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Updated: Jun 25, 2025
Quantification of Intracellular Growth Inside Macrophages is a Fast and Reliable Method for Assessing the Virulence of Leishmania Parasites
Published on: March 16, 2018
Circadian Regulation of Leishmania Parasite Internalisation in Macrophages and Downstream Cellular Events
Priscilla Carvalho Cabral1, Sophia K Stegeman1, Martin Olivier2
1Douglas Research Centre, McGill University, Montreal, Quebec, Canada.
Abstract:
Leishmania spp. parasites use macrophages as a host cell during infection. As a result, macrophages have a dual role: clearing the parasite as well as acting as host cells. Recently, studies have shown that macrophages harbour circadian clocks, which affect many of their functions such as phagocytosis, receptor expression and cytokine release. Interestingly, Leishmania major infection in hosts was also shown to be under circadian control. Therefore, we decided to investigate what underlies the rhythms of L. major infection within macrophages. Using a culture model of infection of bone marrow-derived macrophages with L. major promastigotes, we show that the parasites are internalised into macrophages with a 24-h variation dependent on a functional circadian clock in the cells. This was associated with a variation in the number of parasites per macrophage. The cell surface expression of parasite receptors was not controlled by the cells' circadian clock. In contrast, the expression of the components of the endocytic pathway, EEA1 and LC3b, varied according to the time of infection. This was paralleled by variations in parasite-induced ROS production as well as cytokine tumour necrosis factor α. In summary, we have uncovered a time-dependent regulation of the internalisation of L. major promastigotes in macrophages, controlled by the circadian clock in these cells, as well as subsequent cellular events in the endocytic pathway, intracellular signalling and cytokine production.
Insights
The timing of Leishmania major parasite entry into macrophages is controlled by the macrophage
Area of Science:
- Immunology
- Chronobiology
- Parasitology
Background:
- Macrophages play a dual role in Leishmania spp. infections, acting as both host cells and parasite-clearing agents.
- Macrophages possess intrinsic circadian clocks that regulate key functions, including phagocytosis and cytokine release.
- Leishmania major infection dynamics in vivo exhibit circadian control, suggesting a rhythmic interaction between parasite and host.
Purpose of the Study:
- To investigate the underlying mechanisms of circadian rhythms in Leishmania major infection within macrophages.
- To determine if the circadian clock of macrophages influences parasite internalization and intracellular fate.
Main Methods:
- Utilized a bone marrow-derived macrophage culture model infected with Leishmania major promastigotes.
- Assessed 24-hour variations in parasite internalization, parasite load per macrophage, and expression of endocytic pathway components (EEA1, LC3b).
- Measured parasite-induced reactive oxygen species (ROS) production and tumor necrosis factor-alpha (TNF-α) cytokine levels.
Main Results:
- Parasite internalization into macrophages demonstrated a 24-hour rhythm, dependent on the macrophage's functional circadian clock.
- The number of parasites per macrophage varied rhythmically.
- Circadian regulation was observed in the expression of endocytic pathway components, ROS production, and TNF-α secretion, but not in parasite receptor expression on the cell surface.
Conclusions:
- Uncovered a time-dependent regulation of Leishmania major promastigote internalization by the macrophage circadian clock.
- Demonstrated circadian control over subsequent intracellular events, including endocytic pathway dynamics, signaling, and cytokine production.
- Highlights the significant role of host cell circadian rhythms in shaping the outcome of Leishmania infection.
