Abstract
Extracellular vesicles (EVs) released from fungi have been shown to participate in inter-organismal communication and in cross-kingdom modulation of host defense. Malassezia species are the dominant commensal fungal members of the human skin microbiota. We have previously found that Malassezia sympodialis releases EVs. These EVs, designated MalaEx, carry M. sympodialis allergens and induce a different inflammatory cytokine response in peripheral blood mononuclear cells (PBMC) from patients with atopic dermatitis compared to healthy controls. In this study, we explored the host-microbe interaction between MalaEx and human keratinocytes with the hypothesis that MalaEx might be able to activate human keratinocytes to express the intercellular adhesion molecule-1 (ICAM-1, CD54). MalaEx were prepared from M. sympodialis (ATCC 42132) culture supernatants by a combination of centrifugation, filtration and serial ultracentrifugation. The MalaEx showed a size range of 70–580 nm with a mean of 154 nm using nanoparticle tracking analysis. MalaEx were found to induce a significant up-regulation of ICAM-1 expression on primary human keratinocytes isolated from human ex vivo skin (p = 0.026, n = 3), compared to the unstimulated keratinocytes. ICAM-1 is a counter ligand for the leukocyte integrins lymphocyte function-associated antigen-1 (LFA-1) and macrophage-1 antigen (Mac-1), of which induced expression on epithelial cells leads to the attraction of immune competent cells. Thus, the capacity of MalaEx to activate keratinocytes with an enhanced ICAM-1 expression indicates an important step in the cutaneous defense against M. sympodialis. How this modulation of host cells by a fungus is balanced between the commensal, pathogenic, or beneficial states on the skin in the interplay with the host needs to be further elucidated.
Highlights
Extracellular vesicles (EVs) are released from different mammalian cell-types and from microorganisms, parasites, and plants (Bielska et al, 2019)
The pooled batch of three MalaEx batches harvested from 48 h M. sympodialis culture supernatants had a protein content of 1.45 mg/ml
Nanoparticle-Tracking Analysis (NTA) analysis indicated that the MalaEx had a size range of 70–580 nm, with a mean of 154 nm (n = 4 video recordings) and the total particle concentration was 1.19 × 1013 particles/ml (Figure 1)
Summary
Extracellular vesicles (EVs) are released from different mammalian cell-types and from microorganisms, parasites, and plants (Bielska et al, 2019). EVs are heterogenous in size, 20 up to 1,000 nm in diameter, and their function differs depending on their cell of origin, different routes involved in biogenesis, release and their cargo (Soares et al, 2017). EVs from microorganisms, such as fungi, are usually around 100–1,000 nm, and have been associated with cytotoxicity, the invasion of host cells, and the transfer of virulence factors (Brown et al, 2015). EVs from the host have on their part been found to deliver host sRNA into fungal cells and induce crosskingdom RNA interference (RNAi) to silence fungal virulence genes (Cai et al, 2018)
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