CR3 and Dectin-1 Collaborate in Macrophage Cytokine Response through Association on Lipid Rafts and Activation of Syk-JNK-AP-1 Pathway.

Juin-Hua Huang,Gordon D Brown,Ching-Yu Lin,Sheng-Yang Wu,Wen-Yu Chen,Chih-Pin Chuu,Betty A Wu-Hsieh,Ching-Liang Chu,Sarah L Gaffen

doi:10.1371/journal.ppat.1004985

Abstract

Collaboration between heterogeneous pattern recognition receptors (PRRs) leading to synergistic coordination of immune response is important for the host to fight against invading pathogens. Although complement receptor 3 (CR3) and Dectin-1 are major PRRs to detect fungi, crosstalk between these two receptors in antifungal immunity is largely undefined. Here we took advantage of Histoplasma capsulatum which is known to interact with both CR3 and Dectin-1 and specific particulate ligands to study the collaboration of CR3 and Dectin-1 in macrophage cytokine response. By employing Micro-Western Array (MWA), genetic approach, and pharmacological inhibitors, we demonstrated that CR3 and Dectin-1 act collaboratively to trigger macrophage TNF and IL-6 response through signaling integration at Syk kinase, allowing subsequent enhanced activation of Syk-JNK-AP-1 pathway. Upon engagement, CR3 and Dectin-1 colocalize and form clusters on lipid raft microdomains which serve as a platform facilitating their cooperation in signaling activation and cytokine production. Furthermore, in vivo studies showed that CR3 and Dectin-1 cooperatively participate in host defense against disseminated histoplasmosis and instruct adaptive immune response. Taken together, our findings define the mechanism of receptor crosstalk between CR3 and Dectin-1 and demonstrate the importance of their collaboration in host defense against fungal infection.

Highlights

Diseases caused by fungal pathogens have become an important cause of morbidity and mortality over the last decades due to the increasing number of immunocompromised patients [1]
By use of blocking antibodies we previously showed that macrophage utilizes complement receptor 3 (CR3) to phagocytose and both CR3 and Dectin-1 to mediate cytokine response to H. capsulatum [13]
Employing Itgam-/, Clec7a-/, and Itgam-/-Clec7a-/- macrophages here we investigated the mechanism of receptor crosstalk between CR3 and Dectin-1 (S1A Fig)

Summary

Introduction

Diseases caused by fungal pathogens have become an important cause of morbidity and mortality over the last decades due to the increasing number of immunocompromised patients [1]. To reveal the cellular and molecular mechanisms of the interaction between host and fungal pathogens will be helpful for the development of new therapeutic strategies. Innate immune cells recognize pathogen-associated molecular patterns (PAMPs) on fungi through pattern recognition receptors (PRRs) [2, 3]. The fungal cell wall is composed predominantly of glucans, chitin, mannose and other covalently-linked proteins with the composition varies between species and even between the different strains and morphological forms of the same species [4, 5]. Since a single pathogen is composed of multiple PAMPs, innate immune cells are likely to simultaneously or sequentially utilize a complex set of PRRs to interact with a specific pathogen. The coordination between PRRs leading to activation or inhibition of downstream signaling is referred to as “receptor crosstalk” [6]

Methods

Results

Conclusion