Laboratory-based diagnosis of pneumococcal pneumonia: state of the art and unmet needs.

In view of the increasing use of pneumococcal vaccines, especially in the developing world, there is a need for appropriate diagnostics to understand the aetiology of pneumonia, to define the burden of pneumococcal disease, and to monitor vaccine efficacy and effectiveness. This article summarizes a meeting on the diagnosis, detection and serotyping of pneumococcal disease organized by PATH and Fondation Mérieux (18-20 October 2009, Fondation Mérieux Conference Centre, Les Pensières, France). Workers and experts met to discuss the gaps in the microbiology-based diagnosis of Streptococcus pneumoniae disease, with special emphasis on pneumonia. The meeting was designed to evaluate the state of the art of pneumococcal diagnostics and serotyping methodologies, identify research and development needs, and propose new guidelines to public health authorities to support the introduction of vaccines. Regarding detection, the main recommendations were to encourage chest X-rays and antigen detection in urine. Large-scale studies are needed to evaluate the diagnostic utility of test algorithms that associate chest X-rays, antigen detection in urine, S. pneumoniae quantitative PCR in nasopharyngeal aspirates and sputum, and C-reactive protein or procalcitonin measurement in blood. Efforts should be focused on proteomics to identify pneumococcus-specific antigens in urine or host markers in blood expressed during pneumonia. It was recommended to develop S. pneumoniae typing capacities, to understand the epidemiology of pneumococcal disease, and to evaluate vaccine effectiveness. Simple and effective approaches are encouraged, and new technologies based on beads, microarrays or deep sequencing should be developed to determine, in a single test capsular serotype, resistance profile and genotype.

A caspase-independent pathway of MHC class II antigen-mediated apoptosis of human B lymphocytes.

MHC class II molecules have a crucial role in thymic selection and in generating Ag-specific T cell responses. There is extensive evidence for second messenger generation via MHC class II molecules, which can lead to apoptosis of B lymphocytes. We have examined HLA class II-mediated apoptosis in both normal and tumoral human B lymphocytes. Phosphatidylserine exposure and DNA fragmentation were observed in B cells within 24 h of stimulation via HLA class II. In marked comparison with Fas, the cell-permeable and irreversible caspase inhibitors zVAD-fmk and DEVD-fmk failed to inhibit HLA-DR-mediated apoptosis. No direct activation of caspase 3 was detected, and cleavage of pro-caspase 3 was not observed. Cleavage of poly(ADP-ribose) polymerase was detected via Fas but not via HLA class II. Although phosphatidylinositol-3-kinase has been implicated in HLA class I-mediated apoptosis, neither wortmannin nor LY294002 affected HLA class II-mediated apoptosis. CD95-sensitive cells were used to reveal that death occurred independently of CD95-CD95 ligand interactions. Overall, these data reveal a pathway of HLA-DR-mediated apoptosis that neither requires nor involves caspases. Moreover, it is phosphatidylinositol-3-kinase independent and Fas/CD95 independent. This pathway of HLA class II-mediated apoptosis could have an important role in the regulation of APC populations or in the control of malignant B lymphocyte proliferations.

Human skeletal muscle cytosols are refractory to cytochrome c-dependent activation of type-II caspases and lack APAF-1.

Apoptotic regulatory mechanisms in skeletal muscle have not been revealed. This is despite indications that remnant apoptotic events are detected following exercise, muscle injury and the progression of dystrophinopathies. The recent elicitation of a cytochrome c-mediated induction of caspases has led to speculation regarding a cytochrome c mechanism in muscle. We demonstrate that cytosols from skeletal muscle biopsies from healthy human volunteers lack the ability to activate type-II caspases by a cytochrome c-mediated pathway despite the confirmed presence of both procaspase-3 and -9. This was not due to the presence of an endogenous inhibitor, as the muscle cytosols enhanced caspase activity when added to a control cytosol, subsequently activated by cytochrome c and dATP. In addition, we demonstrate that muscle cytosols lack the apoptosis protease activator protein-1 (APAF-1), both at the protein and mRNA levels. These data indicate that human skeletal muscle cells will be refractory to mitochondrial-mediated events leading to apoptosis and thus can escape a major pro-apoptotic regulatory mechanism. This may reflect an evolutionary adaptation of cell survival in the presence of the profusion of mitochondria required for energy generation in motility.

Importance of the redox state of cytochrome c during caspase activation in cytosolic extracts.

