Michael J. Herron

Candida mannan: chemistry, suppression of cell-mediated immunity, and possible mechanisms of action.

The ability of Candida albicans to establish an infection involves multiple components of this fungal pathogen, but its ability to persist in host tissue may involve primarily the immunosuppressive property of a major cell wall glycoprotein, mannan. Mannan and oligosaccharide fragments of mannan are potent inhibitors of cell-mediated immunity and appear to reproduce the immune deficit of patients with the mucocutaneous form of candidiasis. However, neither the exact structures of these inhibitory species nor their mechanisms of action have yet been clearly defined. Different investigators have proposed that mannan or mannan catabolites act upon monocytes or suppressor T lymphocytes, but research from unrelated areas has provided still other possibilities for consideration. These include interference with cytokine activities, lymphocyte-monocyte interactions, and leukocyte homing. To stimulate further research of the immunosuppressive property of C. albicans mannan, we have reviewed (i) the relationship of mannan to other antigens and virulence factors of the fungus; (ii) the chemistry of mannan, together with methods for preparation of mannan and mannan fragments; and (iii) the historical evidence for immunosuppression by Candida mannan and the mechanisms currently proposed for this property; and (iv) we have speculated upon still other mechanisms by which mannan might influence host defense functions. It is possible that understanding the immunosuppressive effects of mannan will provide clues to novel therapies for candidiasis that will enhance the efficacy of both available and future anti-Candida agents.

ANTI-INFLAMMATORY ACTION OF DAPSONE : INHIBITION OF NEUTROPHIL ADHERENCE IS ASSOCIATED WITH INHIBITION OF CHEMOATTRACTANT-INDUCED SIGNAL TRANSDUCTION

Dapsone has clinical utility as an anti‐inflammatory agent but the mechanism of this action remains unknown. We have previously reported that dapsone inhibits β2 integrin (CD11b/CD18) ‐mediated adherence of human neutrophils in vitro and now describe studies designed to discover how dapsone‐mediated inhibition of this neutrophil function occurs. Results indicate that dapsone interferes with the activation or function of the G‐protein (Gi type) that initiates the signal transduction cascade common to chemotactic stimuli. They also show that dapsone‐mediated suppression of this pathway inhibits the generation of second messengers essential to the activation of β2 integrin molecules, as well as respiratory and secretory functions of neutrophils exposed to chemoattractants. We propose that the inhibition of chemoattractant‐induced signal transduction by dapsone suppresses neutrophil recruitment and local production of toxic respiratory and secretory products in the affected skin of dermatitis herpetiformis and other neutrophilic dermatoses. J. Leukoc. Biol. 62: 827–836; 1997.

Microbial mineral weathering for nutrient acquisition releases arsenic.

ABSTRACT Tens of millions of people in Southeast Asia drink groundwater contaminated with naturally occurring arsenic. How arsenic is released from the sediment into the water remains poorly understood. Here, we show in laboratory experiments that phosphate-limited cells of Burkholderia fungorum mobilize ancillary arsenic from apatite. We hypothesize that arsenic mobilization is a by-product of mineral weathering for nutrient acquisition. The released arsenic does not undergo a redox transformation but appears to be solubilized from the apatite mineral lattice during weathering. Analysis of apatite from the source area in the Himalayan basin indicates the presence of elevated levels of arsenic, with an average concentration of 210 mg/kg. The rate of arsenic release is independent of the initial dissolved arsenic concentration and occurs at phosphate levels observed in Bangladesh aquifers. We also demonstrate the presence of the microbial phenotype that releases arsenic from apatite in Bangladesh aquifer sediments and groundwater. These results suggest that microbial mineral weathering for nutrient acquisition could be an important mechanism for arsenic mobilization.

Whole genome transcription profiling of Anaplasma phagocytophilum in human and tick host cells by tiling array analysis

BackgroundAnaplasma phagocytophilum (Ap) is an obligate intracellular bacterium and the agent of human granulocytic anaplasmosis, an emerging tick-borne disease. Ap alternately infects ticks and mammals and a variety of cell types within each. Understanding the biology behind such versatile cellular parasitism may be derived through the use of tiling microarrays to establish high resolution, genome-wide transcription profiles of the organism as it infects cell lines representative of its life cycle (tick; ISE6) and pathogenesis (human; HL-60 and HMEC-1).ResultsDetailed, host cell specific transcriptional behavior was revealed. There was extensive differential Ap gene transcription between the tick (ISE6) and the human (HL-60 and HMEC-1) cell lines, with far fewer differentially transcribed genes between the human cell lines, and all disproportionately represented by membrane or surface proteins. There were Ap genes exclusively transcribed in each cell line, apparent human- and tick-specific operons and paralogs, and anti-sense transcripts that suggest novel expression regulation processes. Seven virB2 paralogs (of the bacterial type IV secretion system) showed human or tick cell dependent transcription. Previously unrecognized genes and coding sequences were identified, as were the expressed p44/msp2 (major surface proteins) paralogs (of 114 total), through elevated signal produced to the unique hypervariable region of each – 2/114 in HL-60, 3/114 in HMEC-1, and none in ISE6.ConclusionUsing these methods, whole genome transcription profiles can likely be generated for Ap, as well as other obligate intracellular organisms, in any host cells and for all stages of the cell infection process. Visual representation of comprehensive transcription data alongside an annotated map of the genome renders complex transcription into discernable patterns.

