Neutrophil-mediated innate immune resistance to mycobacteria

Abstract

Neutrophils contain antimicrobial peptides with antituberculous activity, but their contribution to immune resistance to tuberculosis (TB) infection has not been previously investigated to our knowledge. We determined differential white cell counts in peripheral blood of 189 adults who had come into contact with patients diagnosed with active TB in London, United Kingdom, and evaluated them for evidence of TB infection and capacity to restrict mycobacterial growth in whole-blood assays. Risk of TB infection was inversely and independently associated with peripheral blood neutrophil count in contacts of patients diagnosed with pulmonary TB. The ability of whole blood to restrict growth of Mycobacterium bovis bacille Calmette Guérin and Mycobacterium tuberculosis was impaired 7.3-and 3.1-fold, respectively, by neutrophil depletion. In microbiological media, human neutrophil peptides (HNPs) 1-3 killed M. tuberculosis. The neutrophil peptides cathelicidin LL-37 and lipocalin 2 restricted growth of the organism, the latter in an iron-dependent manner. Black African participants had lower neutrophil counts and lower circulating concentrations of HNP1-3 and lipocalin 2 than south Asian and white participants. Neutrophils contribute substantially to innate resistance to TB infection, an activity associated with their antimicrobial peptides. Elucidation of the regulation of neutrophil antimicrobial peptides could facilitate prevention and treatment of TB. IntroductionTuberculosis (TB) is a leading global cause of morbidity and death (1). Primary TB infection is acquired by the inhalation of droplets containing Mycobacterium tuberculosis (MTB) bacilli. If innate immunity is insufficient to eliminate infection, the acquired T cell response results in containment of infection in the majority of cases. The immune sensitization that arises can be detected by the delayed-type hypersensitivity reaction to MTB antigens in the form of the tuberculin skin test (TST).It has long been recognized that some individuals exposed to infectious TB resist developing positive TST for longer periods than their peers despite similar exposure levels (2), raising the possibility that the innate immune response can clear infection without induction of an acquired response. Until recently, investigation of factors associated with innate resistance to MTB infection was hampered by the poor sensitivity and specificity of the TST (3). The development of more sensitive and specific blood-based methods to evaluate the T cell response to TB (known as IFN-γ release assays [IFNGRAs]) is therefore an important advance. One such test, the ELISPOT, has recently been used to determine factors associated with resistance to MTB infection in children (4).

Combination of host susceptibility and Mycobacterium tuberculosis virulence define gene expression profile in the host

“…Although the role of neutrophils in protection and pathogenesis in TB remains controversial, these effector cells clearly contribute to inflammation in acute TB [95,96]. The involvement of neutrophil-mediated lung injury could participate in the formation of necrotic and caseous granulomas [97].…”

Galleria mellonella - a novel infection model for the Mycobacterium tuberculosis complex

“…This organism has been very well-characterized and utilized in a wide range of clinical and non-clinical studies [21,24,27–32,51]. For example, differences in M. bovis BCG lux RLU measurements have been shown to reflect changes in the immune response in human whole blood and cellular models, including differences between tuberculin-positive and -negative individuals [23], changes induced by HIV infection and following antiretroviral treatment [25,26], changes in mycobacterial growth limitation induced by vaccines [24] and Vitamin D supplementation in vitro and in a clinical trial [29–31], and differences in gene expression in immune biological pathways compared to M. tuberculosis [32]. In addition we have also evaluated luminescent mycobacteria in the mouse model [27].…”

1α,25‐dihydroxyvitamin D3 inhibits matrix metalloproteinases induced by Mycobacterium tuberculosis infection

“…32 We and others have also previously demonstrated that 1a,25(OH) 2 D 3 induces the antimicrobial peptide cathelicidin LL-37, which possesses antituberculous activity. 22,33,34 PBMC + EtOH This report describes a complementary mechanism whereby vitamin D could exert a beneficial effect on host response to M. tuberculosis by inhibiting the expression, secretion and activity of a number of MMP induced by M. tuberculosis, consequently limiting the degradation of extracellular matrix and decreasing pulmonary cavitation to preserve lung function and reduce infectiousness.…”