both a fall in delta psi and apoptosis were evident in PBL collected in the earliest phases of the syndrome (before seroconversion), and changed significantly after a few days. A significant correlation was found between spontaneous apoptosis and tumour necrosis factor (TNF)-alpha or p24 plasma levels, as well as between apoptosis and the percentages of circulating CD4+ or CD8+ T cells.

CONCLUSIONS

PBL from patients with acute HIV syndrome are characterized by both significant mitochondrial alterations and a dramatic tendency to undergo apoptosis. The use of NAC, NAM or LAC seems to rescue cells through a protective effect on mitochondria, a well-known target for the action of TNF-alpha and for reactive oxygen species, the production of which is strongly induced by this cytokine. Thus, our data could provide the rationale for the use of such agents in addition to antiviral drugs in primary infection.

A shift to Th0 cytokine production by CD4+ cells in human longevity: studies on two healthy centenarians

Centenarians, particularly healthy centenarians, constitute the example of successful aging and the study of their immune status can help to define the endpoint of the changes occurring throughout life. We characterized T cell clones (TCC) of two healthy centenarians, studying their phenotypes and production of representative Th1 and Th2 cytokines (IFN-gamma and IL-4) and compared them with TCC obtained by three young normal subjects; in all 180TCC were analyzed. In young donors, 35TCC were CD4+, 56CD8+ and 2 were alpha beta +CD4-CD8- (double negative). In centenarians, we obtained 46CD4+TCC, 38CD8+, 2CD4+CD8+ (double positive) and 1 gamma delta + double negative. Of the young subjects' TCC, 71% produced IFN-gamma but no IL-4 (Th1 pattern) and this prevalence decreased to 39% in TCC from the centenarians. The number of clones showing the opposite Th2 pattern was similar in young and aged donors (3 out of 93TCC and 2 out of 87TCC, respectively). The intermediate profile of TCC producing both IL-4 and IFN-gamma (Th0) was found in 25.8% of clones from young people, but it almost doubled to 58.6% in centenarians. The analysis shows that the Th profiles of CD8+TCC is nearly superimposable in the two groups, whereas a major shift from a Th1 to a Th0 pattern is presented by CD4+TCC. The balance provided by a majority of CD4+TCC showing a Th0 pattern may ensure both humoral and cell-mediated defences. In CD8+TCC, however, a Th1 pattern still is present, possibly for efficient generation of cytotoxic responses. These findings should be extended by studying other centenarians and elderly subjects.

TNF alpha alters mitochondrial membrane potential in L929 but not in TNF alpha-resistant L929.12 cells: relationship with the expression of stress proteins, annexin 1 and superoxide dismutase activity

Tumour necrosis factor alpha (TNF alpha) cytotoxicity is mediated, at least in part, by oxidative stress and phospholipase A2 activation. The first post-receptor events to be observed in TNF alpha-sensitive lines are the generation of superoxide anion (O2-) within the mitochondria and the activation of phospholipase A2. Using the lipophilic dye JC-1 to determine mitochondrial membrane potential, we showed that TNF alpha induces time-dependent alterations in mitochondrial membrane potential in L929 cells but not in the TNF alpha-resistant L929. 12 subclone. Heat shock (HS) proteins (HSP) and superoxide dismutase (SOD) have been shown to protect cells from TNF alpha cytotoxicity, while glucose regulated proteins (GRP) and annexins might also be involved in cellular protection. We thus compared the expression of HSP, grp78 and annexin 1 as well as SOD activity in TNF alpha sensitive and resistant lines. We found no difference in the expression of HSP, grp78 or annexin 1, but an increase in the constitutive activity of SOD in the L929.12 cells as compared to L929. Furthermore, SOD was inducible by TNF alpha in L929 cells, but not in L929.12 cells. These data suggest that in TNF alpha-resistant lines, mitochondrial damage by TNF alpha is prevented by an increase in SOD rather than in overexpression of stress proteins or annexins.