Transformation of Anaplasma phagocytophilum

BackgroundTick-borne pathogens cause emerging zoonoses, and include fastidious organisms such as Anaplasma phagocytophilum. Because of their obligate intracellular nature, methods for mutagenesis and transformation have not been available.ResultsTo facilitate genetic manipulation, we transformed A. phagocytophilum (Ap) to express a green fluorescent protein (GFP) with the Himar1 transposase system and selection with the clinically irrelevant antibiotic spectinomycin.ConclusionThese transformed bacteria (GFP/Ap) grow at normal rates and are brightly fluorescent in human, monkey, and tick cell culture. Molecular characterization of the GFP/Ap genomic DNA confirmed transposition and the flanking genomic insertion locations were sequenced. Three mice inoculated with GFP/Ap by intraperitoneal injection became infected as demonstrated by the appearance of morulae in a peripheral blood neutrophil and re-isolation of the bacteria in culture.

The interactions of Anaplasma phagocytophilum, endothelial cells, and human neutrophils.

Abstract: Ixodes scapularis ticks transmit Anaplasma phagocytophilum (Ap), agent of human granulocytic anaplasmosis (HGA). Invasion of neutrophil granulocytes (PMN) by Ap is the hallmark of the disease, but these short‐lived phagocytes are not likely the sole cell type required for productive infection. We analyzed infection of microvascular endothelial cells during pathogenesis of anaplasmosis in vivo and in vitro. Organs from Ap‐infected mice were processed for confocal microscopy 41 days p.i. Fluorescent labeling of heart and liver sections using anti‐factor VIII and anti‐MSP2 antibodies allowed colocalization of Ap and vascular endothelium, indicating infection. Ap rapidly invaded and grew within HMEC‐1 human microvascular endothelial cells and readily transferred to PMN. Over 50% of PMN became infected within two hours of coincubation with HMEC‐1. PMN adhered to, polarized, and migrated upon infected endothelial monolayers. The Ap receptor on human PMN is PSGL‐1, and infected endothelial cells upregulate ICAM‐1 (CD54), but the mechanisms of transfer of Ap remain unknown. To elucidate the cellular determinants involved, we tested relevant antibodies and lectins. Anti‐PSGL‐1 reduced infection of PMN, but did not inhibit adherence of PMN to Ap infected HMEC‐1 cells while anti‐CD18 did. Sialidase pretreatment increased, and EDTA and fucoidan decreased binding of Ap to HMEC‐1, whereas several other lectins had no effect. An endothelial reservoir of Ap offers opportunities for ongoing, direct cell‐to‐cell infection of PMN, avoidance of host immune effectors, and completion of the Ap life cycle by infection of circulating leukocytes available for transfer to blood‐feeding ticks.

Tumor-induced mechanical hyperalgesia involves CGRP receptors and altered innervation and vascularization of DsRed2 fluorescent hindpaw tumors.

Functional and anatomical relationships among primary afferent fibers, blood vessels, and cancers are poorly understood. However, recent evidence suggests that physical and biochemical interactions between these peripheral components are important to both tumor biology and cancer‐associated pain. To determine the role of these peripheral components in a mouse model of cancer pain, we quantified the change in nerve and blood vessel density within a fibrosarcoma tumor mass using stereological analysis of serial confocal optical sections of immunostained hind paw. To this end we introduced the Discoma coral‐derived red fluorescent protein (DsRed2) into the NCTC 2472 fibrosarcoma line using the Sleeping Beauty transposon methodology, thus providing a unique opportunity to visualize tumor–nerve–vessel associations in context with behavioral assessment of tumor‐associated hyperalgesia. Tumors from hyperalgesic mice are more densely innervated with calcitonin gene related peptide (CGRP)‐immunoreactive nerve fibers and less densely vascularized than tumors from non‐hyperalgesic mice. As hyperalgesia increased from Day 5 to 12 post‐implantation, the density of protein gene product 9.5 (PGP9.5)‐immunoreactive nerves and CD31‐immunoreactive blood vessels in tumors decreased, whereas CGRP‐immunoreactive nerve density remained unchanged. Importantly, intra‐tumor injection of a CGRP1 receptor antagonist (CGRP 8–37) partially blocked the tumor‐associated mechanical hyperalgesia, indicating that local production of CGRP may contribute to tumor‐induced nociception through a receptor‐mediated process. The results describe for the first time the interaction among sensory nerves, blood vessels and tumor cells in otherwise healthy tissue, and our assessment supports the hypothesis that direct tumor cell‐axon communication may underlie, at least in part, the occurrence of cancer pain.

