Spatio-temporal dynamics of immune cells

Our team is interested in the dynamics of migration and function of immune cells in tissues. We work at the interface of cell biology, immunology and biophysics. We aim at deciphering the fundamental molecular and cell biological mechanisms that enables immune cells to efficiently fulfil their functions.

Twitter: @LennonLab

We work at the interface of cell biology, immunology and biophysics. We aim at deciphering the fundamental cell biological mechanisms that control the spatio-temporal regulation of antigen presentation.

In this context, we develop two main axis of research:

1. the coordination between cell migration and antigen uptake and presentation in dendritic cells

2. the role of cell polarity in immune synapse formation and antigen presentation in B lymphocytes. Our ultimate goals are to unravel the molecular basis accounting for the behavior of antigen presenting cells in tissues and to understand how it impacts immune responses in vivo.

The coordination between cell migration and antigen uptake and presentation in dendritic cells

We found that dendritic cell locomotion and antigen uptake involve common regulatory molecules. This led to the description of the first cell biological mechanism that allows the coordination between cell migration and cell function. This unexpected discovery opened a new research line in our lab whose main goal is to decipher the molecular mechanisms and physical principles that govern dendritic cell migration and to understand how they are linked to their function as immune sentinels. We highlight the central role of the actin-based molecular motor Myosin II in coordinating dendritic cell migration and antigen macropinocytosis by imposing on immature dendritic cells an intermittent migration mode that favors environment patrolling. We further show the key role of the endoplasmic reticulum calcium channel IP3 Receptor 1 in the regulation of Myosin II activity and localization in migrating dendritic cells. We are currently combining microfabricated and biophysical tools with live imaging to understand how Myosin II and various players of the actin cytoskeleton couple antigen uptake to cell migration ex vivo as well as in tissues such as the skin and the gut. We are further investigating how the biochemical and physical extracellular cues of these tissues impact on the molecular mechanisms responsible for the coordination between dendritic cell migration and function. Whether and how such mechanisms and cues have a role in tumor cell migration is also being explored. Identifying the mechanisms that control dendritic cell migration will help using these cells as vaccines in cancer immunotherapy.

Figure 1: A dendritic cell fixed during migration in a micro-channel and stained for actin (blue), Myosin II (green) and CD74 (red). Macropinosomes (giant vesicles used to uptake antigens) are highlighted in the rectangle at the cell front.

The role of cell polarity in immune synapse formation and antigen presentation in B lymphocytes

We have highlighted the membrane trafficking events and associated molecular mechanisms involved in antigen extraction and processing at the B cell synapse. We found that MHCII-containing lysosomes are recruited at the synapse where they locally undergo exocytosis, allowing synapse acidification and the extracellular release of hydrolases that promote the extraction of the immobilized antigen. Lysosome recruitment and secretion results from the CDC42-dependent polarization of the microtubule-organizing center (MTOC). Regulation of B lymphocyte polarity therefore emerges as a central mechanism that couples antigen extraction to antigen processing and presentation. In addition, we have identified the Par3 subunit of the ancestral polarity complex as essential for MTOC and lysosome polarization. Interestingly, we further showed that Par3 is recruited to the B cell immune synapse where it interacts with the microtubule-based molecular motor Dynein to allow centripetal transport of BCR micro-clusters for proper signaling. We are currently using a multidisciplinary approach that combines proteomics, siRNA-based screening and live imaging to identify the molecular mechanisms involved in B cell polarization. A specific focus is given to the proteins that regulate the interface between the actin and microtubule cytoskeleton -including molecular motors- and membrane trafficking. Furthermore, we are investigating how local extracellular cues regulate B lymphocyte polarity and B cell responses in vivo. The molecules identified might represent valuable targets to modulate B cell responses in pathological contexts.