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Group B streptococci (GBS) are an important cause of neonatal sepsis, pneumonia and meningitis. In the early phase of infection, macrophages and polymorphonuclear cells (PMN) are the first immune cells that interact with GBS. In this in vitro study, to gain insight into GBS-macrophage interaction in the absence of type-specific antibodies, we examined the features of GBS survival in thioglycollate-elicited murine peritoneal macrophages and the effect of GBS on the protein kinase C (PKC)-dependent transduction pathway. Our results demonstrate that type Ia GBS, strain 090 (GBS-Ia) and type III GBS strain COH 31r/s (GBS-III), after in vitro phagocytosis survive and persist intracellularly in macrophages for up to 24 and 48 hr, respectively. However, macrophage activation by interferon-gamma (IFN-gamma) and lipopolysaccharide from Escherichia coli (LPS) caused a significant reduction in the time of intracellular persistence. Macrophage activation by IFN-gamma and LPS seems to be a multifactorial event involving multiple intracellular signal pathways also including PKC. Since PKC is one of the components in the signal network leading to macrophage activation and an important target for several intracellular micro-organisms, we wondered whether PKC could have a role in intracellular GBS survival. Both PKC depletion by treatment with phorbol 12-myristate 13-acetate (PMA) for 18 hr and PKC inhibition by Calphostin C rendered macrophages more permissive for the intracellular GBS survival. Furthermore, GBS-infected macrophages were unable to respond to PMA and LPS, activators of PKC, by inducing antimicrobial activity. The ability of GBS to impair PKC-dependent cell signalling was also demonstrated by the reduced c-fos gene expression in GBS-infected macrophages with respect to control macrophages, after LPS stimulation. In conclusion, our results indicate that GBS survive in macrophages and impairment of PKC signal transduction contributes to their intracellular survival.

Alterations in Notch signaling are involved in chronic lymphocytic leukemia (CLL) pathogenesis, a hematological disease characterized by the accumulation of CD19+/CD5+ B cells resistant to apoptosis. We previously reported that constitutive Notch1/2 activation contributes to apoptosis resistance of CLL cells.1 Furthermore, a NOTCH1 PEST domain mutation, resulting in a truncated protein more stable and active than wild-type (WT) protein, has recently emerged as a recurrent genetic lesion in CLL patients with adverse prognosis and poor outcome.2, 3 Despite the progress achieved on the role of NOTCH1 mutations in CLL outcome, little is known regarding their role in CLL cell biology. There is evidence that NOTCH1 mutation stabilizes Notch1 signaling in CLL cells,4 but the molecular mechanisms underlying this effect remain to be defined.

γ-Secretase inhibitors (GSIs) have been proposed for combined therapies of malignancies with a dysregulated Notch signaling. GSI I (Z-Leu-Leu-Nle-CHO) induces apoptosis of some tumor cells by inhibiting proteasome and Notch activity. Alterations in these two cell survival regulators contribute to apoptosis resistance of chronic lymphocytic leukemia (CLL) cells. Here, we investigated the mechanisms whereby GSI I increases apoptosis of primary CLL cells. Time-course studies indicate that initial apoptotic events are inhibition of proteasome activity, concomitant with an increased endoplasmic reticulum (ER) stress apoptotic signaling, and a consistent Noxa protein up-regulation. These events precede, and some of them contribute to, mitochondrial alterations, which occur notwithstanding Mcl-1 accumulation induced by GSI I. In CLL cells, GSI I inhibits Notch1 and Notch2 activation only in the late apoptotic phases, suggesting that this event does not initiate CLL cell apoptosis. However, Notch inhibition may contribute to amplify GSI I-induced CLL cell apoptosis, given that Notch activation sustains the survival of these cells, as demonstrated by the evidence that both Notch1 and Notch2 down-regulation by small-interfering RNA accelerates spontaneous CLL cell apoptosis. Overall, our results show that GSI I triggers CLL cell apoptosis by inhibiting proteasome activity and enhancing ER stress, and amplifies it by blocking Notch activation. These findings suggest the potential relevance of simultaneously targeting these three important apoptosis regulators as a novel therapeutic strategy for CLL.