Earthworm coelomocytes in vitro: cellular features and "granuloma" formation during cytotoxic activity against the mammalian tumor cell target K562

Earthworms possess specific, adaptive, cellular immunodefense as well as non-specific responses found in other complex metazoans. Here we characterized coelomocytes from the earthworm Eisenia foetida by electron microscopy and cytofluorimetric analyses, and investigated structural changes that occur when effector coelomocytes and target K562 erythromyeloid human tumor cells interact during cytotoxic activity. In in vitro cultures 1) the two earthworm cell types (i.e. small and large coelomocytes) retained their morphological features; 2) their DNA content was significantly less than that of human lymphocytes and the erythromyeloid human tumor cell line K562; 3) significant percentages of coelomocytes were found to be in S or G2/M phases of the cell cycle. When cultivated alone for up to 3 h, coelomocytes formed no aggregates. However, when mixed with K562, coelomocytes spontaneously killed tumor cells, and cytotoxic reactivity was accompanied by the formation of multiple aggregates similar to granulomas. These results are the first to describe this type of earthworm non-specific "inflammatory" response in vitro against tumor cells.

Mitochondria are selective targets for the protective effects of heat shock against oxidative injury

Heat shock (HS) proteins (HSPs) induce protection against a number of stresses distinct from HS, including reactive oxygen species. In the human premonocytic line U937, we investigated in whole cells the effects of preexposure to HS and exposure to hydrogen peroxide (H2O2) on mitochondrial membrane potential, mass, and ultrastructure. HS prevented H2O2-induced alterations in mitochondrial membrane potential and cristae formation while increasing expression of HSPs and the protein product of bcl-2. Protection correlated best with the expression of the 70-kDa HSP, hsp70. We propose that mitochondria represent a selective target for HS-mediated protection against oxidative injury.

Earthworm leukocytes that are not phagocytic and cross-react with several human epitopes can kill human tumor cell lines

Earthworm coelomocytes (leukocytes) effect cytotoxicity at significantly high levels against the NK-sensitive, human tumor cell line, K562, and the NK-resistant targets (U937, BSM, CEM). By cytofluorimetric analyses using mouse anti-human monoclonal antibodies and by morphological evaluations, two types of coelomocytes were identified: (1) small (8-11 micron) electron-dense cells (SC): CD11a+, CD45RA+, CD45RO+, CDw49b+, CD54+, beta 2-m+ and Thy-1+; (2) large (12-15 micron) electron-lucent cells (LC) that are negative for these markers. Both cell types were negative for other CD and MHC class I and class II markers. SC were active during recognition, rapidly binding to targets; LC were phagocytic. Release of 51Cr revealed rapid, significant, and equal levels of killing at 4 degrees, 20 degrees, and 37 degrees C. We propose that primitive NK-like activity appeared early in evolution.

CD45 isoforms expression on CD4+ and CD8+ T cells throughout life, from newborns to centenarians: implications for T cell memory

CD4+ and CD8+ peripheral blood T lymphocytes show mutually exclusive expression of CD45RA or CD45R0, two isoforms of the common leukocyte antigen that seem to recognize so-called virgin/unprimed and memory/activated T cells. The expression of these isoforms has been studied by three colour cytofluorimetric analysis on CD4+ or CD8+ peripheral blood CD3+ cells from 22 healthy centenarians, analyzed in a context of 202 healthy donors 0-110 years old. An age-related unbalance of virgin and memory cells was found between CD4+ and CD8+ subsets. As expected, at birgh 95-99% of the CD3+ lymphocytes expressed the CD45RA isoform. A rapid increase of CD45R0+ cells was observed in the first 2-3 decades of life, this phenomenon being much more pronounced on CD4+ cells. Subsequently, the increase of the 'memory' compartment was much less rapid, so that in centenarians a consistent reservoire of CD45RA+ among CD4+ cells was still present (about 20%). In these exceptional individuals the percentage of CD45RA+ cells among CD8+ T lymphocytes was even higher (about 50%), and only slightly lower than that of young donors (about 55-60%). Thus, the main changes occurred at a different rate in CD4+ (about 20%). In these exceptional individuals the percentage of CD45RA+ cells among CD8+ T lymphocytes was even higher (about 50%), and only slightly lower than that of young donors (about 55-60%). Thus, the main changes occurred at a different rate in CD4+ and in CD8+ T cells, at an age of between 0 and 30 years, when the thymus is still functionally active. Interestingly, no difference in the usage of CD45 isoforms was observed within T cells bearing four different V beta-T cell receptor (TCR). The significance of this age-related unbalance is unknown. However, the presence of a great number of CD45RA+ T lymphocytes within the CD4+ and the CD8+ T cell subsets even in the peripheral blood of centenarians poses the problem of their origin (thymus? extrathymic sites?), of their functional role and of their lifespan. Moreover, the data on centenarians suggest that they may represent a very selected population where a slowing of immunosenescence occurs.

