Effects of fibronectin on actin organization and respiratory burst activity in neutrophils, monocytes, and macrophages

PRELP Enhances Host Innate Immunity against the Respiratory Tract Pathogen Moraxella catarrhalis

Respiratory tract infections are one of the leading causes of mortality worldwide urging better understanding of interactions between pathogens causing these infections and the host. Here we report that an extracellular matrix component proline/arginine-rich end leucine-rich repeat protein (PRELP) is a novel antibacterial component of innate immunity. We detected the presence of PRELP in human bronchoalveolar lavage fluid and showed that PRELP can be found in alveolar fluid, resident macrophages/monocytes, myofibroblasts, and the adventitia of blood vessels in lung tissue. PRELP specifically binds respiratory tract pathogens Moraxella catarrhalis, Haemophilus influenzae, and Streptococcus pneumoniae, but not other bacterial pathogens tested. We focused our study on M. catarrhalis and found that PRELP binds the majority of clinical isolates of M. catarrhalis (n = 49) through interaction with the ubiquitous surface protein A2/A2H. M. catarrhalis usually resists complement-mediated serum killing by recruiting to its surface a complement inhibitor C4b-binding protein, which is also a ligand for PRELP. We found that PRELP competitively inhibits binding of C4b-binding protein to bacteria, which enhances membrane attack complex formation on M. catarrhalis and thus leads to increased serum sensitivity. Furthermore, PRELP enhances phagocytic killing of serum-opsonized M. catarrhalis by human neutrophils in vitro. Moreover, PRELP reduces Moraxella adherence to and invasion of human lung epithelial A549 cells. Taken together, PRELP enhances host innate immunity against M. catarrhalis through increasing complement-mediated attack, improving phagocytic killing activity of neutrophils, and preventing bacterial adherence to lung epithelial cells.

Mammary gland involution as an immunotherapeutic target for postpartum breast cancer

Postpartum mammary gland involution has been identified as tumor-promotional and is proposed to contribute to the increased rates of metastasis and poor survival observed in postpartum breast cancer patients. In rodent models, the involuting mammary gland microenvironment is sufficient to induce enhanced tumor cell growth, local invasion, and metastasis. Postpartum involution shares many attributes with wound healing, including upregulation of genes involved in immune responsiveness and infiltration of tissue by immune cells. In rodent models, treatment with non-steroidal anti-inflammatory drugs (NSAIDs) ameliorates the tumor-promotional effects of involution, consistent with the immune milieu of the involuting gland contributing to tumor promotion. Currently, immunotherapy is being investigated as a means of breast cancer treatment with the purpose of identifying ways to enhance anti-tumor immune responses. Here we review evidence for postpartum mammary gland involution being a uniquely defined 'hot-spot' of pro-tumorigenic immune cell infiltration, and propose that immunotherapy should be explored for prevention and treatment of breast cancers that arise in this environment.

Toxins-useful biochemical tools for leukocyte research

Leukocytes are a heterogeneous group of cells that display differences in anatomic localization, cell surface phenotype, and function. The different subtypes include e.g., granulocytes, monocytes, dendritic cells, T cells, B cells and NK cells. These different cell types represent the cellular component of innate and adaptive immunity. Using certain toxins such as pertussis toxin, cholera toxin or clostridium difficile toxin, the regulatory functions of Gα_i, Gαs and small GTPases of the Rho family in leukocytes have been reported. A summary of these reports is discussed in this review.

Fragments of extracellular matrix as mediators of inflammation. Int J Biochem Cell Biol. 2008;40:1101-1110. [PMID: 18243041 DOI: 10.1016/j.biocel.2007.12.005]

Classically, the extracellular matrix (ECM) was viewed as a supporting structure for stabilizing the location of cells in tissues and for preserving the architecture of tissues. This conception has changed dramatically over the past few decades with discoveries that ECM has profound influences on the structure, viability, and functions of cells. Much of the data supporting this new paradigm has been obtained from studies of normal and pathological structural cells such as fibroblasts, smooth muscle cells, and malignant cells, as, for example, breast cancer epithelial cells. However, there has also been recognition that effects of ECM on cells extend to inflammatory cells. In this context, attention has been drawn to fragments of ECM components. In this review, we present information supporting the concept that proteolytic fragments of ECM affect multiple functions and properties of inflammatory and immune cells. Our focus is particularly upon neutrophils, monocytes, and macrophages and fragments derived from collagens, elastin, and laminins. Hyaluronan fragments, although they are not products of proteolysis, are also discussed, as they are a notable example of ECM fragments that exhibit important effects on inflammatory cells. Further, we summarize some exciting recent developments in this field as a result of mouse models in which defined ECM fragments and their receptors are clearly implicated in inflammation in vivo. Thus, this review underscores the idea that proteolysis of ECM may well have implications that go beyond modifying the structural environment of cells and tissues.

