Modelling Bovine Granuloma Formation In Vitro upon Infection with <i>Mycobacterium Avium</i> Subspecies <i>Paratuberculosis</i>

• Main Authors: J. Hunter Rice, Margaret M. McDaniel, Alyson Holland, Shigetoshi Eda
• Format: Article
• Language: English
• Published: MDPI AG 2019-10-01
• Series: Veterinary Sciences
• Subjects: granuloma; mycobacterium; paratuberculosis; modelling; pathogenesis; johne’s
• Online Access: https://www.mdpi.com/2306-7381/6/4/80

<i>Mycobacterium avium</i> subspecies <i>paratuberculosis</i> (<i>Map</i>) causes chronic granulomatous disease in cattle and ruminant livestock, causing substantial economic losses. Current vaccines delay clinical signs but cannot train the immune system to fully eradicate latent <i>Map</i>. During latency, <i>Map</i> uses host defenses, cage-like macrophage clusters called granuloma, as incubators for months or years. We used an in vitro model to investigate the early coordination of macrophages into granuloma upon <i>Map</i> infection over ten days. We found that at multiplicities of infection (MOI; <i>Map</i>:macrophages) of 1:2 and below, the macrophages readily form clusters and evolve pro-inflammatory cytokines in keeping with a cell-mediated immune response. At higher MOIs, viability of host macrophages is negatively impacted. At 1:4 MOI, we quantified viable <i>Map</i> in our model and confirmed that intracellular <i>Map</i> reproduced over the first five days of infection. Host cells expressed Type 1-specific cytokines, and <i>Map</i>-infected macrophages displayed reduced motility compared to <i>Map</i>-exposed, uninfected macrophages, suggesting an important role for uninfected macrophages in the early aggregative response. Reported is the first in vitro JD granuloma model capturing <i>Map</i> and macrophage viability, size distribution of resulting clusters, motility of monocyte-derived macrophages, and cytokine response during clustering, allowing quantitative analysis of multiple parameters of the <i>Map</i>-specific granulomatous response.