A better understanding of apoptotic signaling in B-chronic lymphocytic leukemia (B-CLL) cells may help to define new therapeutic strategies. This study investigated endoplasmic reticulum (ER) stress signaling in spontaneous apoptosis of B-CLL cells and whether manipulating ER stress increases their apoptosis. Results show that a novel ER stress-triggered caspase cascade, initiated by caspase-4 and involving caspase-8 and -3, plays an important role in spontaneous B-CLL cell apoptosis. ER stress-induced apoptosis in B-CLL cells also involves CHOP/GADD153 up-regulation, increased JNK1/2 phosphorylation, and caspase-8–mediated cleavage of Bap31 to Bap20, known to propagate apoptotic signals from ER to mitochondria. In ex vivo B-CLL cells, some apoptotic events associated with mitochondrial pathway also occur, including mitochondrial cytochrome c release and caspase-9 processing. However, pharmacologic inhibition studies show that caspase-9 plays a minor role in B-CLL cell apoptosis. ER stress also triggers survival signals in B-CLL cells by increasing BiP/GRP78 expression. Manipulating ER signaling by siRNA down-regulation of BiP/GRP78 or treating B-CLL cells with 2 well-known ER stress-inducers, tunicamycin and thapsigargin, increases their apoptosis. Overall, our findings show that ER triggers an essential pathway for B-CLL cell apoptosis and suggest that genetic and pharmacologic manipulation of ER signaling could represent an important therapeutic strategy.

Notch signaling is involved in tumorigenesis, but its role in B–chronic lymphocytic leukemia (B-CLL) pathogenesis is not completely defined. This study examined the expression and activation of Notch receptors in B-CLL cells and the role of Notch signaling in sustaining the survival of these cells. Our results show that B-CLL cells but not normal B cells constitutively express Notch1 and Notch2 proteins as well as their ligands Jagged1 and Jagged2. Notch signaling is constitutively activated in B-CLL cells, and its activation is further increased in B-CLL cells, which resist spontaneous apoptosis after 24-hour ex vivo culture. Notch stimulation by a soluble Jagged1 ligand increases B-CLL cell survival and is accompanied by increased nuclear factor–kappa B (NF-κB) activity and cellular inhibitor of apoptosis protein 2 (c-IAP2) and X-linked inhibitor of apoptosis protein (XIAP) expression. In contrast, Notch-signaling inhibition by the γ-secretase inhibitor I (GSI; z-Leu-Leu-Nle-CHO) and the specific Notch2 down-regulation by small-interfering RNA accelerate spontaneous B-CLL cell apoptosis. Apoptotic activity of GSI is accompanied by reduction of NF-κB activity and c-IAP2 and XIAP expression. Overall, our findings show that Notch signaling plays a critical role in B-CLL cell survival and apoptosis resistance and suggest that it could be a novel potential therapeutic target.

Tumor necrosis factor alpha (TNFalpha) is constitutively produced by B-chronic lymphocytic leukemia (B-CLL) cells and may act as an autocrine factor for their growth and survival. However, very few data are available on the possible cytotoxic effect of TNFalpha produced by B-CLL cells. This study investigated whether B-CLL cells exert in vitro cytotoxicity by TNFalpha and if so, whether this cytotoxicity can be modulated by cytokines. In 8 of 12 patients (66.6%), B-CLL cells in vitro constitutively produced TNFalpha and exerted a TNFalpha-mediated cytotoxicity, evaluated in an 18-h 51Cr release assay, against the TNFalpha-sensitive Jurkat, U937 and K562 cell lines but not against the TNFalpha-resistant Raji cell line. Involvement of TNFalpha in B-CLL cell cytotoxicity is demonstrated by the fact that anti-TNFalpha antibodies strongly inhibited it and supernatants of cytotoxic cultures contained TNFalpha and mediated a completely TNFalpha-dependent cytotoxicity. When the cytotoxic B-CLL cells were stimulated with interleukin (IL)-2 plus IL-12, there was increased TNFalpha mRNA expression, TNFalpha production and TNFalpha-mediated cytotoxicity. All eight patients with cytotoxic leukemic cells had progressive disease and six of these also expressed high levels of ZAP-70 protein. In the other four patients (33.3%), B-CLL cells did not produce TNFalpha in vitro and were not cytotoxic, either spontaneously or after IL-2 plus IL-12 stimulation. Of these four patients, three had stable disease and one had progressive disease. The patient with progressive disease and one of the three with stable disease expressed low levels of ZAP-70 protein. We conclude that a group of B-CLL patients with progressive disease have leukemic B cells able to exert in vitro a TNFalpha-mediated cytotoxicity, which is modulated by cytokines.