The export of cytochrome c from mitochondria to the cytoplasm has been detected during apoptosis. Addition of cytochrome c to cytosolic extracts can activate the caspases, suggesting that this export could be an important intracellular signal for initiating the apoptotic programme. We have investigated the mechanism of caspase activation by cytochrome c. Mitochondrial cytochrome c normally shuttles electrons between complexes III and IV of the electron transport chain. Interaction with these complexes is dependent on electrostatic interactions via a polylysine binding pocket. Cytosolic caspase activation was only observed with intact holocytochrome c, and increasing the ionic composition of the extracts prevented activation, suggesting that stringent allosteric interactions between cytochrome c and other cytoplasmic factors are necessary. Cytochrome c was fully reduced within 5 min of addition to the cytosolic extracts. Potassium ferricyanide could maintain cytochrome c in an oxidized state, but care was taken to use ferricyanide at concentrations where its polyanion effect did not cause interference. The oxidized form of cytochrome c was able to activate the caspases. We conclude that reduced cytochrome c will function in the cytoplasm; however, its reduction is not a critical step, and electron transfer from cytochrome c to its cytoplasmic-binding partner(s) is not necessary in the pathway leading to apoptosis.

Mechanism of dithiocarbamate inhibition of apoptosis: thiol oxidation by dithiocarbamate disulfides directly inhibits processing of the caspase-3 proenzyme.

Dithiocarbamates (DCs) have been reported to be potent inhibitors of apoptosis in several different model systems, which suggests a target common to the apoptotic machinery. Without further investigation, this has been assumed to reflect an antioxidant activity of the DCs. However, we have recently shown that DCs exert prooxidant effects on T cells [Nobel et al. (1995) J. Biol. Chem. 270, 26202-26208], which are dependent on their transfer of external copper into the cells and can be inhibited by the inclusion of high-affinity external copper chelators in the medium. Investigating antiapoptotic actions of DCs, we found that inclusion of a membrane-impermeable copper chelator severely compromised the inhibitory activity of reduced DCs. Since copper can promote DC oxidation to the respective DC disulfides, the inhibitory effect on lymphocyte apoptosis might be mediated by the DC disulfides. In agreement with this we observed that DC disulfides were more potent inhibitors of T cell apoptosis than their reduced counterparts. Inhibition of apoptosis by DC disulfides correlated with the inhibition of caspase-3 proenzyme processing and activation. Similar results were obtained in a cell-free model system of caspase-3 activation. Significantly, dithiothreitol reduction of the DC disulfide abolished its inhibition of in vitro proenzyme processing, thereby demonstrating thiol-disulfide exchange between the DC disulfide and a free thiol group on an activator(s) of caspase-3. Since T cell apoptosis involves the generation of mature caspase-3 and requires caspase-3-like activity, we propose that (1) DC disulfides are the active agents behind DC inhibition of apoptosis and (2) their site of action is the proteolytic activation of this enzyme. These findings also reveal the potential for other thiol-oxidizing toxicants to inhibit apoptosis by preventing the proteolytic activation of caspases.

Involvement of cellular proteolytic machinery in apoptosis.

Programmed cell death (PCD), a genetically controlled cell deletion process, plays an important role in the regulation of cellular and tissue homeostasis. The requisite for proteolysis during PCD-induced apoptosis is well documented. The cellular proteolytic machinery includes numerous proteases localized in membranes, cytoplasm, and nucleus. This machinery may function to remove denatured or misfolded protein from the cytoplasm on a routine basis and may also cleave proteins thereby implementing their activation. The well established role of some proteases is to maintain fundamental cellular processes; however, the precise cellular location and function of other proteases which make a contribution to a unique unidirectional process such as apoptosis remains unclear. The functional overlap between 'scheduled' and 'unscheduled' proteolysis may potentially lead to confusion in this research area. In this review we will discuss certain cellular proteolytic systems and highlight the possible involvement of each in apoptosis.

Proteases in Fas-mediated apoptosis.

Involvement of a unique family of cysteine proteases in the multistep apoptotic process has been documented. Cloning of several mammalian genes identifies some components of this cellular response. However, it is currently unclear which protease plays a role as a signal and/or effector of apoptosis. We summarize contributions to the data concerning proteases in Fas-mediated apoptosis.

The role of proteolysis in T cell apoptosis triggered by chelation of intracellular Zn2+.

