Mycobacterium tuberculosis Drives Expansion of Low-Density Neutrophils Equipped With Regulatory Activities.

Marco Pio La Manna,Bartolo Tamburini,Antonio Cascio,Francesco Dieli,Valentina Orlando,Elvezia Maria Paraboschi,Paola Di Carlo,Nadia Caccamo,Rosanna Asselta

doi:10.3389/fimmu.2019.02761

Abstract

In human tuberculosis (TB) neutrophils represent the most commonly infected phagocyte but their role in protection and pathology is highly contradictory. Moreover, a subset of low-density neutrophils (LDNs) has been identified in TB, but their functions remain unclear. Here, we have analyzed total neutrophils and their low-density and normal-density (NDNs) subsets in patients with active TB disease, in terms of frequency, phenotype, functional features, and gene expression signature. Full-blood counts from Healthy Donors (H.D.), Latent TB infected, active TB, and cured TB patients were performed. Frequency, phenotype, burst activity, and suppressor T cell activity of the two different subsets were assessed by flow cytometry while NETosis and phagocytosis were evaluated by confocal microscopy. Expression analysis was performed by using the semi-quantitative RT-PCR array technology. Elevated numbers of total neutrophils and a high neutrophil/lymphocyte ratio distinguished patients with active TB from all the other groups. PBMCs of patients with active TB disease contained elevated percentages of LDNs compared with those of H.D., with an increased expression of CD66b, CD33, CD15, and CD16 compared to NDNs. Transcriptomic analysis of LDNs and NDNs purified from the peripheral blood of TB patients identified 12 genes differentially expressed: CCL5, CCR5, CD4, IL10, LYZ, and STAT4 were upregulated, while CXCL8, IFNAR1, NFKB1A, STAT1, TICAM1, and TNF were downregulated in LDNs, as compared to NDNs. Differently than NDNs, LDNs failed to phagocyte live Mycobacterium tuberculosis (M. tuberculosis) bacilli, to make oxidative burst and NETosis, but caused significant suppression of antigen-specific and polyclonal T cell proliferation which was partially mediated by IL-10. These insights add a little dowel of knowledge in understanding the pathogenesis of human TB.

Highlights

Neutrophils are the most abundant cellular type of white blood cells in the body, and they should be considered to play a role in the first line of defense against infection
Neutrophils contribute to the immune response to M. tuberculosis infection and their numbers and functions positively correlate with the active disease stage in humans
In highly susceptible M. tuberculosis mouse strains, the pharmacological interference with neutrophil-associated inflammation or their depletion resulted in reduced pathology, increased survival rates and, less mycobacterial burden [25]

Summary

INTRODUCTION

Neutrophils are the most abundant cellular type of white blood cells in the body, and they should be considered to play a role in the first line of defense against infection. In vivo mice studies have demonstrated the presence of neutrophils 1-day post challenge with Bacille Calmette-Guerin (BCG) or M. tuberculosis in the lung tissue and in the airspaces of mice, where 1.6% of neutrophils contained mycobacteria [8]. It was demonstrated in human lung tissues that 7% of the cells infected in vitro with various mycobacterial strains consisted of neutrophils [7]. In this paper, we have studied neutrophil cell compartment in patients with active TB disease, analyzing total neutrophils and their subsets in terms of frequencies, phenotype, functional features, and gene expression signature

MATERIALS AND METHODS

DISCUSSION

DATA AVAILABILITY STATEMENT

Findings

ETHICS STATEMENT