Host immune defense against Aspergillus fumigatus: insight from experimental systemic (disseminated) infection

RNA-Seq Profile Reveals Th-1 and Th-17-Type of Immune Responses in Mice Infected Systemically with Aspergillus fumigatus

With the increasing numbers of immunocompromised hosts, Aspergillus fumigatus emerges as a lethal opportunistic fungal pathogen. Understanding innate and acquired immunity responses of the host is important for a better therapeutic strategy to deal with aspergillosis patients. To determine the transcriptome in the kidneys in aspergillosis, we employed RNA-Seq to obtain single 76-base reads of whole-genome transcripts of murine kidneys on a temporal basis (days 0; uninfected, 1, 2, 3 and 8) during invasive aspergillosis. A total of 6284 transcripts were downregulated, and 5602 were upregulated compared to baseline expression. Gene ontology enrichment analysis identified genes involved in innate and adaptive immune response, as well as iron binding and homeostasis, among others. Our results showed activation of pathogen recognition receptors, e.g., β-defensins, C-type lectins (e.g., dectin-1), Toll-like receptors (TLR-2, TLR-3, TLR-8, TLR-9 and TLR-13), as well as Ptx-3 and C-reactive protein among the soluble receptors. Upregulated transcripts encoding various differentiating cytokines and effector proinflammatory cytokines, as well as those encoding for chemokines and chemokine receptors, revealed Th-1 and Th-17-type immune responses. These studies form a basic dataset for experimental prioritization, including other target organs, to determine the global response of the host against Aspergillus infection.

A new time-dependent approach for assessment of the impact of invasive aspergillosis shows effect on short- but not on long-term survival of patients with AML or high-risk MDS

Invasive aspergillosis (IA) has been reported to yield high mortality rates. Patients with an unfavourable prognostic haematological disease not only have a higher probability of developing IA but are also more likely to die due to causes directly related to the underlying disease. This complexity of risk mechanisms confounds the causal interpretation of IA occurrence and mortality. Full consideration of the changing patient characteristics over time is necessary to obtain reliable estimates of the correlation of IA with mortality. We studied the effect of IA on mortality in 167 consecutive patients starting with remission-induction therapy for AML or of whom most patients continued to haematopoietic stem cell transplantation (HSCT). No standard antifungal prophylaxis was administered in the period before HSCT. Survival analyses were performed to determine risk estimates of IA for different phases of treatment before and after HSCT. Time-dependent adjustment for confounding variables was performed using Cox proportional hazards models. In 55 of 167 enroled patients, IA was diagnosed. Before HSCT, adjusted hazard ratios and 95% confidence intervals on mortality after the diagnosis of IA were 3.5 (1.7-7.5), 2.0 (0.69-5.9), 2.3 (0.79-6.8) and 0.80 (0.49-1.4) within 30 days, between 30 and 60 days, between 60 and 90 days or more than 90 days, respectively. A similar pattern was observed after HSCT. The occurrence of IA did not significantly influence the decision to follow through with HSCT. The results provide new insights in short- and long-term survival of patients diagnosed with IA. A significantly increased mortality risk was only observed in the first month after diagnosis of IA. No unfavourable association with mortality was observed in the later course of treatment. The occurrence of IA did not affect the probability of attaining HSCT in our population.

Immunohistochemical Analysis of Leucocyte Subsets in the Sinonasal Mucosa of Cats with Upper Respiratory Tract Aspergillosis

Leucocyte populations in the sinonasal mucosa of cats with and without upper respiratory tract aspergillosis were compared using immunohistochemistry and computer-aided morphometry. Inflammation was identified in the nasal mucosa of all affected cats, comprising predominantly of lymphoplasmacytic infiltration of the lamina propria associated with epithelial proliferation and degeneration. There was intense and diffuse expression of class II antigens of the major histocompatibility complex, associated with sites of hyphal invasion with hyperplasia and ulceration of the epithelium adjacent to fungal elements. Significantly more CD79b(+) cells, total lymphocytes, immunoglobulin (Ig)-expressing cells and MAC387(+) cells infiltrated the epithelium and more IgG(+) cells and total Ig-expressing cells infiltrated the lamina propria in affected cats compared with controls. Importantly, the inflammatory profile in affected cats was not consistent with the T helper (Th)1 and Th17 cell-mediated response that confers protective acquired immunity against invasive aspergillosis in dogs and people and in murine models of the infection. This finding may help to explain the development of invasive aspergillosis in systemically immunocompetent cats.