IL-12-independent Th1 polarization in human mononuclear cells infected with varicella-zoster virus

T helper type 1 (Th1) cells perform a critical role in fighting intracellular organisms, and interleukin-12 (IL-12) is known to promote a Thl response. This study was conducted to identify whether an IL-12-independent Th1 reaction is induced by the varicella-zoster virus (VZV) in human beings. It was found that different intracellular microorganisms could induce IFNgamma but not IL-12 production. Induction of IFNgamma production by VZV was associated with IFNalpha production and phosphorylation of both the signal transducer and activator of transcription-1 (STAT-1) and STAT-4 in lymphocytes. In contrast, Bacillus Calmette-Guerin (BCG) induced IL-12 production in association with STAT-4 but not STAT-1 activation. Anti-IFNalpha but not anti-IL-12 antibodies blocked the VZV-induced Th1 polarization. A patient with an IL-12 receptor beta1 chain deficiency showed a normal VZV- but not a normal BCG-induced Th1 reaction, further supporting the concept of an IFNalpha-mediated, IL-12-independent Th1 reaction in response to certain intracellular infections. Identification of the early Th1 polarization induced by IFNalpha versus IL-12 in response to specific viruses may enable the development of better therapeutic strategies tailored to different infections.

Angiotensin II-induced oxidative burst is fluvastatin sensitive in neutrophils of patients with hypercholesterolemia

The aim of this study was to investigate the effect of the 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor fluvastatin (Flu) on angiotensin II (AII)-stimulated neutrophils of patients with hypercholesterolemia. Results suggest that a 6-week-long Flu administration completely counteracted the AII-induced increase in superoxide anion and leukotriene C4 production of the neutrophils of patients with hypercholesterolemia. However, the failure of signal processing through pertussis toxin-sensitive G protein, the increase in [Ca2+]i in membrane-bound protein kinase C activity, and the increase in neutrophil-bound cholesterol content were only partially restored by Flu. In addition, Flu had no effect on the increased membrane rigidity of the neutrophils of patients with hypercholesterolemia. To sum it up, Flu administration had a beneficial effect on AII-triggered reactive oxygen species generation; it resulted in partial restoration of signaling processes and of membrane composition, but membrane fluidity remained unchanged.

A model to study neurotropism and persistency of Japanese encephalitis virus infection in human neuroblastoma cells and leukocytes

Japanese encephalitis (JE) is the most common mosquito-borne encephalitis in the Asia-Pacific region. Patients with JE usually present neuronal involvement, but other organ involvement is relatively rare. Employing human neuroblast-derived (NB) cell lines and different blood cells (erythrocytes, lymphocytes, granulocytes and monocytes), the neurotropism and persistency of Japanese encephalitis virus (JEV) in human cells was investigated. It was found that JEV could not replicate in erythrocytes, granulocytes or lymphocytes. Monocytes and NB cell lines could support replication of JEV as demonstrated by expression of viral NS3 antigen and virus plaque-forming units (p.f.u.). JEV could replicate more efficiently in neuroblastoma (HTB-11) cells than in monocytes after infection for 48 h (2.1+/-1.2x10(7) vs 2.8+/-0.7x10(2) p.f.u. ml(-1)). Two different strains of JEV revealed a similar infectivity to different leukocytes and four NB cell lines. In a kinetic study, it was found that JEV-infected monocytes possessed a high viability (90 %) after infection for 5 days, while JEV-infected neuroblastoma cells suffered cell apoptosis in 2 days and decreased viability to less than 1 % in 5 days. Further studies showed that monocytes could take up JEV rapidly, displaying a log scale increase of intracellular JEV titres in 9 h after infection. Significantly, extracellular production of JEV by monocytes started in 12 h, peaked in 3 days and persisted for more than 3 weeks. These results suggest that JEV-infected monocytes may play an important role in harbouring JEV for eventual transmission to NB cells and that modulation of JEV-induced NB cell apoptosis may be useful in treating patients with JE.

