Enhanced oxidative mechanisms in immunologically activated versus elicited polymorphonuclear neutrophils: correlations with fungicidal activity

Enhanced Spontaneous Antibacterial Activity of δ-MnO2 by Alkali Metals Doping

Recently, the widespread use of antibiotics is becoming a serious worldwide public health challenge, which causes antimicrobial resistance and the occurrence of superbugs. In this context, MnO₂ has been proposed as an alternative approach to achieve target antibacterial properties on Streptococcus mutans (S. mutans). This requires a further understanding on how to control and optimize antibacterial properties in these systems. We address this challenge by synthesizing δ-MnO₂ nanoflowers doped by magnesium (Mg), sodium (Na), and potassium (K) ions, thus displaying different bandgaps, to evaluate the effect of doping on the bacterial viability of S. mutans. All these samples demonstrated antibacterial activity from the spontaneous generation of reactive oxygen species (ROS) without external illumination, where doped MnO₂ can provide free electrons to induce the production of ROS, resulting in the antibacterial activity. Furthermore, it was observed that δ-MnO₂ with narrower bandgap displayed a superior ability to inhibit bacteria. The enhancement is mainly attributed to the higher doping levels, which provided more free electrons to generate ROS for antibacterial effects. Moreover, we found that δ-MnO₂ was attractive for in vivo applications, because it could nearly be degraded into Mn ions completely following the gradual addition of vitamin C. We believe that our results may provide meaningful insights for the design of inorganic antibacterial nanomaterials.

Effect of interleukin-10 on the Paracoccidioides brasiliensis killing by gamma-interferon activated human neutrophils

Paracoccidioidomycosis, a deep mycosis endemic in Latin America, is a chronic granulomatous disease caused by the fungus Paracoccidioides brasiliensis. Phagocytic cells play a critical role against this fungus, and several studies have shown the effects of activator and suppressive cytokines on macrophage and monocyte functions. However, studies on polymorphonuclear neutrophils (PMNs), that are the first cells recruited to the infection sites, are scarcer. Thus, the objective of this paper was to assess whether interleukin-10 (IL-10), a potent anti-inflammatory cytokine, is able to block the activity of IFN-gamma-activated human PMNs upon P. brasiliensis intracellular killing, in vitro. The results showed that IFN-gamma-activated PMNs have an effective fungicidal activity against the fungus. This activity was associated with the release of high levels of H(2)O(2), the metabolite involved in phagocytic cells antifungal activities. However, the concomitant incubation of these cells with IFN-gamma and IL-10 significantly blocked IFN-gamma activation. As a consequence, PMNs killing activity and H(2)O(2) release were inhibited. Together, our results show the importance of PMNs exposure to activator or suppressor cytokines in the early stages of paracoccidioidomycosis infection.

Defining Virulence Genes in the Dimorphic Fungi

Most dimorphic fungal pathogens cause respiratory disease in mammals and must therefore possess virulence mechanisms to combat and overcome host pulmonary defenses. Over the past decade, advances in genetic tools have made it possible to investigate the basis of dimorphic fungal pathogenesis at the molecular level. Gene disruptions and RNA interference have now formally demonstrated the involvement of six virulence factors: CBP, alpha-(1,3)-glucan, BAD1, SOWgp, Mep1, and urease. Additional candidate virulence-associated genes have been identified on the premise that factors necessary for pathogenicity are associated specifically with the parasitic form. This principle continues to form the foundation for genomics-based analyses to further augment the list. Thus, the stage is set and the tools are in place for the next phase of medical mycology research: defining the virulence-associated factors underlying the success of dimorphic fungal pathogens.

Production of pro-inflammatory cytokines during the early stages of experimentalParacoccidioides brasiliensisinfection

Pro-inflammatory cytokines play an important role in both recruitment and activation of leukocytes migrating into tissues in response to invading pathogens. In this study the production of pro-inflammatory cytokines, determined by ELISA assays, and the recruitment of leukocytes into the lungs of BALB/c mice infected with Paracoccidioides brasiliensis conidia were evaluated during the early stages of infection. The results showed that infected mice had a significant increase in leukocytes in the lung during the first 4 days with a peak at day 2 post-challenge; infiltrates were composed mainly of polymorphonuclear neutrophils (PMN). Pro-inflammatory cytokines such as tumour necrosis factor alpha (TNF-alpha), interleukin (IL) 6, IL-1beta and macrophage inflammatory protein (MIP) 2 were produced at elevated levels during the first 4 days post-challenge, but only in pulmonary samples and not in sera. Additionally, during the early stages of infection, overall weight loss was recorded in infected mice. These results suggest that pro-inflammatory cytokines could be responsible for the recruitment of leukocytes into the lung during the early stages of P. brasiliensis infection. In addition, both pro-inflammatory cytokine production and leukocyte recruitment may participate in the control of infection by influencing the organization of the immune response in the host exposed to P. brasiliensis conidia.

