Innate Immunity to the Pathogenic Fungus Coccidioides posadasii Is Dependent on Toll-Like Receptor 2 and Dectin-1

Abstract

Coccidioides posadasii is a pathogenic fungus that causes endemic and epidemic coccidioidomycosis in the deserts of North, Central, and South America. How the innate immune system responds to the organism is not well understood. Here we show that elicited mouse peritoneal macrophages respond to spherules (the tissue form of the fungus) by producing proinflammatory cytokines as measured by quantitative PCR of cellular transcripts and by enzyme-linked immunosorbent assay (ELISA) assays for secreted protein. We examined the contribution of Toll-like receptors (TLR) and MyD88 in macrophage responses to formalin-killed spherules (FKS) by comparing cytokine responses of elicited macrophages from different knockout mice. FKS were added to elicited mouse peritoneal macrophages from wild-type, TLR2؊/؊ , and MyD88 ؊/؊ cells, and wild-type cells made more tumor necrosis factor alpha, MIP-2, and interleukin 6 than did the mutant macrophages. In contrast, the C3H/HeJ mice, which have a point mutation in TLR4, and TLR4 ؊/؊ B6 mice exhibited no defect in cytokine production compared to the control mice. We also investigated the role of the macrophage ␤-glucan receptor, Dectin-1. RAW 264.7 macrophages overexpressing Dectin-1 produced more cytokines in respond to FKS, live spherules, and purified ␤-glucan than did control RAW cells. Blockage of Dectin-1 with antibodies inhibited cytokine production in elicited mouse peritoneal macrophages. Taken together, these results show that cytokine responses in mouse peritoneal macrophages to C. posadasii spherules are dependent on TLR2, MyD88, and Dectin-1.

Dectin-1 and TLRs Permit Macrophages to Distinguish between Different Aspergillus fumigatus Cellular States

“…Results did not differ in experiments using bone marrow-derived macrophages (data not shown). The data emphasize the importance of dectin-1 in mediating inflammatory responses to inhaled fungal pathogens, because this receptor is now implicated in recognition of the filamentous fungus, A. fumigatus, as well as P. carinii and C. posadasii spherules (15,16,20,21). Inhalation of resting Aspergillus spores is common and constant, and a robust inflammatory response in the absence of a real threat could be disruptive to the airway.…”

“…Dectin-1 mediates macrophage internalization of and activation by glucan-containing particles, including zymosan, C. albicans yeasts, Pneumocystis carinii, and Coccidioides posadasii spherules (15,16,20,21). We determined the role of dectin-1 in mediating murine macrophage responses to Aspergillus using laminarin (a soluble ␤-glucan) or anti-dectin-1 polyclonal Ab, which specifically blocks the receptor (13,14,16).…”

Enhanced Immunogenicity of a Tricomponent Mannan Tetanus Toxoid Conjugate Vaccine Targeted to Dendritic Cells via Dectin-1 by Incorporating β-Glucan

“…Dectin-1 is a pattern-recognition receptor that has been implicated in defending against invasions by C. albicans (18)(19)(20), Aspergillus (21), Coccidioides (22), and Pneumocystis (23). This receptor is a single transmembrane protein with a carbohydrate recognition domain in its extracellular region that binds b-1,3-glucan (a major component of the cell wall of a variety of fungal pathogens), a transmembrane segment, and an N terminus cytosolic domain.…”

Immunological Actions of Sophy β‐Glucan (β‐1,3‐1,6 Glucan), Currently Available Commercially as a Health Food Supplement

“…Thus, Dectin-1 is thought to be the main β-glucan receptor involved in innate and adaptive immune responses to foreign antigens and pathogens, including β-glucan as an immune function stimulator. In addition, several reports revealed that Dectin-1 cooperates with pattern recognition receptors (PRRs) and Toll-like receptors (TLRs) in the innate immune responses to β-glucan recognition (13,43). These findings have prompted new interest in the interaction of β-glucan with its receptor (Dectin-1) or TLRs as co-receptors at the basic and clinical levels of medical research and immune therapeutics.…”