Identification of the fungal ligand triggering cytotoxic PRR-mediated NK cell killing of Cryptococcus and Candida

Shu Shun Li,Jatin M Vyas,Michael K Mansour,Fay Munro,Christopher H Mody,Matthias Amrein,Roy A Mariuzza,Richard F Xiang,Priyanka Mukherjee,Henry Ogbomo,Lian Szabo,Stephen M Robbins

doi:10.1038/s41467-018-03014-4

Abstract

Natural killer (NK) cells use the activating receptor NKp30 as a microbial pattern-recognition receptor to recognize, activate cytolytic pathways, and directly kill the fungi Cryptococcus neoformans and Candida albicans. However, the fungal pathogen-associated molecular pattern (PAMP) that triggers NKp30-mediated killing remains to be identified. Here we show that β-1,3-glucan, a component of the fungal cell wall, binds to NKp30. We further demonstrate that β-1,3-glucan stimulates granule convergence and polarization, as shown by live cell imaging. Through Src Family Kinase signaling, β-1,3-glucan increases expression and clustering of NKp30 at the microbial and NK cell synapse to induce perforin release for fungal cytotoxicity. Rather than blocking the interaction between fungi and NK cells, soluble β-1,3-glucan enhances fungal killing and restores defective cryptococcal killing by NK cells from HIV-positive individuals, implicating β-1,3-glucan to be both an activating ligand and a soluble PAMP that shapes NK cell host immunity.

Highlights

Natural killer (NK) cells use the activating receptor NKp30 as a microbial pattern-recognition receptor to recognize, activate cytolytic pathways, and directly kill the fungi Cryptococcus neoformans and Candida albicans
We have made four major observations: 1) β-1,3-glucan bound to recombinant NKp30 and to NKp30 expressed on YT cells; 2) Blocking β-1,3-glucan synthesis in C. neoformans inhibited NK cell binding and killing of Cryptococcus; 3) β-1,3-glucan activated NK cells to increase expression of NKp30 and perforin, induced NKp30 clustering, granule polarization at the immunological synapse (IS), as well as perforin release and enhanced killing of Cryptococcus and C. albicans; and 4) β-1,3-glucan was able to restore defective NK cell cryptococcal killing from HIV-infected individuals
We had previously identified NKp30 as an Ig-like transmembrane pattern-recognition receptor (PRR) for fungi[15], and demonstrate that β-1,3-glucan is the fungal pathogen-associated molecular pattern (PAMP) for NKp30. β-glucans have been observed to protect against bacteria, virus, Candida, and parasite in experimental models[44,45,46,47,48,49], and appears to be beneficial for high-risk surgical patients[50,51,52]

Summary

Introduction

Natural killer (NK) cells use the activating receptor NKp30 as a microbial pattern-recognition receptor to recognize, activate cytolytic pathways, and directly kill the fungi Cryptococcus neoformans and Candida albicans. We demonstrated that the NK cell receptor, NKp30, is the pattern-recognition receptor (PRR) recognizing C. neoformans and C. albicans that triggers activation of PI3K and Erk 1/2, perforin release, and fungal cytotoxicity[15]. Signaling PPRs include extracellular Toll-like receptors, C-type lectin receptors, intracellular nucleotide-binding oligomerization domain-like receptors (NLR), and retinoic acid inducible gene Ilike helicase receptors (RLR)[20] In addition to these categories, a new class of PRR has been described that includes NK cellactivating receptors, NKp30, NKp46, and CD56 that bind to fungi and parasites to induce mobilization and release of cytotoxic granules that kill the pathogen[15,21,22,23]. NKp30 mediates NK cell killing of both acapsular Cryptococcus and C

Methods

Findings

Conclusion