Antioxidant systems in the pathogenic fungi of man and their role in virulence

In the last two decades, a variety of fungal antioxidants have attracted considerable interest, largely arising from their hypothetical role as virulence determinants. Melanin is a potent free radical scavenger and in Cryptococcus neoformans, there is now good evidence that the production of melanin is a significant virulence determinant. There is also recent evidence linking melanin biosynthesis to the virulence of Aspergillus fumigatus conidia. Superoxide dismutases are important housekeeping antioxidants and have an additional hypothetical role in virulence; however, although these enzymes have been biochemically characterized from Aspergillus and Cryptococcus, there is as yet no firm evidence that these enzymes are involved in pathogenicity. Catalase production may play some role in the virulence of Candida albicans but this enzyme has not been shown, as yet, to influence the virulence of A. fumigatus. There are some data supporting an antioxidant function for the acyclic hexitol mannitol in C. neoformans, but further investigations are required in this area. Research into the putative antioxidant activities of a range of other fungal enzymes, such as acid phosphatases, remains limited at this time.

The HtrA stress response protease contributes to resistance of Brucella abortus to killing by murine phagocytes

Compared with virulent Brucella abortus 2308, the isogenic htrA mutant PHE1 shows decreased resistance to killing by cultured murine neutrophils and macrophages and significant attenuation during the early stages of infection in the BALB/c mouse model. These findings further define the contributions of the htrA gene product to the pathogenesis of B. abortus infections.

Lipopolysaccharide restores anti-Candida albicans growth inhibition activity of polymorphonuclear neutrophils from retrovirus-immunosuppressed mice

It has been documented that the immune function of leukocytes may be markedly suppressed after infection of mice with the murine retrovirus Friend leukemia virus (FLV). Antimicrobial activity of polymorphonuclear neutrophils (PMNs) against Candida albicans is impaired after retrovirus infection of mice, and this occurs as early as 3 days after infection of genetically susceptible BALB/c mice. By 2 weeks after infection, there was essentially very little growth inhibition of C. albicans by PMNs from the FLV-infected mice. However, when bacterial lipopolysaccharide (LPS), a known activator of macrophages and PMNs, was added to PMNs from the FLV-infected mice, anti-C. albicans activity was restored to normal levels. This restoration of anti-C. albicans activity of FLV-infected mouse PMNs was observed after stimulation with as little as 0.01 micrograms of LPS per ml. The data obtained show that the impaired antimicrobial function of PMNs from retrovirus-infected mice can be readily restored by a biological response modifier such as bacterial LPS.

Mechanisms of fungal pathogenicity: correlation of virulence in vivo, susceptibility to killing by polymorphonuclear neutrophils in vitro, and neutrophil superoxide anion induction among Blastomyces dermatitidis isolates

Seven Blastomyces dermatitidis isolates varying in virulence for mice were compared for susceptibility to polymorphonuclear neutrophil (PMN) killing and the ability to induce superoxide anion (O2-) production by PMNs in vitro. In vitro killing of six B. dermatitidis isolates by murine peripheral blood PMNs or by PMNs elicited from the peritoneal cavity by a local immune reaction (B. dermatitidis-immune mice given killed B. dermatitidis intraperitoneally 24 h earlier) inversely correlated with in vivo virulence (most to least virulent) isolates: VV, V, V40, KL-1, A2, and GA-1). The capacity of isolates to induce O2- production by PMNs also inversely correlated with in vivo virulence. Isolate A, of intermediate in vivo virulence, was a good inducer of O2- production in vitro but was no more susceptible to in vitro killing by PMNs than isolate V, VV, or V40. Fungal intracellular superoxide dismutase or catalase content did not correlate with in vivo virulence or in vitro killing by PMNs. Isolate A, however, had two to four times the intracellular catalase activity as did other B. dermatitidis isolates, suggesting a possible mechanism for its enhanced resistance to in vitro killing by PMNs. Therefore, while in vitro killing by PMNs and the capacity to induce O2- production by PMNs inversely correlated with virulence for six B. dermatitidis isolates, isolate A was an exception: its resistance to killing by PMN-generated oxygen metabolites in vitro but its susceptibility to killing in vivo suggest that its in vivo killing occurs by other, perhaps nonoxidative, mechanisms.

