Brucella β 1,2 Cyclic Glucan Is an Activator of Human and Mouse Dendritic Cells

Anna Martirosyan,Suzana Pinto Salcedo,Alexandre Muller,Ignacio Moriyón,Melissa Dullaers,Jean-Pierre Gorvel,Patrick Lecine,Lee Leserman,Edgardo Moreno,Marielle Mello,Jacques Banchereau,Hélène Dutartre,Sangkon Oh,Camino Pérez-Gutierrez,Gerard Zurawski,Sandy Zurawski,Eynav Klechevsky,Romain Banchereau,Yves Levy

doi:10.1371/journal.ppat.1002983

Abstract

Bacterial cyclic glucans are glucose polymers that concentrate within the periplasm of alpha-proteobacteria. These molecules are necessary to maintain the homeostasis of the cell envelope by contributing to the osmolarity of Gram negative bacteria. Here, we demonstrate that Brucella β 1,2 cyclic glucans are potent activators of human and mouse dendritic cells. Dendritic cells activation by Brucella β 1,2 cyclic glucans requires TLR4, MyD88 and TRIF, but not CD14. The Brucella cyclic glucans showed neither toxicity nor immunogenicity compared to LPS and triggered antigen-specific CD8+ T cell responses in vivo. These cyclic glucans also enhanced antigen-specific CD4+ and CD8+ T cell responses including cross-presentation by different human DC subsets. Brucella β 1,2 cyclic glucans increased the memory CD4+ T cell responses of blood mononuclear cells exposed to recombinant fusion proteins composed of anti-CD40 antibody and antigens from both hepatitis C virus and Mycobacterium tuberculosis. Thus cyclic glucans represent a new class of adjuvants, which might contribute to the development of effective antimicrobial therapies.

Highlights

Cyclic glucans are intrinsic components of the envelopes of Gram negative bacteria such as Agrobacterium, Rhizobium, Ralstonia solanacearum, Xanthomonas campestris, Rhodobacter sphaeroides and Brucella spp. [1]
The periplasmic cyclic glucan is required for B. abortus intracellular trafficking [4,5,6] through the recruitment of the raft protein flotilin-1 at the site of the Brucella-containing vacuole [6]
We show that bacterial cyclic b-glucans can be used to enhance cellular immunity by activation of dendritic cells, from both mice and humans

Summary

Introduction

Cyclic glucans are intrinsic components of the envelopes of Gram negative bacteria such as Agrobacterium, Rhizobium, Ralstonia solanacearum, Xanthomonas campestris, Rhodobacter sphaeroides and Brucella spp. [1]. The periplasmic cyclic glucan is required for B. abortus intracellular trafficking [4,5,6] through the recruitment of the raft protein flotilin-1 at the site of the Brucella-containing vacuole [6]. This polysaccharide is built of a cyclic backbone of 17 to 25 glucose units in b-1,2 linkages (CbG). If the CbG content of a single bacterium is released inside a Brucella-containing vacuole, its concentration in the vacuole can reach 10 mM. The release of CbG in mM concentration upon bacterial killing through immune mechanisms [6] might alter the host immune responses

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