Our previous work showed that chelation of intracellular Zn2+ with N,N,N',N'-tetrakis (2-pyridylmethyl) ethylenediamine (TPEN) induces apoptosis in rat thymocytes. The molecular mechanism involved in TPEN-triggered apoptosis remains unknown, except that it is a Ca2+-independent process. In the present study, we show that TPEN is unable to induce DNA fragmentation when added to isolated thymocyte nuclei, indicating that activation of a cytoplasmic component is essential for TPEN-induced apoptosis. Since cytosolic proteases related to interleukin-1beta-converting enzyme (ICE) are implicated as key activators of apoptosis in many different systems, we investigated the possible involvement of such proteases in TPEN-induced apoptosis. We found that treatment of thymocytes with TPEN caused an early degradation of nuclear poly(ADP-ribose) polymerase (PARP) and lamin prior to DNA cleavage. This could be inhibited by Z-Val-Ala-Asp-chloromethylketone (VADcmk), an inhibitor of ICE-like proteases, but not by an inhibitor of Ca2+-regulated serine protease. Jurkat T cells also underwent extensive DNA fragmentation when incubated with TPEN. A cytosolic fraction, prepared from TPEN-treated Jurkat cells, produced extensive DNA fragmentation when applied to isolated thymocyte nuclei, whereas the cytoplasmic extract from untreated cells was ineffective either alone or together with TPEN. The apoptosis-inducing activity in cytosolic fraction from TPEN-treated Jurkat cells was blocked by incubating cells in the presence of VADcmk or another inhibitor of ICE-like proteases, Ac - Asp - Glu - Val - Asp-aldehyde (DEVD-CHO), which has been found to competitively inhibit CPP32/apopain. An increase in enzyme activity that cleaves Ac-Asp-Glu-Val-Asp-7-amino-4-methylcoumarin (DEVD-AMC), a fluorogenic substrate of CPP32/apopain and Mch3alpha, was detected in TPEN-treated thymocytes and Jurkat cells. In addition, the proteolytic cleavage of CPP32 resulting in the formation of two active fragments (p17 and p12) was observed in cytosolic extracts from TPEN-treated Jurkat cells, but not in extracts which were prepared from cells treated with TPEN in the presence of VADcmk or DEVD-CHO. Our results suggest that activation of cytosolic ICE-like proteases is an essential step in TPEN-induced apoptosis, and that CPP32/apopain is critically involved in this process.

Protease involvement in fodrin cleavage and phosphatidylserine exposure in apoptosis.

A detailed kinetic analysis of three extranuclear end points of apoptosis, phosphatidylserine exposure, alpha-fodrin degradation, and plasma membrane blebbing, was performed and compared with nuclear fragmentation and the activation of the interleukin-1beta-converting enzyme (ICE)-like proteases in Jurkat T lymphocytes stimulated by anti-Fas monoclonal antibody (anti-Fas mAb) and in monocytic U937 cells stimulated by tumor necrosis factor (TNF) and cycloheximide. Phosphatidylserine exposure was quantitated by plasma clotting time, as well as annexin V-fluorescein isothiocyanate binding, and the ICE-like protease activity was examined by the cleavage of a specific fluorogenic peptide substrate Ac-Asp-Glu-Val-Asp-amino-4-methylcoumarin. VAD-chloromethylketone (VAD-cmk), an inhibitor of ICE-like proteases, effectively inhibited ICE-like activity in both cell types studied, whereas the calpain inhibitor calpeptin was ineffective. VAD-cmk also effectively inhibited all three extranuclear events, as well as nuclear fragmentation, in Jurkat cells stimulated by anti-Fas monoclonal antibody, indicating that ICE-like proteases play an important role in the regulation of this apoptotic system. Calpain inhibitors were ineffective in this system. TNF-induced extranuclear and nuclear changes in U937 cells were inhibited by calpeptin but were not as effectively inhibited by VAD-cmk as in Jurkat cells. This suggests that ICE-like enzymes predominate in anti-Fas monoclonal antibody-stimulated Jurkat cells, whereas proteases affected by calpain inhibitors as well as the ICE-like enzymes are involved in the signaling of apoptotic events in TNF-induced U937 cells. Importantly, the two apoptotic systems seem to be regulated by different proteases.

Proteases in apoptosis.

