Synergy between Ficolin-2 and Pentraxin 3 Boosts Innate Immune Recognition and Complement Deposition

Ying Jie Ma,Andrea Doni,Tina Hummelshøj,Christian Honoré,Antonio Bastone,Alberto Mantovani,Nicole M Thielens,Peter Garred

doi:10.1074/jbc.m109.009225

Abstract

The long pentraxin 3 (PTX3) is a multifunctional soluble pattern recognition molecule that is crucial in innate immune protection against opportunistic fungal pathogens such as Aspergillus fumigatus. The mechanisms that mediate downstream effects of PTX3 are largely unknown. However, PTX3 interacts with C1q from the classical pathway of the complement. The ficolins are recognition molecules of the lectin complement pathway sharing structural and functional characteristics with C1q. Thus, we investigated whether the ficolins (Ficolin-1, -2, and -3) interact with PTX3 and whether the complexes are able to modulate complement activation on A. fumigatus. Ficolin-2 could be affinity-isolated from human plasma on immobilized PTX3. In binding studies, Ficolin-1 and particularly Ficolin-2 interacted with PTX3 in a calcium-independent manner. Ficolin-2, but not Ficolin-1 and Ficolin-3, bound A. fumigatus directly, but this binding was enhanced by PTX3 and vice versa. Ficolin-2-dependent complement deposition on the surface of A. fumigatus was enhanced by PTX3. A polymorphism in the FCN2 gene causing a T236M amino acid change in the fibrinogen-like binding domain of Ficolin-2, which affects the binding to GlcNAc, reduced Ficolin-2 binding to PTX3 and A. fumigatus significantly. These results demonstrate that PTX3 and Ficolin-2 may recruit each other on pathogens. The effect was alleviated by a common amino acid change in the fibrinogen-like domain of Ficolin-2. Thus, components of the humoral innate immune system, which activate different complement pathways, cooperate and amplify microbial recognition and effector functions.

Highlights

C-terminal fibrinogen-like (FBG) domain involved in innate immune defense [1, 2]
Reduced Ficolin-2 T236M Binding to GlcNAc, pentraxin 3 (PTX3), and A. fumigatus—Previously we found an allelic variant in the FCN2 gene that replaced a threonine with a methionine at amino acid position 236 (Ficolin-2 T236M), which when purified from serum exhibited reduced binding capacity to GlcNAc compared with wild type Ficolin-2 [10]
We have demonstrated that circulating plasma-derived Ficolin-2 interacted with immobilized PTX3 in affinity chromatography experiments

Summary

Introduction

C-terminal fibrinogen-like (FBG) domain involved in innate immune defense [1, 2]. In humans, three types of ficolins have been identified as follows: Ficolin-1 (M-ficolin), Ficolin-2 (L-ficolin), and Ficolin-3 (H-ficolin/Hakata antigen). Binding of Ficolin-1, -2, and -3 to A. fumigatus—A. fumigatus conidia were washed and resuspended in 100 ␮l of HEPES buffer containing 1% heat-inactivated FCS at 2.4 ϫ 107 cells/ml and incubated with Ficolin-1, -2, or -3 at 37 °C for 1 h.

Results

Conclusion