Use of flameless atomic absorption spectroscopy in immune cytolysis for nonradioactive determination of killer cell activity

We describe here a novel method to evaluate natural killer (NK) cytolytic activity by use of flameless atomic absorption spectroscopy (GF-AAS). This technique may be adopted for use in laboratories equipped with electrothermal atomic absorption spectrometers. Nonradioactive Cr as Na2CrO4 was used to label target cells (K562), and cell lysis was evaluated by measuring Cr released after 4 h of incubation with the effectors. We selected 520 micrograms/L as the optimal dose for labeling targets, between 12 and 20 h as the optimal incubation time, and 10(4) cells as the optimal target size. Advantages of this method include: (a) exclusion of radioactive tracer, with no risk for workers; (b) limited costs; (c) high sensitivity and reproducibility; (d) possibility to store samples; and (e) better control of Cr used for labeling cells due to well-determined, fixed Cr concentrations in the range of nontoxic and linear cellular uptake. Comparison with data obtained by conventional 51Cr labeling of targets killed by the same effectors was excellent, yielding comparable results and corroborating the method.

Use of flameless atomic absorption spectroscopy in immune cytolysis for nonradioactive determination of killer cell activity

We describe here a novel method to evaluate natural killer (NK) cytolytic activity by use of flameless atomic absorption spectroscopy (GF-AAS). This technique may be adopted for use in laboratories equipped with electrothermal atomic absorption spectrometers. Nonradioactive Cr as Na2CrO4 was used to label target cells (K562), and cell lysis was evaluated by measuring Cr released after 4 h of incubation with the effectors. We selected 520 micrograms/L as the optimal dose for labeling targets, between 12 and 20 h as the optimal incubation time, and 10(4) cells as the optimal target size. Advantages of this method include: (a) exclusion of radioactive tracer, with no risk for workers; (b) limited costs; (c) high sensitivity and reproducibility; (d) possibility to store samples; and (e) better control of Cr used for labeling cells due to well-determined, fixed Cr concentrations in the range of nontoxic and linear cellular uptake. Comparison with data obtained by conventional 51Cr labeling of targets killed by the same effectors was excellent, yielding comparable results and corroborating the method.

Functional heterogeneity of an isolated mitochondrial population revealed by cytofluorometric analysis at the single organelle level

Isolated rat liver mitochondria were incubated under various metabolic conditions to determine their membrane potential (MMP) as measured continuously by a tetraphenylphosphonium (TPP+)-selective electrode. By flow cytometry, a parallel analysis of fluorescence emissions observing single mitochondria stained with the lipophilic cation 5,5',6,6'-tetrachloro-1,1'3,3'-tetraethylbenzimidazolcarbocyanine iodide (JC-1) revealed linear correlation between the median orange fluorescence (FL2) due to J-aggregate formations and MMP values measured by TPP+. No correlation was detected with the green fluorescence (FL1) emission. A significantly higher correlation appeared between the FL2/FL1 ratio and MMP values. Within the same mitochondrial population, cytofluorimetric analysis revealed the presence of various classes of organelles with different MMP, whose distribution was dependent on metabolic condition. The highest functional heterogeneity was found in deenergized mitochondria, while the highest homogeneity was observed during the first phase of the phosphorylative process. Thus, these data suggest that the cytofluorimetric use of JC-1 provides direct experimental evidence for the hypothesis of functional mitochondrial heterogeneity, at least with respect to their membrane potential.