The interleukin-1 beta-converting enzyme (ICE)-like family proteases have recently been identified as key enzymes in apoptotic cell death. Among these proteases one can identify specific activities which may be involved in cytokine production or in resident protein cleavage. Several factors influence the constitutive apoptotic mechanism and may provide insight into the role of protease(s) in apoptosis. Although it appears that ICE family members play a most important role in promoting apoptotic cell death, evidence has been advanced that other proteases are also involved in sequential or parallel steps of apoptosis. Activation of a particular protease can lead to processing molecules either of the same or different proteases, leading to an activation of a protease cascade. Here we attempt to summarize the current thinking concerning these proteases and their involvement in apoptosis.

Antigen-presenting B cells: efficient uptake and presentation by activated B cells for induction of cytotoxic T lymphocytes against vesicular stomatitis virus.

We have evaluated the efficacy of mitogen (LPS/DxSO4)-activated B cells (B lymphoblasts) to function as antigen-presenting cells (APC) for vesicular stomatitis virus (VSV). Our studies revealed that B lymphoblasts induced potent cytotoxic thymus (T)-derived lymphocyte (CTL) activity in VSV-immune splenic T cells depleted of adherent accessory cells. Dose-response curves indicated that B lymphoblasts were approximately 15-20 times more efficient APC than spleen cells for CTL induction against VSV. There was little evidence of reprocessing of viral antigens by the responder population because only CTL activity restricted to the parental haplotype of the B lymphoblast was generated following stimulation of VSV-immune F1 T cells. B lymphoblasts activated VSV-specific memory CTL which expressed the Lyt-1-23+, AsGM1+ phenotype without activating natural killer and/or lymphokine-activated killer cells. The ability of B lymphoblasts to function as efficient APC was not related to enhanced viral replication in these cells because potent VSV-specific proliferative and class I-restricted CTL responses were induced by B lymphoblasts infected with VSV rendered noninfectious by exposure to ultraviolet (uv) light. This indicates that activated B cells can efficiently process and present input virion protein. Purified splenic B cells that were not activated by mitogen stimulation did not function as APC for VSV even at high multiplicities of infection. The failure of B cells to function as APC for VSV was related to inefficient uptake of VSV and their inability to provide accessory cell signals required for T-cell proliferation; both these functions developed following mitogen stimulation. These data suggest that activated B cells may function as a potent APC population for virus independent of the specificity of their immunoglobulin antigen receptor.

Cadmium-induced suppression of the primary immune response and acute toxicity in mice: differential interaction of zinc.

Four groups of 6-week-old C3H mice were injected sc with either sterile saline, 2.8 mg Cd/kg body weight, 2.8 mg Zn/kg body weight, or 2.8 mg each of Cd and Zn/kg body weight. Forty-eight hours after the initial injection, all mice received a second dose of their respective treatments plus an iv injection of sheep red blood cells. On Days 2, 3, 4, and 5 postimmunization the mice were killed. Spleen cells were used in a hemolytic plaque-forming assay for the quantitation of the primary humoral response. Although the combined administration of zinc and cadmium completely prevented the fatal effects of the cadmium (0 vs 55% mortality), zinc failed to alleviate the cadmium-induced inhibition of the humoral response.

Iron retention and excretion in mice transfused with homologous or heterologous blood and treated with chelators.

The studies in this report characterized an animal model for detecting chemicals that are capable of depleting elevated tissue iron. Male mice were transfused with heated, washed erythrocytes and the iron uptake by liver and spleen plus urinary iron excretion were measured. After the time and transfusion iron accumulations and excretion patterns were established, the influence of the following experimental variables was examined and compared: homologous vs heterologous blood transfusion, dose related responses, the efficacy of a chelator against iron buildup from long-term transfusion, and organ iron responses to an agent with combined chelation and hemolytic potentials. Both the liver and the spleen accumulated iron from transfused blood; however, the spleen appeared to have a limited capacity compared to the liver. Drugs having lower potencies or given at lower dose levels enhanced urinary iron excretion. Higher potencies or higher dose levels induced the same response and depleted liver iron. At still higher doses or with more potent drugs, the two responses mentioned occurred accompanied by spleen iron reduction. An increased urine iron alone was equivocal since drug-induced hemolytic anemia caused a ferricosuria accompanied by elevated liver and spleen iron. Heterologous or homologous transfusions produced similar organ iron elevations and urine iron excretion in untreated mice. A higher level of drug potency was required to deplete tissue iron whenever the drug treatment was administered following transfusion.