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Engagement of Penicillium marneffei conidia with multiple pattern recognition receptors on human monocytes
Yuttana Srinoulprasert1, Piyapong Pongtanalert, Runglawan Chawengkirttikul
1Department of Microbiology, Faculty of Science, Mahidol University, Rama VI Road, Bangkok 10400, Thailand.
Abstract:
P. marneffei is a thermal dimorphic fungus which causes penicilliosis, an opportunistic infection in immunocompromised patients in South and Southeast Asia. Little is known about the innate immune response to P. marneffei infection. Therefore, the initial response of macrophages to P. marneffei conidia was evaluated by us. Adhesion between monocytes from healthy humans and fungal conidia was examined and found to be specifically inhibited by MAbs against PRR, such as MR, (TLR)1, TLR2, TLR4, TLR6, CD14, CD11a, CD11b, and CD18. To study the consequences of these interactions, cytokines were also examined by ELISA. Binding of P. marneffei conidia to monocytes was significantly inhibited, in a dose-dependent manner, by MAbs against MR, TLR1, TLR2, TLR4, TLR6, CD14, CD11b and CD18. When monocytes were co-cultured with the conidia, there was an increase in the amount of surface CD40 and CD86 expression, together with TNF-alpha and IL-1beta production, compared to unstimulated controls. In assays containing anti-TLR4 or anti-CD14 antibody, reduction in the amount of TNF-alpha released by monocytes stimulated with P. marneffei conidia was detected. In addition, it was found that production of TNF-alpha and IL-1beta from adherent peripheral blood monocytes was partially impaired when heat-inactivated autologous serum, in place of untreated autologous serum, was added to the assay. These results demonstrate that various PRR on human monocytes participate in the initial recognition of P. marneffei conidia, and the engagement of PRR could partly initiate proinflammatory cytokine production.
Insights
Human monocytes use pattern recognition receptors (PRRs) like mannose receptor (MR) and Toll-like receptors (TLRs) to detect P. marneffei fungi. This interaction triggers the release of inflammatory cytokines, crucial for the innate immune response.
Area of Science:
- Immunology
- Mycology
- Infectious Diseases
Background:
- Penicilliosis, caused by the fungus P. marneffei, is an opportunistic infection affecting immunocompromised individuals, particularly in South and Southeast Asia.
- The innate immune mechanisms governing the host's initial response to P. marneffei infection remain incompletely understood.
Purpose of the Study:
- To investigate the early innate immune response of human macrophages to P. marneffei conidia.
- To identify the specific pattern recognition receptors (PRRs) involved in monocyte adhesion and activation upon encountering P. marneffei.
Main Methods:
- Monocyte adhesion assays using fungal conidia and monoclonal antibodies (MAbs) targeting various PRRs, including mannose receptor (MR), Toll-like receptors (TLRs) 1, 2, 4, 6, CD14, CD11a, CD11b, and CD18.
- Cytokine analysis (TNF-alpha, IL-1beta) using ELISA and assessment of surface marker expression (CD40, CD86) via flow cytometry.
- Experiments involving heat-inactivated serum and blocking antibodies (anti-TLR4, anti-CD14) to elucidate the role of specific PRRs and serum components.
Main Results:
- Monocyte binding to P. marneffei conidia was significantly inhibited by MAbs against MR, TLR1, TLR2, TLR4, TLR6, CD14, CD11b, and CD18, indicating specific PRR involvement.
- Co-culture of monocytes with conidia led to increased CD40 and CD86 expression and elevated production of TNF-alpha and IL-1beta.
- Inhibition of TLR4 or CD14 reduced TNF-alpha release, and impaired serum components partially reduced cytokine production, highlighting the contribution of PRRs and serum factors.
Conclusions:
- Multiple PRRs on human monocytes are critical for the initial recognition and adhesion of P. marneffei conidia.
- Engagement of these PRRs partly initiates pro-inflammatory cytokine production, contributing to the early innate immune response against P. marneffei.