Control of apoptosis by the cellular ATP level

Apoptosis is a physiological form of cell death. Its causes and execution mechanisms are not clearly understood. Oxidative stress, nitric oxide and its congeners, Ca2+, proteases, nucleases, and mitochondria are considered mediators of apoptosis. At present their importance and exact role are elusive but it is clear that mitochondria are both the target and the source of oxidative stress, nitric oxide, and Ca2+. The mitochondrial membrane potential (delta psi), which is the driving force for mitochondrial ATP synthesis, declines during apoptosis, and maintenance of delta psi prevents apoptosis. Since apoptosis is highly regulated and involves the activity of hydrolytic enzymes, chromatin condensation and vesicle formation apoptosis is likely to have a high energy demand. We propose that the cellular ATP level is an important determinant for cell death. This hypothesis is supported by circumstantial evidence, is consistent with the available data, has a corrolary in aging, and is amenable to direct experimental testing particularly with flow cytometry as a promising tool.

Successful immunosenescence and the remodelling of immune responses with ageing

In recent decades, major theoretical and technological advances have been achieved in the field of immunology. These have allowed the scientific community to analyse the immune system in a much more sophisticated manner than was possible even 20 years ago. Moreover, great theoretical changes have also occurred in gerontology-in particular, the hypothesis has been put forward that ageing and diseases are two different phenomena, and that successful ageing, i.e. ageing in good psychophysical conditions, is really possible for most humans and animals. Immunosenescence was then carefully investigated, either in selected healthy people of advanced age or in the oldest old people, such as healthy centenarians. The main results showed that most immune parameters are indeed well preserved even at this far advanced age. This paper deals with some of the most important theoretical problems of immunosenescence. An immunological tenet was that the most important phenomenon of immunosenescence is the involution of the thymus. In most textbooks and papers it is taken for granted that the thymus starts its involution immediately after puberty. When people aged 60-65 were considered old, it was not difficult to think that they could live for the rest of their life with a fully involuted thymus. The findings on centenarians challenge this tenet, as they have only a small reduction of T lymphocytes, and a relatively normal number of virgin and memory T cells, together with a functional T cell repertoire. Other observations reported here on centenarians, concerning the activity of B lymphocytes and the cytokine network, as well as those on the well-preserved innate immunity and the cells' capability of undergoing proliferation after appropriate stimuli, suggest that complex immune changes occur with age, but also indicate that we have to modify our attitude, to grasp the new scenario which is emerging. Immunosenescence can no longer be considered as a unidirectional deterioration, and this complex phenomenon is much better described by terms such as 'remodelling', 'reshaping' or 'retuning'.

Prolactin increases the susceptibility of primary leukemia cells to NK and LAK effectors

Our previous studies have shown that prolactin (PRL), a pituitary and lymphocyte hormone and a ligand of the cytokine/hemopoietin receptors (R) superfamily, acts synergistically with interleukin (IL)-2 on the development of lymphokine activated killer (LAK) cells and enhances the effects of GM-CSF and IL-3 on myeloid progenitors' proliferation and differentiation. More recently, we have demonstrated that GM-CSF and IL-3 increase the sensitivity of acute myeloid leukemic (AML) cells to LAK activity. Together, these findings have prompted us to study the role of PRL on the target arm of the LAK response. We show here that CD33+ blasts from AML patients express membrane PRL-R and that the PRL/PRL-R interaction is followed by increased susceptibility to natural killer (NK) (p < 0.02) and LAK (p < 0.001) cells. As predicted from the dimerization model of PRL-R and in agreement with previous reports, the response of AML blasts to PRL was bell-shaped with a trend peak at 25 ng/ml. Although enhanced lysis occurred at the target recognition level, it was not accompanied by changes in the MHC class I, cellular adhesion molecules, or myeloid differentiation antigens. Cell cycle recruitment and lysis increased concurrently in three cases studied, suggesting a modulatory action of PRL on the expression of putative cycle-related NK/LAK-target structures. Together, these data strengthen the role of PRL in the LAK response.

