Immune Modulation Mediated by Cryptococcal Laccase Promotes Pulmonary Growth and Brain Dissemination of Virulent Cryptococcus neoformans in Mice

Yafeng Qiu,Peter R Williamson,Daniel L Meister,Michal A Olszewski,John J Osterholzer,Michael J Davis,Jeremy K Dayrit,Zachary Hadd,Combes Valery

doi:10.1371/journal.pone.0047853

Abstract

C. neoformans is a leading cause of fatal mycosis linked to CNS dissemination. Laccase, encoded by the LAC1 gene, is an important virulence factor implicated in brain dissemination yet little is known about the mechanism(s) accounting for this observation. Here, we investigated whether the presence or absence of laccase altered the local immune response in the lungs by comparing infections with the highly virulent strain, H99 (which expresses laccase) and mutant strain of H99 deficient in laccase (lac1Δ) in a mouse model of pulmonary infection. We found that LAC1 gene deletion decreased the pulmonary fungal burden and abolished CNS dissemination at weeks 2 and 3. Furthermore, LAC1 deletion lead to: 1) diminished pulmonary eosinophilia; 2) increased accumulation of CD4+ and CD8+ T cells; 3) increased Th1 and Th17 cytokines yet decreased Th2 cytokines; and 4) lung macrophage shifting of the lung macrophage phenotype from M2- towards M1-type activation. Next, we used adoptively transferred CD4+ T cells isolated from pulmonary lymph nodes of mice infected with either lac1Δ or H99 to evaluate the role of laccase-induced immunomodulation on CNS dissemination. We found that in comparison to PBS treated mice, adoptively transferred CD4+ T cells isolated from lac1Δ-infected mice decreased CNS dissemination, while those isolated from H99-infected mice increased CNS dissemination. Collectively, our findings reveal that immune modulation away from Th1/Th17 responses and towards Th2 responses represents a novel mechanism through which laccase can contribute to cryptococcal virulence. Furthermore, our data support the hypothesis that laccase-induced changes in polarization of CD4+ T cells contribute to CNS dissemination.

Highlights

Cryptococcus neoformans (C. neoformans) is a leading cause of fatal mycosis worldwide in individuals with impaired T cell function [1,2]
We found that in comparison to PBS treated mice, adoptively transferred CD4+ T cells isolated from lac1D-infected mice decreased central nervous system (CNS) dissemination, while those isolated from H99-infected mice increased CNS dissemination
Consistent with previous data obtained with other cryptococcal strains or murine backgrounds, no CNS dissemination of the lac1D strain was observed in contrast with a massive dissemination of H99 (Figure 1B)

Summary

Introduction

Cryptococcus neoformans (C. neoformans) is a leading cause of fatal mycosis worldwide in individuals with impaired T cell function [1,2]. To combat CNS dissemination, cell-mediated immune responses, especially Th1 polarization and robust expression of IFN-c, are required [4,5,6,7,8,9,10]. Studies have demonstrated that Th2 adaptive immune responses are non-protective [5,11,12,13]. The role of Th17 is less known, but most studies demonstrate that it can positively contribute to protection of the C. neoformansinfected host [14,15,16]. Interleukin 17A (IL-17A), a key cytokine produced by Th17 cell lineage, may itself contribute to anti-cryptococcal lung defenses [17]. The Th2 cytokines, IL-4 and IL-13, promote cryptococcal lung infection [15,16,18,19].

Objectives

Methods

Results

Conclusion