Experimental approaches to referential domains and the on-line processing of referring expressions in unscripted conversation

Peer reviewedPublisher PD

A systematic review of health system barriers and enablers for antiretroviral therapy (ART) for HIV-infected pregnant and postpartum women

BACKGROUND: Despite global progress in the fight to reduce maternal mortality, HIV-related maternal deaths remain persistently high, particularly in much of Africa. Lifelong antiretroviral therapy (ART) appears to be the most effective way to prevent these deaths, but the rates of three key outcomes--ART initiation, retention in care, and long-term ART adherence--remain low. This systematic review synthesized evidence on health systems factors affecting these outcomes in pregnant and postpartum women living with HIV. METHODS: Searches were conducted for studies addressing the population of interest (HIV-infected pregnant and postpartum women), the intervention of interest (ART), and the outcomes of interest (initiation, adherence, and retention). Quantitative and qualitative studies published in English since January 2008 were included. A four-stage narrative synthesis design was used to analyze findings. Review findings from 42 included studies were categorized according to five themes: 1) models of care, 2) service delivery, 3) resource constraints and governance challenges, 4) patient-health system engagement, and 5) maternal ART interventions. RESULTS: Low prioritization of maternal ART and persistent dropout along the maternal ART cascade were key findings. Service delivery barriers included poor communication and coordination among health system actors, poor clinical practices, and gaps in provider training. The few studies that assessed maternal ART interventions demonstrated the importance of multi-pronged, multi-leveled interventions. CONCLUSIONS: There has been a lack of emphasis on the experiences, needs and vulnerabilities particular to HIV-infected pregnant and postpartum women. Supporting these women to successfully traverse the maternal ART cascade requires carefully designed and targeted interventions throughout the steps. Careful design of integrated service delivery models is of critical importance in this effort. Key knowledge gaps and research priorities were also identified, including definitions and indicators of adherence rates, and the importance of cumulative measures of dropout along the maternal ART cascade

A Systematic Review of Individual and Contextual Factors Affecting ART Initiation, Adherence, and Retention for HIV-Infected Pregnant and Postpartum Women

BACKGROUND: Despite progress reducing maternal mortality, HIV-related maternal deaths remain high, accounting, for example, for up to 24 percent of all pregnancy-related deaths in sub-Saharan Africa. Antiretroviral therapy (ART) is effective in improving outcomes among HIV-infected pregnant and postpartum women, yet rates of initiation, adherence, and retention remain low. This systematic literature review synthesized evidence about individual and contextual factors affecting ART use among HIV-infected pregnant and postpartum women. METHODS: Searches were conducted for studies addressing the population (HIV-infected pregnant and postpartum women), intervention (ART), and outcomes of interest (initiation, adherence, and retention). Quantitative and qualitative studies published in English since January 2008 were included. Individual and contextual enablers and barriers to ART use were extracted and organized thematically within a framework of individual, interpersonal, community, and structural categories. RESULTS: Thirty-four studies were included in the review. Individual-level factors included both those within and outside a woman’s awareness and control (e.g., commitment to child’s health or age). Individual-level barriers included poor understanding of HIV, ART, and prevention of mother-to-child transmission, and difficulty managing practical demands of ART. At an interpersonal level, disclosure to a spouse and spousal involvement in treatment were associated with improved initiation, adherence, and retention. Fear of negative consequences was a barrier to disclosure. At a community level, stigma was a major barrier. Key structural barriers and enablers were related to health system use and engagement, including access to services and health worker attitudes. CONCLUSIONS: To be successful, programs seeking to expand access to and continued use of ART by integrating maternal health and HIV services must identify and address the relevant barriers and enablers in their own context that are described in this review. Further research on this population, including those who drop out of or never access health services, is needed to inform effective implementation

Candida albicans Septin Mutants Are Defective for Invasive Growth and Virulence

Hyphal growth of Candida albicans is implicated as an important virulence factor for this opportunistic human pathogen. Septin proteins, a family of cytoskeletal elements that regulate membrane events and are important for proper morphogenesis of C. albicans, were examined for their role in tissue invasion and virulence in the mouse model of systemic infection. In vitro, septin mutants are only mildly defective for hyphal growth in liquid culture but display pronounced defects for invasive growth into agar. In vivo, the septin mutants were found to exhibit attenuated virulence. However, mice infected with the mutants displayed high fungal burdens in their kidneys without obvious symptoms of disease. Histological examination of infected kidneys revealed defects in organ invasion for the cdc10Δ and cdc11Δ deletion mutants, which displayed both reduced tissue penetration and noninvasive fungal masses. Thus, the septin proteins are necessary for invasive growth, which appears to be more important to the successful pathogenesis of C. albicans than hyphal growth alone

<i>N</i>-acetylglucosamine (GlcNAc) Triggers a Rapid, Temperature-Responsive Morphogenetic Program in Thermally Dimorphic Fungi