Involvement of heterotrimeric G proteins in phagocytosis and recycling from the phagosomal compartment

Phagocytosis is a receptor-mediated process by which specialized cell types engulf large extracellular particles. Phagosome maturation involves a series of intracellular membrane fusion and budding events resulting in the delivery of particles to compartments enriched in lysosomal hydrolases where they are digested. Substantial amounts of plasma membrane and many phagosomal proteins, such as receptors, rapidly recycle to the plasma membrane following phagosome formation. Despite the importance of this recycling pathway in phagosome maturation and in the retrieval of immunogenic peptides from phagosomes, the molecular machinery involved is largely unknown. To assess the participation of GTPases in phagocytosis and recycling from phagosomes we used aluminum fluoride (AIF(-)(4)), which activates the GDP-bound form of stimulatory and inhibitory trimeric G proteins. AlF(-)(4) inhibited both the uptake to and the recycling from the phagosomal compartment. Cholera toxin, which activates Galphas, and pertussis toxin, which uncouples Gi and Go from receptors, were effective inhibitors of phagocytosis. However, both toxins stimulated recycling from phagosomes. These results suggest that more than one GTP-binding protein participates either directly or indirectly not only in phagocytosis, but also in maturation and recycling from phagosomes, and thereby assign a role for heterotrimeric G proteins in controlling traffic through the phagocytic pathway.

A model of the real-time correlation of viral titers with immune reactions in antibody-dependent enhancement of dengue-2 infections

We simultaneously assessed dengue-2 virus (DEN-2) titers by real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR) and immune reactions including interleukin-4 (IL-4), interferon-gamma (IFN-gamma) and prostaglandin E(2) (PGE(2)) production by human mononuclear cells (MNLs) in a model of antibody-dependent enhancement (ADE). We found that DEN-1 immune sera at 1:100 and 1:250, but not those at 1:10 or control sera, enhanced DEN-2 infections in human MNLs as assessed by the fluorogenic RT-PCR technique. The enhanced profiles of DEN-2 infections determined by the RT-PCR in 6 h were reproducible by the standard plaque-forming unit (PFU) measurement established after 7 days. The ADE-enhanced DEN-2 titers determined by the RT-PCR were 5.5-33-fold higher than those detected by PFU assay, suggesting that total virions during infections were much higher than the viable ones detected by PFU assay. MNLs in response to DEN-2 infections had higher IFN-gamma and PGE(2) production. However, the enhancement of DEN-2 infections by DEN-1 immune sera in MNLs was not associated with further enhancement of IFN-gamma production. In contrast, the presence of subneutralizing DEN-1 immune sera that enhanced DEN-2 infections also enhanced PGE(2) but not IL-4 production. The results of this study suggest that ADE of DEN-2 infections associated with induction of immunosuppressive mediators such as PGE(2) and IL-4 can be simultaneously assessed in a real-time fashion.

A model to study antioxidant regulation of endotoxemia-modulated neonatal granulopoiesis and granulocyte apoptosis