Experimental basis for the clinical epidemiology of fungal infections. A review

Based on the concept that the agents of deep fungal infections can be divided into primary pathogens and opportunists the experimental basis for the clinical epidemiology of mycoses is outlined. Kinetics of experimental infections with opportunists and primary pathogens discriminate between the two fungal categories. Natural resistance eliminates opportunists and prevents the establishment of progressive infection in the normal host. Primary pathogens call upon mechanisms of adoptive cell mediated immunity for their control. Therefore athymic mice which are not more susceptible to opportunists than control mice, cannot control infection with primary pathogens. In order to induce comparable overwhelming opportunistic mycoses with reasonable challenge doses, non-specific phagocytic resistance has to be eliminated. In agreement with in vivo studies, in vitro studies of the susceptibility of fungi to killing by phagocytes point out, that the susceptibility of the tissue phase of fungi to killing by "immunologically unarmed" phagocytes discriminates between opportunists and primary pathogens. In order to restrain primary pathogenic fungi, phagocytes have also in vitro to call upon adoptive, T cell-dependent immune mechanisms, which appear superfluous for control of opportunists. This difference explains the discrepant opportunistic proclivities of the two fungal categories. Patients with defective phagocytic defenses are prone to opportunistic mycoses, while deficient cell mediated immunity results in a greater vulnerability to primary pathogens.

In vivo activation of peripheral blood polymorphonuclear neutrophils by gamma interferon results in enhanced fungal killing

The effect of in vivo administration of murine recombinant gamma interferon (IFN) on the fungicidal activity of murine peripheral blood polymorphonuclear neutrophils (PB-PMNs) was studied. Mice were injected intramuscularly with 250, 2,500, 25,000 or 250,000 U of IFN 5 h before collection of peripheral blood. Purified PB-PMNs were cocultured in vitro with Blastomyces dermatitidis yeast cells for 2 h. PB-PMNs from untreated mice killed 44.5 +/- 12.5% of the fungal inoculum, whereas PB-PMNs from mice treated with 25,000 or 250,000 U of IFN showed significantly enhanced in vitro killing (68.0 +/- 9.4% [P less than 0.005] and 72.3 +/- 1.1% [P less than 0.001], respectively). Treatment with 250 or 2,500 U of IFN or 25,000 U of heated (100 degrees C, 15 min) IFN had no effect. The IFN-induced activation of PB-PMNs was transitory. Significant enhancement of PB-PMN killing activity occurred 1, 2, or 5 h after in vivo IFN administration, but no enhancement was observed 16 or 24 h after IFN treatment. Enhanced fungicidal activity by PB-PMNs from mice treated for 5 h with 25,000 U of IFN correlated with an increased release of superoxide anion (O2-) in vitro after stimulation of PB-PMNs with phorbol ester; normal PB-PMNs and IFN-activated PB-PMNs, respectively, produced 2.2 +/- 2.5 and 23.5 +/- 4.8 nmol of O2- per 10(6) PB-PMNs per 30 min (P less than 0.005). The exogenous addition of compounds that antagonize or inhibit the formation of oxygen radicals (superoxide dismutase, catalase, dimethyl sulfoxide, or sodium azide) significantly inhibited fungal killing by both normal and IFN-activated PB-PMNs. In addition to the enhanced microbicidal activity and superoxide generation demonstrated in vitro with constant cell numbers, there was a transient leukocytosis (particularly neutrophilia) in peripheral blood at doses of IFN and at times after IFN administration where enhanced activity was also demonstrated. In summary, our results indicate that PB-PMNs can be activated in vivo for enhanced killing of a fungal target. The enhanced killing capacity of IFN-activated PB-PMNs is due at least in part to the enhancement of oxidative killing mechanisms.

Enhanced killing of Blastomyces dermatitidis by gamma interferon-activated murine peripheral blood polymorphonuclear neutrophils

Normal peripheral blood polymorphonuclear neutrophils (PB-PMNs), challenged in vitro with yeast form Blastomyces dermatitidis, reduced inoculum colony-forming units of a virulent strain by 37.5 +/- 9.5%. Pre-incubation of PB-PMNs with 10-100,000 U/ml of purified recombinant murine gamma-interferon (IFN) for 1 h prior to challenge with fungi resulted in significant enhancement of PB-PMN fungicidal activity. No direct fungicidal activity by IFN alone was observed. Pretreatment of selected concentrations of IFN shown to have PMN-enhancing activity (100 or 1000 U/ml) with rabbit hyperimmune anti-IFN antiserum for 1 h before addition to PB-PMNs abrogated the enhancement of fungicidal activity. Isolated peripheral blood mononuclear cells failed to kill B. dermatitidis, even when mononuclear cells were present at a concentration ten times greater than that normally used in killing assays, and failed to be activated by IFN. Treatment of unstimulated or IFN-activated PB-PMNs with complement and hybridoma-derived monoclonal antibody specific for PMNs eliminated PB-PMN fungicidal activity. Exogenously added lipopolysaccharide (0.0005-50,000 ng/ml) did not activate PB-PMNs, whether added alone or in conjunction with IFN. The PB-PMN activating capacity of IFN could be destroyed by heat treatment (100 degrees C, 15 min) or by acid treatment with HCl (pH 2). These results demonstrate that recombinant gamma-interferon can stimulate PB-PMNs to kill B. dermatitidis, that the PB-PMN activating moiety is IFN and that PB-PMNs are responsible for fungal killing in this assay system.(ABSTRACT TRUNCATED AT 250 WORDS)