Stress proteins in inflammation

Inflammation provides those searching in the field with a number of "models" allowing them to study, in vivo, in humans and in animals, the regulation and the functions of HSP, which are being considered as a new and promising marker for the severity and the prognosis of inflammatory diseases. HSP are differentially regulated according to the type of inflammation, whether acute or chronic, whether self-limiting (inflammatory cell elimination by apoptosis) or self-perpetuating (inflammatory cell death by necrosis). We propose that mitochondria are a key organelle in determining the outcome of inflammation, because they are both the cellular "switchboard" for apoptosis and a selective target for the protective effects of HSP against the cytotoxic effects of TNF alpha and ROS. On the other hand, HSP exert multiple protective effects in inflammation, including self/non-self discrimination, enhancement of immune responses, immune protection, thermotolerance and protection against the cytotoxicity of inflammatory mediators. The latter protective effects against the deleterious effects of the mediators of inflammation, including ROS and cytokines, open new avenues for the development of original anti-inflammatory therapies, such as non-toxic inducers of a complete HS response. It may well be that the "beneficial effects of fever" already described by Hippocrates actually relate to increased HSP expression during fever, and to their protective effects....

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.

Evidence for dissimilar mechanisms of enhancement of inorganic and organic hydroperoxide cytotoxicity by L-histidine

L-Histidine markedly increases inorganic and organic hydroperoxide-induced cytotoxicity and DNA single-strand breaks (SSBs) in Chinese hamster ovary cells. These effects were prevented by the iron chelator o-phenanthroline and were insensitive to the antioxidant N,N'-diphenyl-1,4-phenylenediamine. An excess of L-glutamine, a competitive inhibitor of L-histidine uptake, prevented the L-histidine-mediated enhancement of cytotoxicity induced by both inorganic and organic peroxides. L-Glutamine did not affect the level of DNA SSBs produced by H2O2/L-histidine, although it abolished the enhancement of SSB formation triggered by L-histidine in cells exposed to the organic peroxides. DNA SSBs generated by the organic hydroperoxides either alone or associated with L-histidine were removed with superimposable kinetics, whereas those produced by H2O2 in the presence of the amino acid were repaired more slowly than SSBs produced by the oxidant alone. DNA double-strand breaks, which are considered to be highly cytotoxic, were detected only in cells treated with H2O2 and L-histidine. Finally, L-histidine was shown to markedly increase the extent of mitochondrial damage produced by organic but not by inorganic hydroperoxides.

Autogeneic but not allogeneic earthworm effector coelomocytes kill the mammalian tumor cell target K562

Earthworm coelomocytes have been used as effector cells against the human tumor target, K562. To first assess the viability of effectors, incorporation of [3H]-thymidine was tested and was higher in autogeneic (A<==A, self) than in allogeneic (A<==>B, nonself) coelomocytes. A<==>A showed significantly greater numbers in S, G2, or M phases than A<==>B coelomocytes. When A<==>A or A<==>B were cultured, no significant cell killing occurred in either, as measured in a 4-hr 51Cr release assay. A<==>A but not A<==>B killed K562 target cells. Cytotoxicity was dependent upon membrane binding between small, electron-dense coelomocytes and targets; it was enhanced by adding PHA. The heat labile supernatant from A<==>A but not from A<==>B killed K562 targets after cultivation for 10 min at 22 degrees C, but not immediately after washing. Recognition of, binding to, and killing of foreign cells in a natural killer cell-like reaction may reflect natural immunity in earthworms.

The use of non-radioactive chromium as an alternative to 51Cr in NK assay

A novel method to measure target cell cytolysis based on the use of 'cold', non-radioactive chromium and on the determination of metal release by graphite furnace atomic absorption spectroscopy (FAAS) is proposed. Natural killer (NK) assays were performed by labelling target cells with chromium as Na2CrO4, and results were compared with those obtained by conventional overnight labelling with 51Cr of targets killed by the same effectors. The cytotoxic capacity of peripheral blood lymphocytes from healthy subjects was evaluated, and NK activity measured with both methods showed a good agreement at each of the tested effector to target cell ratios (between 100:1 and 1:1), with a high and significant coefficient of correlation (r = 0.931, p < 0.0001). The selection of the appropriate Cr concentrations for labelling target cells took into account both the sensitivity of our instrumentation and the possible toxic effects of the metal. A study of the effects of Cr on the cell line (K562) which is usually employed as a target in NK tests showed that Cr could have a detrimental effect on cellular function, with significant numbers of cells with depolarised mitochondria and reduced DNA synthesis after 24 h incubation using Cr levels higher than 15 mumol/l (780 micrograms/l). The method proposed here has a number of advantages, including the use of a non-radioactive tracer, limited costs, high sensitivity and reproducibility, and the possibility of storing samples. In addition, the technique uses a fixed Cr concentration which is known to be non toxic.