Neonates with septicemia tend to develop granulocytopenia, which may, in part, be due to septic mediators such as oxygen free radicals and tumor necrosis factor alpha (TNF-alpha). Granulocytopenia may be caused by a decrease in granulocyte growth and/or an increase in granulocyte destruction. In the present study, we investigated antioxidant regulation of endotoxin-modulated neonatal granulopoiesis and granulocyte apoptosis. Using human umbilical cord blood (HUCB), we found that simulating endotoxemia in vitro elicited significant superoxide production within a few minutes. Endotoxin exposure suppressed colony-forming unit-granulocyte and monocyte formation in a dose-dependent fashion. Addition of antioxidants such as N-acetyl-cysteine could reverse the endotoxin suppression of colony-forming unit-granulocyte and monocyte formation (13 +/- 5 versus 75 +/- 5 colony-forming units/mL). Spontaneous in vitro granulocyte apoptosis in 6 h, as reflected by phosphatidylserine expression on the cell surface, was higher in granulocytes from HUCB than in those from adult blood (10.8 +/- 1.0% versus 5.6 +/- 1.2%). The addition of endotoxin or IL-8 to the cells in the in vitro model did not promote granulocyte apoptosis, but TNF-alpha, a major mediator of the effects of endotoxin, significantly induced granulocyte apoptosis in HUCB (control versus TNF-alpha: 8.9 +/- 1.2% versus 35.9 +/- 2.9%). Addition of the antioxidant N-acetyl-cysteine effectively blocked TNF-alpha-induced granulocyte apoptosis as demonstrated by DNA fragmentation. Results from these studies indicate that oxygen radicals are directly involved in endotoxin suppression of granulopoiesis, and indirectly promote granulocyte apoptosis, presumably through TNF-alpha-mediated action. Thus, under certain conditions, modulation of oxygen radical production in the blood may benefit neonates with granulocytopenia.

Effect of glutamine on Th1 and Th2 cytokine responses of human peripheral blood mononuclear cells

Decreased glutamine concentrations are found in patients with catabolic stress and are related to susceptibility to infections. In this study, we evaluated the role of glutamine in Th1/Th2 cytokine responses. Peripheral blood mononuclear cells were stimulated with phytohemagglutinin (PHA), live attenuated bacillus Calmette-Guérin (BCG), or measles virus in the presence of different glutamine concentrations. We found that glutamine at an optimal concentration (0.6 mM) significantly enhanced PHA-stimulated lymphocyte proliferation as well as Th1 [interferon-gamma (IFN-gamma) and interleukin-2 (IL-2)] and Th2 cytokine (IL-4 and IL-10) production. In the absence of glutamine, BCG and measles virus elicited minimal lymphocyte proliferation, whereas BCG enhanced Th1 cytokine response and measles virus promoted Th2 cytokine response. Interestingly, addition of glutamine promoted the BCG-elicited Th1 cytokine response (IFN-gamma), but suppressed the measles-induced Th2 cytokine response (IL-10). These results suggest that appropriate glutamine levels may influence host responses to different antigens and microorganisms. Furthermore, predominately Th1, but not Th2, cytokine responses required the presence of optimal concentrations of glutamine.

Attenuation of ozone-induced lung injury by interleukin-10

Ozone (O3), an oxidant air pollutant, is capable of producing pulmonary inflammation and injury. Exposure to O3 results in the release of inflammatory cytokines including tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1) by alveolar macrophages. In addition, O3 exposure results in an increased expression of the inducible isoform of nitric oxide synthetase (iNOS). Interleukin-10 (IL-10) is an anti-inflammatory cytokine which inhibits the synthesis of TNF-alpha and IL-1 by macrophages and decreases the expression of iNOS. To test the protective properties of IL-10 in vivo, on the pulmonary injury induced by O3 exposure, we intratracheally instilled rat recombinant IL-10 1 h prior to O3 exposure (0.8 ppm x 3 h). Approximately 10-12 h following exposure, the animals were sacrificed and the bronchoalveolar lavage fluid (BALF) collected. The quantification of albumin, protein and fibronectin in the BALF provided a means of assessing pulmonary injury while the analysis of the BALF cells reflected the inflammatory response. Ozone exposure resulted in a significant (P<0.05) increase in BALF albumin, protein and fibronectin content as compared to air-exposed controls. In addition, significant increases in the percentage of BALF polymorphonuclear leukocytes (PMNs) and tissue expression of fibronectin mRNA were observed. The intratracheal instillation of IL-10 prior to O3 exposure resulted in a significant reduction in BALF albumin, protein and fibronectin content, and lung fibronectin mRNA as compared to O3 exposure alone. The data shows that IL-10, when given intratracheally, significantly reduces the pulmonary injury following O3 exposure in the rat. However, since the PMNs and the levels of albumin, protein and fibronectin in the IL-10 treated group did not reach baseline values, we conclude that other mediators of inflammation and injury not regulated by IL-10 also contribute to the pathophysiology of O3-induced lung injury.

