Differential innate immune responses of human macrophages and bronchial epithelial cells against Talaromyces marneffei

Abstract

Abstract third-party references: This work was supported by the General Research Fund (No. 17104318), Research Grants Council, University Grants Committee, Hong Kong; Health and Medical Research Fund (No. HKM-15-M07 [commissioned project]), Food and Health Bureau, Government of the Hong Kong Special Administrative Region, Hong Kong; Seed Fund for Basic Research, The University of Hong Kong, Hong Kong; as well as the Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, Ministry of Education, China. We thank Dr PJ Punt and Dr ML Yeung for generously providing us the plasmids pAN7-1 and pEGFP-C1, respectively. We are also grateful to the staff members from the Centre for Genomic Sciences and Faculty Core Facility of Li Ka Shing Faculty of Medicine, The University of Hong Kong, for their technical support in RNA–Seq and image analyses, respectively. Background: Talaromyces marneffei is a thermally dimorphic fungal pathogen endemic in Southeast Asia. As inhalation of airborne conidia is believed as the major infection route, airway epithelial cells followed by pulmonary macrophages are the first cell types which the fungus encounters inside the host. However, there is a lack of knowledge on how the fungus interacts with host cells during infection. Materials/methods: Human peripheral blood-derived macrophages (hPBDMs) cultured with the supplementation of autologous plasma were used as the in vitro infection model for the study of innate immune response to T. marneffei infection. Transcriptomic changes of hPBDMs upon infection were profiled by RNA–sequencing and mRNA expression changes in immune-related genes were confirmed by reverse-transcription–quantitative polymerase chain reaction (qRT–PCR). Differential cytokine responses in human bronchial epithelial cells (hBECs) were also determined and compared to macrophages. A green fluorescent protein-tagged T. marneffei strain (GFP-PM1) was constructed to visualise the interactions between T. marneffei and hBECs using confocal microscopy and live cell imaging. Results: T. marneffei infection could activate hPBDMs to the M1-like phenotype and trigger a potent induction of chemokine (CXCL8, CXCL10, CCL5 and CCL20) and pro-inflammatory cytokine (TNF) production as well as the expression of other immunoregulatory genes (SOD2, CCL3, STAT1, CLEC4E, IL1B, IER3, PIK3R2 and C3). In contrast to hPBDMs, there was no detectable innate cytokine response (CXCL8, CXCL10, IFNA2, IFNB1, IFNL1, IFNL2, IL1B, IL6, and TNF mRNA expression) against T. marneffei in hBECs. Under confocal microscopy, internalisation of T. marneffei by hBECs was confirmed. Live cell imaging further demonstrated that the infected cells exhibited normal cellular physiology, especially that the process of cell division could be observed. Conclusions: Our results illustrated a potential role of hBECs to serve as reservoir cells for T. marneffei to evade immunosurveillance by phagocytes, from which the fungus reactivates when the host immunity is weakened and causes infection. Such immunoevasion and reactivation may also help explain the long incubation period observed for talaromycosis, in particular the travel-related cases.