<div><p>The monosaccharide <i>N</i>-acetylglucosamine (GlcNAc) is a major component of microbial cell walls and is ubiquitous in the environment. GlcNAc stimulates developmental pathways in the fungal pathogen <i>Candida albicans</i>, which is a commensal organism that colonizes the mammalian gut and causes disease in the setting of host immunodeficiency. Here we investigate GlcNAc signaling in thermally dimorphic human fungal pathogens, a group of fungi that are highly evolutionarily diverged from <i>C. albicans</i> and cause disease even in healthy individuals. These soil organisms grow as polarized, multicellular hyphal filaments that transition into a unicellular, pathogenic yeast form when inhaled by a human host. Temperature is the primary environmental cue that promotes reversible cellular differentiation into either yeast or filaments; however, a shift to a lower temperature <i>in vitro</i> induces filamentous growth in an inefficient and asynchronous manner. We found GlcNAc to be a potent and specific inducer of the yeast-to-filament transition in two thermally dimorphic fungi, <i>Histoplasma capsulatum</i> and <i>Blastomyces dermatitidis</i>. In addition to increasing the rate of filamentous growth, micromolar concentrations of GlcNAc induced a robust morphological transition of <i>H. capsulatum</i> after temperature shift that was independent of GlcNAc catabolism, indicating that fungal cells sense GlcNAc to promote filamentation. Whole-genome expression profiling to identify candidate genes involved in establishing the filamentous growth program uncovered two genes encoding GlcNAc transporters, <i>NGT1</i> and <i>NGT2</i>, that were necessary for <i>H. capsulatum</i> cells to robustly filament in response to GlcNAc. Unexpectedly, <i>NGT1</i> and <i>NGT2</i> were important for efficient <i>H. capsulatum</i> yeast-to-filament conversion in standard glucose medium, suggesting that Ngt1 and Ngt2 monitor endogenous levels of GlcNAc to control multicellular filamentous growth in response to temperature. Overall, our work indicates that GlcNAc functions as a highly conserved cue of morphogenesis in fungi, which further enhances the significance of this ubiquitous sugar in cellular signaling in eukaryotes.</p></div

Micromolar concentrations of GlcNAc are sufficient to promote morphogenesis at RT.

<p>Ten-fold serial dilutions of <i>H. capsulatum</i> yeast cells grown at 37°C were plated onto HMM solid medium supplemented with increasing concentrations of GlcNAc (HMM supplemented with 100 µM–1 mM GlcNAc) or HMM/100 mM GlcNAc medium and transferred to RT to monitor growth in the filamentous form (A) or kept at 37°C to monitor growth in the yeast form (B). Ten-fold serial dilutions of <i>H. capsulatum</i> yeast cells grown at 37°C were also plated onto HMM solid medium supplemented with either 1 mM fructose, 1 mM glucosamine (GlcN), or 1 mM GlcNAc and transferred to RT for growth in the filamentous form (C) or kept at 37°C to monitor growth in the yeast form (D). Increased growth of filamentous cells on HMM GlcNAc solid medium at RT is evident by larger colony diameter, fuzzy colony morphology, and increased visible growth at lower dilutions. Representative images are shown.</p

<i>H. capsulatum</i> Ngt1 and Ngt2 facilitate GlcNAc transport.

<p>(A) Expression of <i>H. capsulatum NGT1</i> or <i>NGT2</i> restores growth of the <i>C. albicans ngt1</i>Δ in GlcNAc media. <i>H. capsulatum NGT1</i> (Hc<i>NGT1</i>), <i>H. capsulatum NGT2</i> (Hc<i>NGT2</i>), <i>C. albicans NGT1</i> (Ca<i>NGT1</i>), or empty vector (EV) were introduced into <i>C. albicans ngt1</i>Δ yeast cells (<i>ngt1</i>Δ). Transformants were examined for growth on solid medium containing 50 mM glucose, galactose, or GlcNAc as the sole carbon source by plating serial dilutions of each strain and comparing growth to wild-type <i>C. albicans</i> (WT). Representative images are shown. (B, C, D) <i>H. capsulatum NGT1</i> and <i>NGT2</i> are necessary for growth of <i>H. capsulatum</i> in medium where GlcNAc is the only carbohydrate source. Vector control, <i>NGT1</i> RNAi, and <i>NGT2</i> RNAi strains were starved overnight to deplete available carbohydrate sources and then inoculated into 3M minimal medium containing (B) glucose, (C) GlcNAc, or (D) no carbohydrate. At each indicated timepoint, growth was evaluated by measuring the optical density at 600 nm. The standard deviation of mean OD₆₀₀ values from three independent RNAi and vector control clones for each knockdown construct are shown.</p

GlcNAc promotes morphogenesis of thermally dimorphic fungi at RT.

<p><i>H. capsulatum</i> (A, C) or <i>B. dermatitidis</i> (B, D) yeast cells grown at 37°C were inoculated into liquid HMM (“Glucose”) or HMM/100 mM GlcNAc (“GlcNAc”) medium and grown at 37°C to monitor yeast phase growth or transferred to RT to monitor conversion to filaments. Cell morphology was assessed at each indicated timepoint by confocal DIC microscopy on live cells. Scale bar, 10 µm.</p

<i>NGT1</i> and <i>NGT2</i> are required for maximal induction of GlcNAc utilization genes.

<p><i>NGT1</i> and <i>NGT2</i> transcript levels were depleted by RNAi in <i>H. capsulatum</i> and qRT-PCR was used to determine levels of (A) <i>NGT1</i> (B) <i>NGT2</i> (C) <i>DAC1</i> and (D) <i>NAG1</i> transcripts in each RNAi knockdown strain as compared to vector control cells in the absence (HMM glucose) or presence of GlcNAc (HMM/100 mM GlcNAc). Transcript levels were normalized to <i>ACT1</i>. The standard deviation of mean expression values from three independent RNAi and vector control clones is shown; p-values ≤0.02 for the comparisons of vector control versus <i>NGT</i> RNAi during GlcNAc induction of <i>NGT1</i>, <i>DAC1</i>, and <i>NAG1</i> transcripts.</p