Relapsed and secondary disease drive the risk profile for invasive aspergillosis prior to stem cell transplantation in patients with acute myeloid leukemia or myelodysplastic syndrome

Patients with acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS) are at risk for invasive aspergillosis (IA) even prior to the introduction of stem cell transplantation (SCT). In times of increasing triazole resistance and changing use of antifungal prophylaxis, insight into the risk factors for IA is needed to improve strategies for preventing IA in this population. Consecutive patients who received remission-induction therapy for AML or MDS at the Leiden Academic Medical Centre were included. Instead of standard antifungal prophylaxis, an assertive protocol for diagnosis of suspected fungal infection was in place. IA was classified according to the revised European Organization for Research and Treatment of Cancer criteria. Potential predisposing characteristics for IA were compared by uni- and multivariate analyses. In 45 (25%) of 184 included episodes (167 patients), IA was diagnosed prior to SCT. A multivariate Cox regression model demonstrated that relapsed AML (hazard ratio [HR] 2.4; 95% confidence interval [CI], 1.1-5.1; P = 0.02), secondary AML (HR, 5.2; 95% CI, 2.3-11.8; P < 0.001), and prolonged duration of neutropenia (HR, 2.2; 95% CI, 1.2-4.0; P = 0.01) were independently associated with IA. Use of granulocyte-colony-stimulating factor showed a trend toward a protective effect (HR, 0.37; 95% CI, 0.1-31.0; P = 0.06). Relapsed AML, secondary AML, and duration of neutropenia were independent factors for determining the risk for development of IA prior to SCT. The results provide further guidance for antifungal stewardship programs when integrating individual patient tailored decision making in antifungal prophylaxis strategies.

Role of prostaglandin D2 /CRTH2 pathway on asthma exacerbation induced by Aspergillus fumigatus

Aspergillus fumigatus is often associated in asthmatic patients with the exacerbation of asthma symptoms. The pathomechanism of this phenomenon has not been fully understood. Here, we evaluated the immunological mechanisms and the role of the prostaglandin D2 / Chemoattractant Receptor-Homologous Molecule Expressed on Th2 Cells (CRTH2) pathway in the development of Aspergillus-associated asthma exacerbation. We studied the effects of A. fumigatus on airway inflammation and bronchial hyper-responsiveness in a rat model of chronic asthma. Inhalation delivery of A. fumigatus conidia increased the airway eosinophilia and bronchial hyper-responsiveness in ovalbumin-sensitized, challenged rats. These changes were associated with prostaglandin D2 synthesis and CRTH2 expression in the lungs. Direct inflammation occurred in ovalbumin-sensitized, challenged animals, whereas pre-treatment with an antagonist against CRTH2 nearly completely eliminated the A. fumigatus-induced worsening of airway eosinophilia and bronchial hyper-responsiveness. Our data demonstrate that production of prostaglandin D2 followed by eosinophil recruitment into the airways via a CRTH2 receptor are the major pathogenic factors responsible for the A. fumigatus-induced enhancement of airway inflammation and responsiveness.

Differential strain-related tissue immune response to sublethal systemic Aspergillus fumigatus infection in mice

Using a nonlethal systemic Aspergillus fumigatus infection, we have recently shown that similarly efficient elimination of fungus from spleens of prototypic Th1 (C57BL/6) and prototypic Th2 (BALB/c) mice is associated with differential immune responses. In light of these data and given the disseminated character of infection, the aim of the present study is to explore whether there are also strain-dependent differences in antifungal responses in peripheral tissues of infected mice. Although similar efficiency of conidia removal was noted in liver and kidneys of both strains, BALB/c mice seemed more prone to tissue injury. Compared with other nonlymphoid organs, lungs proved immunologically the most responsive in systemic aspergillosis. Lower numbers of neutrophils and macrophages in the lungs of infected BALB/c mice, delayed and lower (compared with C57BL/6 mice) expression of their oxidative activity, along with late IFN-γ and upregulated IL-4 production by lung cells might be responsible for slower elimination of A. fumigatus from the lungs of this mouse strain. The data obtained imply that lungs should be viewed as mandatory organ in evaluation of immune-mediated antifungal potential of drugs in models of systemic/disseminated infection and that strain differences noted in tissue responses should be taken into account in these settings.