Lymphocyte proliferation modulated by glutamine: involved in the endogenous redox reaction

Decreased glutamine concentrations are found during catabolic stress and are related to susceptibility to infections. However, little is known about the mechanism of glutamine modulation of lymphocyte functions. Glutamine is not only an important energy source in mitochondria, but is also a precursor of glutamate, which is used for cellular glutathione (GSH) biosynthesis in lymphocytes. In this study, we investigated the effects of glutamine on the redox reaction during lymphocyte proliferation. Peripheral blood mononuclear cells, obtained from healthy adult volunteers, were cultured and stimulated by phytohaemagglutinin (PHA) in the presence of different glutamine concentrations. Cells were harvested and prepared for analysis of lymphocyte proliferation, cell cycle propagation, intracellular glutathione levels and reactive oxygen species (ROS) production. We found that glutamine supplementation significantly enhanced PHA-stimulated lymphocyte proliferation and propagation of the cell cycle from the G1 to S and G2/M phases. Glutamine also enhanced production of both intracellular ROS and GSH levels in PHA-stimulated lymphocytes. Flow cytometric analysis by the mercury orange staining method showed that glutamine significantly enhanced intracellular non-protein thiols in PHA-stimulated CD4+, but not CD8+ lymphocyte subsets. Furthermore, intracellular GSH detected by monochlorobimane dye probe showed that glutamine enhanced GSH both in PHA-stimulated CD4+ and CD8+ lymphocyte subsets. Inadequate glutamine supplementation resulted in decreased lymphocyte proliferation in association with decreased levels of intracellular GSH. Addition of exogenous GSH significantly enhanced lymphocyte proliferation, whereas blockade of GSH synthesis enhanced ROS production and suppressed lymphocyte proliferation. These results suggest that the modulation of PHA-stimulated lymphocyte proliferation by glutamine is closely related to the maintenance of appropriate intracellular redox status.

Alteration of Actin Organization by Jaspamide Inhibits Ruffling, but not Phagocytosis or Oxidative Burst, in HL-60 Cells and Human Monocytes

Jaspamide, a naturally occurring cyclic peptide isolated from the marine sponge Hemiastrella minor, has fungicidal and growth-inhibiting activities. Exposure of promyelocytic HL-60 cells and human monocytes to jaspamide induces a dramatic reorganization of actin from a typical fibrous network to focal aggregates. HL-60 cells exposed to 5 × 10−8 mol/L or 10−7 mol/L jaspamide exhibited a reduced proliferation rate. In addition, 10−7mol/L jaspamide induced maturation of HL-60 cells as indicated by the appearance of a lobulated nucleus in 55% ± 5% of the cells and immunophenotypic maturation of the leukemia cells (upregulation of CD16 and CD14 B antigens). Further characterization has shown that F-actin is aggregated both in HL-60 cells and in human monocytes exposed to 10−7 mol/L jaspamide. Well-spread cultured human monocytes contracted and adopted round shapes after treatment with jaspamide. Moreover, a dose-dependent increase in both total actin and de novo synthesized portions of the soluble actin was observed in jaspamide-treated HL-60 cells. Jaspamide treatment inhibits ruffling and intracellular movement in HL-60 cells and monocytes, but does not affect phagocytic activity or respiratory burst activity. The consequential effects of jaspamide-induced actin reorganization on ruffling, versus its negligible effect on phagocytosis and oxidative burst, may shed light on molecular mechanisms of actin involvement in these processes. Jaspamide disrupts the actin cytoskeleton of normal and malignant mammalian cells with no significant effect on phagocytic activity and may, therefore, be considered as a novel therapeutic agent.

Alteration of Actin Organization by Jaspamide Inhibits Ruffling, but not Phagocytosis or Oxidative Burst, in HL-60 Cells and Human Monocytes