Involvement of CD45 in dexamethasone- and heat shock-induced apoptosis of rat thymocytes

CD45 is a transmembrane tyrosine-specific phosphatase which participates in lymphoid cell signal transduction during T cell activation, as well as in intrathymic negative and positive selection. In mammals, this molecule exhibits a variety of isoforms of different molecular weight, whose roles have still to be fully elucidated. We report here that apoptosis of rat thymocytes after in vitro dexamethasone and heat shock treatment was accompanied by an early significative increase of cells expressing CD45RC, the high molecular weight isoform of CD45 molecule. The same phenomenon was observed in thymocytes derived from in vivo dexamethasone-treated rats. However, the increase of CD45RC+ cells was not apparently characteristic of cells undergoing apoptosis, as the same phenomenon was also observed in rat thymocytes induced to proliferate by Concanavalin A. On the whole, these results suggest that CD45 modulation can be added to the list of early molecular events, such as the increased expression of genes (ornithine decarboxylase), proto-oncogenes (c-fos, c-jun, c-myc) and activation of transcription factors (AP-1, NFkB), we previously demonstrated in the same experimental model to occur and to be shared by these two apparently opposite biological processes, i.e., cell proliferation and apoptosis, both likely depending on a complex balance of protein phosphorylation and dephosphorylation.

Mitochondrial mass and membrane potential in coelomocytes from the earthworm Eisenia foetida: studies with fluorescent probes in single intact cells

Earthworm coelomocytes exist in two forms, i.e., small (SC) and large (LC) cells, as demonstrated by velocity sedimentation, electron microscopy, and FCM. However, we know little concerning the functional activities of various, important organelles, such as mitochondria. In comparison with SC, LC from Eisenia foetida have a higher number of mitochondria, and, accordingly, showed a greater fluorescence intensity when mitochondrial mass was measured by nonyl acridine orange and FCM. To measure MMP we used both the lipophilic cationic probe JC-1 and Rh123. The intracellular localization of JC-1 in SC and LC was observed by fluorescence microscopy. Using JC-1, MMP was analyzed separately on SC and LC by FCM, and significant percentages of coelomocytes (> 95% of SC and about 90% of LC) displayed a high MMP. Adding 0.1 microM VAL caused most SC to depolarize, while this occurred in only a few LC. Rh123 gave different results: no effects of VAL were observed either in SC or in LC. In coelomocytes there may be several energy-independent Rh123-binding sites whose role must still be elucidated. On the whole, these data indicate that it is possible to analyze mitochondrial parameters by FCM in intact invertebrate coelomocytes, and that the type of cell and the probe used have a critical importance.

Protective effect of N-acetylcysteine in tumor necrosis factor-alpha-induced apoptosis in U937 cells: the role of mitochondria

The existence of two different pathways for cell death has been postulated. In addition to the passive and traumatic process leading to necrosis, an active program characterized by organelle integrity and called apoptosis has been described. A positive correlation between the apoptotic cell death process and oxidative imbalance has been demonstrated. In fact, the antioxidant N-acetylcysteine (NAC) seems to be capable of impairing the apoptotic program, replenishing intracellular reduced glutathione content in cells exposed to tumor necrosis factor-alpha (TNF) as apoptotic inducer. Moreover, protein synthesis inhibitors such as cycloheximide (CHX) can facilitate apoptotic triggering by TNF, and mitochondrial function was suggested to be essential in the TNF-mediated apoptotic process. With this in mind, a specific analysis using the JC-1 probe, a fluorescent dye which is capable of indicating mitochondrial membrane potential (delta psi m) changes, was carried out. Our results show that TNF exposure is capable of altering the mitochondria and that NAC protection from CHX + TNF-induced apoptosis could be due to a direct effect of the drug on mitochondrial integrity and function.