Depletion of Neutrophils Exacerbates the Early Inflammatory Immune Response in Lungs of Mice Infected with Paracoccidioides brasiliensis.

Paula Andrea Pino-Tamayo,Damaris Lopera,Juan David Puerta-Arias,Martha Eugenia Urán-Jiménez,Ángel González

doi:10.1155/2016/3183285

Abstract

Neutrophils predominate during the acute phase of the Paracoccidioides brasiliensis infection. Herein, we determined the role of the neutrophil during the early stages of experimental pulmonary paracoccidioidomycosis using a monoclonal antibody (mAb) specific for neutrophils. Male BALB/c mice were inoculated intranasally with 1.5 × 106 or 2 × 106 P. brasiliensis yeast cells. The mAb was administered 24 h before infection, followed by doses every 48 h until mice were sacrificed. Survival time was evaluated and mice were sacrificed at 48 h and 96 h after inoculation to assess cellularity, fungal load, cytokine/chemokine levels, and histopathological analysis. Neutrophils from mAb-treated mice were efficiently depleted (99.04%). Eighty percent of the mice treated with the mAb and infected with 1.5 × 106 yeast cells died during the first two weeks after infection. When mice were treated and infected with 2 × 106 yeast cells, 100% of them succumbed by the first week after infection. During the acute inflammatory response significant increases in numbers of eosinophils, fungal load and levels of proinflammatory cytokines/chemokines were observed in the mAb-treated mice. We also confirmed that neutrophils are an important source of IFN-γ and IL-17. These results indicate that neutrophils are essential for protection as well as being important for regulating the early inflammatory immune response in experimental pulmonary paracoccidioidomycosis.

Highlights

Neutrophils have been considered to be crucial players in immune defense against bacterial and fungal pathogens
In order to investigate the efficiency of the monoclonal antibody (mAb) anti-Ly6G to deplete neutrophils in BALB/c mice inoculated with phosphate-buffered saline (PBS) or 1.5×106 P. brasiliensis yeast cells, a flow cytometry assay was carried out for lung homogenates at 48 h and 96 h after inoculation
We observed that 80% of neutrophildepleted mice infected with 1.5 × 106 yeast cells died within 2 weeks of infection; interestingly, when mice were infected with a slightly larger inoculum containing 2 × 106 yeast cells, 100% of neutrophil-depleted animals succumbed by the first week postinfection, while most of the untreated or isotype-treated animals survived the 12-week assessment period (Figure 1(c))

Summary

Introduction

Neutrophils have been considered to be crucial players in immune defense against bacterial and fungal pathogens They participate as the first line of innate immunity and as effectors of adaptive immunity, contributing to the development of inflammatory reactions [1, 2]. These cells exert mechanisms of defense, such as phagocytosis [3, 4], intracellular, and extracellular pathogen destruction by chemical means [4, 5], neutrophil extracellular traps (NETs) formation [4, 6], and the production of numerous cytokines, chemokines, and growth factors [7, 8] used to defeat microbial pathogens [4, 9].

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