Jaspamide, a naturally occurring cyclic peptide isolated from the marine sponge Hemiastrella minor, has fungicidal and growth-inhibiting activities. Exposure of promyelocytic HL-60 cells and human monocytes to jaspamide induces a dramatic reorganization of actin from a typical fibrous network to focal aggregates. HL-60 cells exposed to 5 × 10−8 mol/L or 10−7 mol/L jaspamide exhibited a reduced proliferation rate. In addition, 10−7mol/L jaspamide induced maturation of HL-60 cells as indicated by the appearance of a lobulated nucleus in 55% ± 5% of the cells and immunophenotypic maturation of the leukemia cells (upregulation of CD16 and CD14 B antigens). Further characterization has shown that F-actin is aggregated both in HL-60 cells and in human monocytes exposed to 10−7 mol/L jaspamide. Well-spread cultured human monocytes contracted and adopted round shapes after treatment with jaspamide. Moreover, a dose-dependent increase in both total actin and de novo synthesized portions of the soluble actin was observed in jaspamide-treated HL-60 cells. Jaspamide treatment inhibits ruffling and intracellular movement in HL-60 cells and monocytes, but does not affect phagocytic activity or respiratory burst activity. The consequential effects of jaspamide-induced actin reorganization on ruffling, versus its negligible effect on phagocytosis and oxidative burst, may shed light on molecular mechanisms of actin involvement in these processes. Jaspamide disrupts the actin cytoskeleton of normal and malignant mammalian cells with no significant effect on phagocytic activity and may, therefore, be considered as a novel therapeutic agent.

Interaction Between α5β1 Integrin and Secreted Fibronectin Is Involved in Macrophage Differentiation of Human HL-60 Myeloid Leukemia Cells

We examined the role of fibronectin (FN) and FN-binding integrins in macrophage differentiation. Increased FN and α5β1 integrin gene expression was observed in phorbol 12-myristate 13-acetate PMA-treated HL-60 cells and PMA- or macrophage-CSF-treated blood monocytes before the manifestation of macrophage markers. After treatment of HL-60 cells and monocytes, newly synthesized FN was released and deposited on the dishes. An HL-60 cell variant, HL-525, which is deficient in the protein kinase Cβ (PKC-β) and resistant to PMA-induced differentiation, failed to express FN after PMA treatment. Transfecting HL-525 cells with a PKC-β expression plasmid restored PMA-induced FN gene expression and macrophage differentiation. Untreated HL-525 cells (which have a high level of the α5β1 integrin) incubated on FN differentiated into macrophages. The percentage of cells having a macrophage phenotype induced by PMA in HL-60 cells, by FN in HL-525 cells, or by either PMA or macrophage-CSF in monocytes was reduced in the presence of mAbs to FN and α5β1 integrin. The integrin-signaling nonreceptor tyrosine kinase, p72Syk, was activated in PMA-treated HL-60 and FN-treated HL-525 cells. We suggest that macrophage differentiation involves the activation of PKC-β and expression of extracellular matrix proteins such as FN and the corresponding integrins, α5β1 integrin in particular. The stimulated cells, through the integrins, attach to substrates by binding to the deposited FN. This attachment, in turn, may through integrin signaling activate nonreceptor tyrosine kinases, including p72Syk, and later lead to expression of other genes involved in evoking the macrophage phenotype.

Congenital disorders sharing oxidative stress and cancer proneness as phenotypic hallmarks: prospects for joint research in pharmacology

In spite of very distinct genotypic assets, a number of congenital conditions include oxidative stress as a phenotypic hallmark. These disorders include Fanconi's anaemia, ataxia telangiectasia, xeroderma pigmentosum and Bloom's syndrome, as well as two frequent congenital conditions: Down's syndrome and cystic fibrosis. Cancer proneness is a clinical feature shared by these disorders, while other manifestations include early ageing, neurological symptoms or congenital malformations. The onset of oxidative stress has been related to excess formation, or defective detoxification, of reactive oxygen species (ROS). This can arise from either the abnormal expression or inducibility of ROS-detoxifying enzymes, or by defective absorption of nutrient antioxidants. Resulting oxidative injury has been characterized through: (i) DNA, protein or lipid oxidative damage; (ii) excess ROS formation (in vitro and ex vivo); (iii) sensitivity to oxygen-related toxicity; (iv) improvement of cellular defects by either hypoxia or antioxidants; and (v) circumstantial evidence for in vivo oxidative stress (as e.g. clastogenic factors). Investigations conducted so far have been confined to individual disorders. Comparative studies of selected indicators for oxidative stress could provide further insights into the pathogenesis of each individual condition. Such a unified approach may have wide-ranging consequences for studies of ageing and cancer.