Analysis of fluorescent protein expression in transformants of Rickettsia monacensis, an obligate intracellular tick symbiont

ABSTRACT We developed and applied transposon-based transformation vectors for molecular manipulation and analysis of spotted fever group rickettsiae, which are obligate intracellular bacteria that infect ticks and, in some cases, mammals. Using the Epicentre EZ::TN transposon system, we designed transposons for simultaneous expression of a reporter gene and a chloramphenicol acetyltransferase (CAT) resistance marker. Transposomes (transposon-transposase complexes) were electroporated into Rickettsia monacensis, a rickettsial symbiont isolated from the tick Ixodes ricinus. Each transposon contained an expression cassette consisting of the rickettsial ompA promoter and a green fluorescent protein (GFP) reporter gene (GFPuv) or the ompB promoter and a red fluorescent protein reporter gene (DsRed2), followed by the ompA transcription terminator and a second ompA promoter CAT gene cassette. Selection with chloramphenicol gave rise to rickettsial populations with chromosomally integrated single-copy transposons as determined by PCR, Southern blotting, and sequence analysis. Reverse transcription-PCR and Northern blots demonstrated transcription of all three genes. GFPuv transformant rickettsiae exhibited strong fluorescence in individual cells, but DsRed2 transformants did not. Western blots confirmed expression of GFPuv in R. monacensis and in Escherichia coli, but DsRed2 was expressed only in E. coli. The DsRed2 gene, but not the GFPuv gene, contains many GC-rich amino acid codons that are rare in the preferred codon suite of rickettsiae, possibly explaining the failure to express DsRed2 protein in R. monacensis. We demonstrated that our vectors provide a means to study rickettsia-host cell interactions by visualizing GFPuv-fluorescent R. monacensis associated with actin tails in tick host cells.

A Novel System for Simultaneous in Vivo Tracking and Biological Assessment of Leukemia Cells and ex Vivo Generated Leukemia-Reactive Cytotoxic T Cells

To determine the mechanisms by which adoptive immunotherapy could reduce lethality to acute myelogenous leukemia (AML), a novel technique was developed to track both leukemic blasts and adoptively transferred cytotoxic T cells (CTLs) independently and simultaneously in mice. To follow the fate of ex vivo generated anti-AML-reactive CTLs, splenocytes obtained from enhanced green fluorescent protein transgenic mice were cocultured with AML lysate-pulsed dendritic cells, which subsequently were expanded by exposure to anti-CD3/CD28 monoclonal antibody-coated magnetic microspheres. To track AML cells, stable transfectants of C1498 expressing DsRed2, a red fluorescent protein, were generated. Three factors related to CTLs correlated with disease-free survival: (a) CTL l-selectin expression. l-Selectin high fractions resulted in 70% disease-free survival, whereas l-selectin low-expressing CTLs resulted in only 30% disease-free survival. (b) Duration of ex vivo expansion (9 versus 16 days). Short-term expanded CTLs could be found at high frequency in lymphoid organs for longer than 4 weeks after transfer, whereas long-term expanded CTLs were cleared from the system after 2 weeks. Duration of expansion correlated inversely with l-selectin expression. (c) CTL dose. A higher dose (40 versus 5 × 106) resulted in superior disease-free survival. This survival advantage was achieved with short-term expanded CTLs only. The site of treatment failure was mainly the central nervous system where no CTLs could be identified at AML sites.

Transgene expression and silencing in a tick cell line: A model system for functional tick genomics.

The genome project of the black legged tick, Ixodes scapularis, provides sequence data for testing gene function and regulation in this important pathogen vector. We tested Sleeping Beauty (SB), a Tc1/mariner group transposable element, and cationic lipid-based transfection reagents for delivery and genomic integration of transgenes into I. scapularis cell line ISE6. Plasmid DNA and dsRNA were effectively transfected into ISE6 cells and they were successfully transformed to express a red fluorescent protein (DsRed2) and a selectable marker, neomycin phosphotransferase (NEO). Frequency of transformation was estimated as 1 transformant per 5000-10,000 cells and cultures were incubated for 2-3 months in medium containing the neomycin analog G418 in order to isolate transformants. Genomic integration of the DsRed2 transgene was confirmed by inverse PCR and sequencing that demonstrated a TA nucleotide pair inserted between SB inverted/direct repeat sequences and tick genomic sequences, indicating that insertion of the DsRed2 gene into the tick cell genome occurred through the activity of SB transposase. RNAi using dsRNA transcribed from the DsRed2 gene silenced expression of red fluorescent protein in transformed ISE6 cells. SB transposition in cell line ISE6 provides an effective means to explore the functional genomics of I. scapularis.