Supporting Data for the Study of Interactions between Talaromyces marneffei and host airway epithelial cells upon infection

This file contains results of histology, confocal microscopy, RNA-seq and the downstream bioinformatic analysism, as well as flow cytometry for the validation of a newly established cell model and its transcriptomic profile during an Talaromcyes marneffei infection.

Talaromyces marneffei is a thermally dimorphic fungus known to be the causative pathogen of talaromycosis - a potentially fatal fungal infection typically found in immunocompromised individuals. In accordance with the proposed transmission model, the airborne fungal conidia are believed to be the vector of transmission targeting the human respiratory tract. Although the details about the life cycle and pathogenesis of T. marneffei have yet to be delineated, the fungus has been shown to survive clearance by innate immune cells and is speculated to establish latency in the host for subsequent reactivation. This study, therefore, speculated that the epithelial cells are the latency reservoir in the body for their predominance in the airway and their non-immunological lineage. 

Based on this speculation, it is further hypothesized that the airway epithelial cells are immunologically inert to Talaromyces marneffei infection. To provide a physiologically relevant environment for the hypothesis, an in vitro airway epithelium model composed of ciliated cells, goblet cells, and basal cells was developed out of the human immortalized bronchial epithelial cell line 16HBE14o- and morphologically validated by histology and confocal microscopy. T. marneffei infection was then performed in the cell model and the resultant infection rate was found to be approximately 10% at a multiplicity of infection of 20 by flow cytometry, which is significantly improved from the 1.5% in the undifferentiated 16HBE14o-. Additionally, the flow cytometry histogram and the 3D z-stack confocal image of the infected cell model both hinted that an unidentified subpopulation in the cell model is likely to be more susceptible to T. marneffei infection. Following the study of infection rate, the model infected with the fungus was subjected to RNA-sequencing to obtain its transcriptomic profile during the infection. Subsequent differential expression analysis showed that a total of 51 upregulated genes and 169 downregulated genes were identified using the threshold of Log2(Fold Change) < 1 or > - 1 and p-value < 0.05. More specifically, the differentially expressed genes (DEGs) associated with antimicrobial responses were all found to be downregulated. All the DEGs were further subjected to various analyses including biological process enrichment analysis, pathway enrichment analysis, k-mean clustering, protein enrichment analysis, and spearman’s correlation analysis to investigate the pathways and biological processes they regulate. By combining the results of all the bioinformatics analyses, it appears that the fungus can create an immunosuppression state in the epithelium model during the infection by downregulating the TLR/MAPK pathway, and more precisely, both the MyD88-dependent pathway and the MyD88-independent pathway along with the transcription factor AP-1 to suppress the expression of the two cytokines known to be associated with T. marneffei infection – interleukin 6 and interleukin 8. At last, the use of a novel epithelium model shortlisted the immunological pathways and processes downregulated by T. marneffei during infection, providing experimental evidence supporting the idea that the fungus can exploit the airway epithelial cells as the reservoir in the body to evade immunosurveillance for the establishment of prolonged infection.