A unique biofilm in human deep mycoses: fungal amyloid is bound by host serum amyloid P component

Background/Objectives We have demonstrated the presence of Candida cell surface amyloids that are important in aggregation of fungi and adherence to tissue. Fungal amyloid was present in invasive human candidal infections and host serum amyloid P component (SAP) bound to the fungal amyloid. SAP is a protease-resistant glycoprotein that binds avidly to amyloid and interferes with host defence, especially against bacterial pathogens for which neutrophils are important. In this study, we investigated whether biofilm of fungal amyloid and SAP was a feature of other disseminated fungal infections. Methods Tissue specimens from 15 autopsies were systematically evaluated with multiple histochemical stains including thioflavin T and Congo red (dyes that stain amyloid), as well as antibody to SAP. We studied specimens with disseminated aspergillosis, mucormycosis and coccidioidomycosis. The structure of the lesions, host inflammatory cells and the presence of fungal amyloid and SAP were determined. Results The structure of the lesions was characteristic in aspergillosis (‘starburst’) and mucormycosis (closely apposed bundles of hyphae). Host inflammatory cells were absent or few in number within these lesions. In Coccidioides lesions, host inflammation was sparse as well. Fungal amyloid was a prominent feature of all lesions along with abundant SAP bound to hyphae and spherules. Fungal amyloid and SAP perhaps contributed to persistence in caseous necrosis lesions. SAP also bound to Aspergillus and Mucorales amyloid in vitro. Conclusions A biofilm including amyloid and SAP is present in invasive fungal infections. This biofilm may dampen host defence leading to the characteristic sparse inflammatory reaction found in these infections

Peptide Detection of Fungal Functional Amyloids in Infected Tissue

Many fungal cell adhesion proteins form functional amyloid patches on the surface of adhering cells. The Candida albicans Agglutinin-like sequence (Als) adhesins are exemplars for this phenomenon, and have amyloid forming sequences that are conserved between family members. The Als5p amyloid sequence mediates amyloid fibril formation and is critical for cell adhesion and biofilm formation, and is also present in the related adhesins Als1p and Als3p. We have developed a fluorescent peptide probe containing the conserved Als amyloid-forming sequence. This peptide bound specifically to yeast expressing Als5p, but not to cells lacking the adhesin. The probe bound to both yeast and hyphal forms of C. albicans. Δals1/Δals3 single and double deletion strains exhibited reduced fluorescence, indicating that probe binding required expression of these proteins. Additionally, the Als peptide specifically stained fungal cells in abscesses in autopsy sections. Counterstaining with calcofluor white showed colocalization with the amyloid peptide. In addition, fungi in autopsy sections derived from the gastrointestinal tract showed colocalization of the amyloid-specific dye thioflavin T and the fluorescent peptide. Collectively, our data demonstrate that we can exploit amyloid sequence specificity for detection of functional amyloids in situ

Medical image of the week: hepatocellular carcinoma with pulmonary metastasis

A 58-year-old man with a history of hepatitis-C, liver cirrhosis and hepatocellular carcinoma treated with sorafenib and chemoembolization was admitted with septic shock due to spontaneous bacterial peritonitis with concomitant hemorrhage and acute renal failure. The patient did not respond to broad-spectrum antibiotics, aggressive care with multiple vasopressors and ventilatory support and died shortly after admission. An autopsy was performed revealing hepatocellular carcinoma with extensive intra-abdominal and thoracic metastasis

Serum Amyloid P Component and Systemic Fungal Infection: Does It Protect the Host or Is It a Trojan Horse?

It is a striking observation that tissue of patients invaded by the deep mycoses often lacks evidence of an inflammatory response. This lack of host response is often attributed to neutropenia secondary to chemotherapy. However, systematic studies do not support this simplistic explanation. However, invasive fungal lesions are characterized by abundant fungal functional amyloid, which in turn is bound by serum amyloid P component (SAP). We postulate that SAP is important in the local immune response in invasive fungal infections. The interaction between fungal functional amyloid, SAP, and the immune response in deep mycoses is discussed.Open Access Journal.This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Als5p expressing S. cerevisiae cells stained with fluorescent peptides.

<p><i>S. cerevisiae</i> harboring an empty vector (A,C) or expressing Als5p (B, D) were stained with amyloid peptide (200 µg/ml; A, B) or a scrambled-sequence peptide of identical composition (200 µg/ml; C, D). Lower micrographs are bright field images. All scale bars are 30 µm.</p

Peptide staining of <i>als1/als1 als3/als3</i> deletion strains.

<p>All strains were induced to form hyphae by incubating overnight in spider media at 37^°C. A) CAI4 and B) <i>als1/als1 als3/als3</i> double deletion strains were probed with 20 µg/ml amyloid peptide with their corresponding brightfield images (right). All scale bars are 40 µm. C) Quantification of the average intensity of images A and B. Error bars represent standard error of the mean (n = 4; see text for details).</p

Confocal micrographs of <i>C. albicans</i> yeast and hyphae binding Als5p peptide.

<p><i>C. albicans</i> cultured in spider medium, with 20 µg/ml (A, C) amyloid or (B, D) scrambled sequence peptide. Fields were imaged containing (A, B) yeast or (C, D) hyphae at a gain of 6.5. Inset images in A and B were acquired at a higher gain of 7.0.</p