Thiols are important molecules to control apoptosis. This study examined the effect of N-acetyl-L-cysteine (NAC) on in vitro spontaneous apoptosis of human tonsillar B lymphocytes (TBL). Results show that NAC inhibits TBL apoptosis and maintains their survival in vitro. The antiapoptotic action of NAC is progressively reduced when its addition to culture is delayed, is reversible, and is not blocked by cycloheximide. The antiapoptotic activity of NAC is associated with its ability to inhibit caspase-3 and -7 proteolytic processing, DNA-fragmentation factor 45 cleavage, and DNA fragmentation. Furthermore, NAC inhibits BID cleavage and cytochrome c release from mitochondria and increases the expression of Bcl-2 and BclXL survival proteins. However, it has no effect on caspase-9 cleavage and increases that of caspase-8 and poly(adenosine 5′-diphosphate-ribose)polymerase. We conclude that NAC-induced inhibition of TBL apoptosis is associated with inhibition of caspase-3 and -7 processing and is accompanied by changes in several regulatory components of the apoptotic process. These results pose the question of whether microenvironment thiols may in part contribute to in vivo B cell survival.

Meropenem, a new carbapenem antibiotic, was assessed to evaluate its effects on some functional parameters of human polymorphonuclear (PMN) and natural killer (NK) cells in comparison with imipenem/cilastatin. Both drugs significantly inhibited PMN phagocytosis and chemotaxis at concentrations of 2,000 and 4,000 μg/ml. They affected PMN microbicidal activity, evaluated against Candida albicans, only at 4,000 μg/ml. A study of the effects of both drugs on peripheral NK populations and the human NK line (NK-92) showed that even at 4,000 μg/ml there was no effect on antitumor activity. These data indicate that meropenem can reduce some PMN antimicrobial functions only at very high concentrations like imipenem/cilastatin, whereas no concentration influenced NK activity.

Inactivated Candida albicans (CA) cells induce strong activation of natural cytotoxic effectors in mice. In the present study we examined the expression of cytokine genes involved in the immune response to CA. It has been reported that differential cytokine production by natural immune cells is important for regulating the development of specific TH response. Northern blot analysis was performed on peritoneal exudate cells (PEC) recovered from CD2F1 mice injected ip with five doses of CA (CA-5d, on Days -14, -10, -7, -3, 0 with respect to the in vitro assays at 2, 24, and 72 hr) or from mice injected ip with four doses of CA (CA-4d, on Days -14, -10, -7, -3 with respect to the in vitro assay on Day 0). On Day 0, before the fifth CA injection, PEC expressed a high level of IL-2 and a low level of IL-1 beta mRNAs while genes coding for IL-4, IL-5, IL-6, IL-10, IL-12, TNF alpha, and IFN gamma were not expressed and there was a high level of NK activity. Two hours after CA-5d a high level of IFN gamma and a low level of IL-10 mRNAs were already evident, while IL-2 and much more IL-1 beta had greatly increased. IL-6, TNF alpha, and IL-2R alpha chain mRNAs were also detectable, whereas IL-4, IL-5, and IL-12 were not expressed. IL-12 mRNA was also absent in earlier stages of the CA sensitization. Both cellularity and NK activity of peritoneal exudate had increased with respect to Day 0. At 24 hr whereas IL-2 mRNA remained high, both IL-1 beta and IFN gamma mRNAs expression had decreased. Expression of other cytokines was no longer detectable but NK activity remained high and a significant LAK activity was also induced. After 72 hr, while the IL-2 mRNA level and NK activity were still high the IL-1 beta mRNA expression had further decreased. These results indicate that CA induces a predominant production of IFN gamma and IL-2, cytokines involved in the development of TH1 response but it is unable to induce IL-12. This secondary pathway, without IL-12 involvement in the development of TH1 response, is probably the result of the ability of IL-2, IL-1 beta, and TNF alpha to synergize in inducing IFN gamma synthesis by NK cells.

