Neutrophils Increase or Reduce Parasite Burden in Trypanosoma cruzi-Infected Macrophages, Depending on Host Strain: Role of Neutrophil Elastase

Tatiana Luna-Gomes,Alexandre Morrot,Hugo C Castro-Faria-Neto,Debora Decote-Ricardo,Alessandra A Filardy,Isabel Ferreira Larocque-De-Freitas,Patrícia T Bozza,George A Dosreis,Célio G Freire-De-Lima,Juliana Dutra B Rocha,Marise P Nunes,Cristina Bonorino

doi:10.1371/journal.pone.0090582

Abstract

Neutrophils are involved in the initial steps of most responses to pathogens and are essential components of the innate immune response. Due to the ability to produce and release various soluble mediators, neutrophils may participate in the regulation of the inflammatory response. Little is known about the role of neutrophils during protozoan infections including infection by Trypanosoma cruzi. In the present study we investigated the importance of inflammatory neutrophils on macrophage activation and T. cruzi replication in vitro, in cells obtained from BALB/c mice and C57Bl/6 mice. Co-cultures of BALB/c apoptotic or live neutrophils with infected peritoneal macrophages resulted in increased replication of the parasites and in the production of TGF-β and PGE2. The treatment with anti-TGF-β neutralizing antibody and COX inhibitor blocked the parasite replication in vitro. On the other hand, co-cultures of T. cruzi infected macrophages with live neutrophils isolated from C57BL/6 mice resulted in decreased number of trypomastigotes in culture and increased production of TNF-α and NO. The addition of anti-TNF-α neutralizing antibody or elastase inhibitor resulted in the abolishment of macrophage microbicidal effect and increased parasite replication. Addition of elastase to infected macrophages reduced the replication of the parasites, and on the other hand, addition of a selective inhibitor of iNOS increased parasite growth, suggesting the role of NO in this system. Our findings reveal that neutrophils may regulate T. cruzi experimental infection and determine susceptibility and resistance to infection.

Highlights

Neutrophils are among the first cells to be recruited to the infection site and are important in controlling the host defense through oxidant and protease-dependent mechanisms [1,2,3]
Live or apoptotic inflammatory neutrophils were co-cultured with T. cruzi clone Dm28c infected macrophages from BALB/c or C57BL/6 mice, susceptible and resistant model to infection with T. cruzi clone Dm28c respectively
In vitro analysis of the effects of neutrophils on T. cruzi infected macrophages revealed that either apoptotic or live neutrophils markedly exacerbated T. cruzi replication in BALB/c macrophages (Figure 1a), but inflammatory neutrophils almost eliminated T. cruzi when co-cultured with C57BL/6 macrophages, in strainspecific effects (Figure 1b)

Summary

Introduction

Neutrophils are among the first cells to be recruited to the infection site and are important in controlling the host defense through oxidant and protease-dependent mechanisms [1,2,3]. These cells provide an important link between innate and adaptive immunity during parasite infections [4,5]. Inflammatory neutrophils secrete proteases, chemokines and soluble mediators that regulate inflammation. Activated neutrophils have a short lifespan and undergo constitutive apoptosis, leading to their phagocytic removal by macrophages [6,7]. Cells undergoing apoptosis expose ligands for a set of conserved receptors on macrophage surfaces

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Conclusion