The effects of copper on actin and fibronectin organization in Mytilus galloprovincialis haemocytes

The effects of copper on actin and fibronectin organization in Mytilus galloprovincialis haemocytes were studied. The Cu2+ exposure of mussels caused severe perturbations in haemocyte actin and fibronectin organization with respect to non-exposed organisms. Cytoskeletal actin was analysed by indirect immunofluorescence, using an antitotal actin monoclonal antibody, and by rhodamine-conjugated phalloidin. The majority of haemocytes from Cu(2+)-exposed mussels displayed a round morphology, with short and blunt filopodia; they lacked the polarized phenotype which was typical in control samples. The cytoskeleton alteration, more evident after phalloidin staining, resulted in the disappearance of filamentous actin. The actin cortical meshwork also appeared disorganized. The cytoskeletal morphology studied by transmission electron microscopy after negative staining of Triton X-100-treated haemocytes confirmed these observations. The structural organization of actin when analysed by Western blotting showed a larger number of Triton-soluble actin pools in treated mussel haemocytes. Fibronectin was studied by indirect immunofluorescence using a polyclonal antiserum directed against mussel fibronectin. In treated mussels, fibronectin appeared to be strongly disorganized and its levels decreased in both haemocytes and haemolymph. The mechanism(s) of the copper-induced alterations on actin and fibronectin organization in mussel immunocytes is discussed.

Entry and intracellular survival of group B streptococci in J774 macrophages

The mouse macrophage-like cell line J774 was used to analyze opsonin-independent entry and survival of group B streptococci (GBS). Efficient entry of GBS in J774 cells occurred within 5 min postinfection, and streptococci persisted intracellularly without loss of viability for at least 8 h. At 24 h postinfection, 30% of the total intracellular GBS was recovered from macrophages. Inhibition studies using different biochemical modulators of cellular functions showed that bacterial entry seemed to involve nonglycosylated J774 surface structures different from known receptors such as fibronectin-binding integrins. Internalization of GBS by J774 cells occurred by a microfilament-dependent phagocytosis-like process also involving participation of receptor-mediated endocytosis. Prior opsonization of GBS with human serum containing anti-GBS antibodies did not affect bacterial entry but significantly reduced the intracellular survival of GBS. Transmission electron microscopic analysis confirmed these findings and demonstrated that both opsonized and nonopsonized bacteria were contained within phagosomes during the whole infection period. Transmission electron microscopy further revealed that decreased intracellular survival rates of opsonized GBS appeared to be due to increased lysosomal activities of the macrophages. These results suggest that in the absence of opsonins, GBS are able to enter and persist efficiently in macrophages by evading intracellular antibacterial activities commonly associated with opsonin-mediated uptake.

Characterization and immunocytochemical localization of actin and fibronectin in haemocytes of the mussel Mytilus galloprovincialis

Cell-extracellular matrix interactions are recognized to be important for human leucocyte functions, including chemotaxis and phagocytosis. These activities depend on a reorganization of the microfilament actin (F-actin) promoted by fibronectin, one of the major components of extracellular matrices. Although invertebrate haemocytes are, in many aspects, similar to the human granulocyte-monocyte-macrophage cell lineage, actin and fibronectin have not been well studied in these cells. Consequently, the characterization and structural organization of actin and fibronectin in mussel (Mytilus galloprovincialis) haemocytes was investigated using Western blotting analysis, indirect immunofluorescence and immunoelectron microscopy. Actin was immunocharacterized by an anti-total actin monoclonal antibody. Fibronectin was immunocharacterized by an autologous polyclonal antiserum directed against the protein of mussel haemolymph. Actin was mainly localized along the peripheral cytoplasm of the haemocyte. The distribution of the F-actin microfilaments was assayed with Rhodamine-labelled phalloidin. F-actin was associated mainly with stress-fibres of spreading haemocytes and with microspikes at the adhesion sites. The labelling by the anti-fibronectin antiserum of the haemocyte rough endoplasmic reticulum vesicles, revealed by immunoelectron microscopy, suggests that these cells are involved in fibronectin biosynthesis. Gold particles were also present along the outer surfaces of the cell plasma membrane and its protrusions. Mussel fibronectin was localized immunohistochemically at the adhesion sites and in the extracellular matrix fibrils. The relationships between fibronectin and the actin cytoskeleton in Mytilus galloprovincialis haemocytes are discussed.