Recent evidence suggests that after repeated stimulations with inactivated C. albicans (CA) cells, CD2F1 mice respond with a cytokine pattern typical of T-helper 1 (ThI) subset development. The purpose of this study was to analyse the sequence of immunological events which, soon after priming mice with CA, lead to the development of primary and anamnestic response. A comprehensive kinetics analysis of cytokine mRNA expression was performed by Northern blot assay, in peritoneal exudate cells (PEC), at different phases of immune response to CA: after priming (one i.p. injection of 2 x 10(7) CA cells mouse), during development of the primary immune response (five progressive CA i.p. injections over a 2-week period) and in the anamnestic response (CA booster 30 days after the primary response). In vitro assays were performed 2 and 24 hr after every CA stimulation. The response to CA priming was characterized by an early and high expression of interleukin-2 (IL-2) and IL-1 beta mRNAs At 24hr. IL-2 mRNA was still at a high level, while IL-1 beta had greatly decreased. A weak expression of IL-10 was only induced at 2 hr. whereas IL-12 p40 subunit, interferon-7 (IFN-7) IL-4 and IL-5 mRNAs were undetectable. In this phase no in vitro proliferative response of PEC to CA was observed, whereas a significant natural killer (NK) activity was induced. From the second CA injection, the IFN-7 mRNA was already induced at 2 hr. Its expression level increased progressively with the number of CA injections persisting up to 24 hr after the fifth stimulation. A progressive increase of IL-2 mRNA expression was also induced whereas IL-1 beta and IL-10 mRNAs were always transiently expressed at 2 hr at levels similar to those observed after the priming. IL-12 p40 subunit. IL-4 and IL-5 mRNAs were never detectable. The expression of this selected cytokine pattern typical of Thl response was correlated with the development of CA-specific T lymphocytes as confirmed by the in vitro proliferative response of CA-5d-induced PEC to CA. NK activity also increased progressively with the number of CA injections and after the fifth stimulation lymphokine-activated killer (LAK) activity was also induced. The anamnestic response to CA was characterized by a very quick induction of high levels of IL-2, II N-gamma and IL-1 beta mRNAs. IL-2 and IFN-gamma mRNAs remained high up to 24 hr while IL-1 beta mRNA decreased strongly. A weak, transient expression of IL-10 mRNA was induced at 2 hr whereas the IL-12 p40 subunit, IL-4 and IL-5 mRNAs were not detectable. The presence of CA-specific memory lymphocytes was confirmed by the in vitro specific proliferative response of PEC to CA. CA booster caused also a very rapid and high level of NK/LAK activation. In conclusion, these results indicate that CA is able to progressively trigger differential on of the Th1 subset which develops in the absence of IL-12, and that Th memory cells retain the same selected Th1 cytokine profile developed in the primary immune response.

It has been shown that lysosomes are involved in B cell apoptosis but lysosomal glycohydrolases have never been investigated during this event. In this study we determined the enzymatic activities of some lysosomal glycohydrolases in human tonsil B lymphocytes (TBL) undergoing in vitro spontaneous apoptosis. Fluorimetric methods were used to evaluate the activities of beta-hexosaminidases, alpha-mannosidase, beta-mannosidase, alpha-galactosidase, beta-glucuronidase and alpha-fucosidase. Results show that in TBL during spontaneous apoptosis, there is a significant increase in the activity of beta-hexosaminidases, alpha-mannosidase, beta-mannosidase and beta-galactosidase. Also beta-glucuronidase and alpha-fucosidase activities increase but not in a significant manner. Further studies on beta-hexosaminidases revealed that also mRNA expression of the alpha- and beta-subunits, which constitute these enzymes, increases during spontaneous TBL apoptosis. When TBL are protected from apoptosis by the thiol molecule N-acetyl-L-cysteine (NAC), there is no longer any increase in glycohydrolase activities and mRNA expression of beta-hexosaminidase alpha- and beta-subunits. This study demonstrates for the first time that the activities and expression of some lysosomal glycohydrolases are enhanced in TBL during spontaneous apoptosis and that these increases are prevented when TBL apoptosis is inhibited.

Group B Streptococcus (GBS) is a pathogen that has developed some strategies to resist host immune defenses. Because phagocytic killing is an important pathogenetic mechanism for bacteria, we investigated whether GBS induces apoptosis in murine macrophages. GBS type III strain COH31 r/s (GBS-III) first causes a defect in cell membrane permeability, then at 24 h, apoptosis. Apoptosis was confirmed by several techniques based on morphological changes and DNA fragmentation. Cytochalasin D does not affect apoptosis, suggesting that GBS-III needs not be within the macrophage cytoplasm to promote apoptosis. Inhibition of host protein synthesis prevents apoptosis, whereas inhibition of caspase-1 or -3, does not. Therefore, GBS can trigger an apoptotic pathway independent of caspase-1 and -3, but dependent on protein synthesis. Inhibition of apoptosis by EGTA and PMA, and enhancement of apoptosis by calphostin C and GF109203X suggests that an increase in the cytosolic calcium level and protein kinase C activity status are important in GBS-induced apoptosis. Neither alteration of plasma membrane permeability nor apoptosis were induced by GBS grown in conditions impeding hemolysin expression or when we used dipalmitoylphosphatidylcholine, which inhibited GBS β-hemolytic activity, suggesting that GBS β-hemolysin could be involved in apoptosis. β-Hemolysin, by causing membrane permeability defects, could allow calcium influx, which initiates macrophage apoptosis. GBS also induces apoptosis in human monocytes but not in tumor lines demonstrating the specificity of its activity. This study suggests that induction of macrophage apoptosis by GBS is a novel strategy to overcome host immune defenses.