Neutrophils in Mycobacterium tuberculosis

Abstract

Mycobacterium tuberculosis (M. tb) continues to be a leading cause of mortality within developing countries. The BCG vaccine to promote immunity against M. tb is widely used in developing countries and only in specific circumstances within the United States. However, current the literature reports equivocal data on the efficacy of the BCG vaccine. Critical within their role in the innate immune response, neutrophils serve as one of the first responders to infectious pathogens such as M. tb. Neutrophils promote effective clearance of M. tb through processes such as phagocytosis and the secretion of destructive granules. During the adaptative immune response, neutrophils modulate communication with lymphocytes to promote a strong pro-inflammatory response and to mediate the containment M. tb through the production of granulomas. In this review, we aim to highlight and summarize the role of neutrophils during an M. tb infection. Furthermore, the authors emphasize the need for more studies to be conducted on effective vaccination against M. tb.

Keywords: Mycobacterium tuberculosis; immune system; infection; neutrophils; tuberculosis.

Figure 1

Neutrophil-mediated roles during an immune response. Arginase 1 (ARG-1), major histocompatibility complex II (MHC-II), B-cell activating factor (BAFF), A Proliferation-Inducing TNF Ligabd (APRIL).

Figure 2

Neutrophil response during an active and latent M. tb. infection. During an (A) active infection, alveolar macrophages encounter, and phagocytose M. tb. This results in chemokine release and initiation of margination, rolling, adhesion, and extravasation of neutrophils to the infected site. If the macrophages are unable to eliminate the pathogen themselves, neutrophils may phagocytose the dying, infected macrophages. (B) LTBI commonly occurs via granuloma formation, where the immune system works to contain M. tb. Hypoxic conditions within granulomas have been shown to increase the secretion of enzymes matrix metalloproteinase 8 and 9 (MMP-8, MMP-9), elastase, collagenase, and proteases as well as increase neutrophil life span and reactive nitrogen species. Unregulated neutrophil inflammation contributes to increased bacterial burden and severity of TB infection.