Search

Primary infection with Mycobacterium tuberculosis ( Mtb ) results in the formation of a densely packed granulomatous response that essentially limits the entry and efficacy of immune effector cells. Furthermore, the physical nature of the granuloma does not readily permit the entry of therapeutic agents to sites where organisms reside. The Mtb cell wall mycolic acid, trehalose 6,6'-dimycolate (TDM), is a physiologically relevant molecule for modelling macrophage-mediated events during the establishment of the tuberculosis-induced granuloma pathogenesis. At present, there are no treatments for tuberculosis that focus on modulating the host's immune responses. Previous studies showed that lactoferrin (LF), a natural iron-binding protein proven to modulate inflammation, can ameliorate the cohesiveness of granuloma. This led to a series of studies that further examined the effects of recombinant human LF (rHLF) on the histological progression of TDM-induced pathology. Treatment with rHLF demonstrated significant reduction in size and number of inflammatory foci following injections of TDM, together with reduced levels pulmonary pro-inflammatory cytokines TNF-α and IL-1β. LF facilitated greater penetration of fluoroquinolone to the sites of pathology. Mice treated with TDM alone demonstrated exclusion of ofloxacin to regions of inflammatory response, whereas the animals treated with rHLF demonstrated increased penetration to inflammatory foci. Finally, recent findings support the hypothesis that this mycobacterial mycolic acid can specifically recruit M1-like polarized macrophages; rHLF treatment was shown to limit the level of this M1-like phenotypic recruitment, corresponding highly with decreased inflammatory response.

Murine models of Mycobacterium tuberculosis (Mtb) infection demonstrate progression of M1-like (proinflammatory) and M2-like (anti-inflammatory) macrophage morphology following primary granuloma formation. The Mtb cell wall cording factor, trehalose 6,6'-dimycolate (TDM), is a physiologically relevant and useful molecule for modeling early macrophage-mediated events during establishment of the tuberculosis-induced granuloma pathogenesis. Here, it is shown that TDM is a major driver of the early M1-like macrophage response as seen during initiation of the granulomas of primary pathology. Proinflammatory cytokines tumor necrosis factor-α, IL-1β, IL-6, and IL-12p40 are produced in lung tissue after administration of TDM to mice. Furthermore, CD11b + CD45 + macrophages with a high surface expression of the M1-like markers CD38 and CD86 were found present in regions of pathology in lungs of mice at 7 days post-TDM introduction. Conversely, only low phenotypic marker expression of M2-like markers CD206 and EGR-2 were present on macrophages. These findings suggest that TDM plays a role in establishment of the M1-like shift in the microenvironment during primary tuberculosis., (Copyright © 2020 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.)