The Nanoscale Organisation of Human Macrophage Surfaces Studied by Super-resolution Microscopy

Abstract

Recent advances in super-resolution microscopy revealed that the function of receptor molecules is influenced by their nanoscale organisation within the membrane. This especially applies to macrophages who are one of the most plastic cell types known with a large repertoire of surface receptors tightly regulating their many different functions. In addition, macrophage phenotype is highly influenced by the tissue of residence. However, very little studies have imaged tissue-derived macrophages due to their high autofluorescence. To address this, a novel background correction technique was developed to correct for autofluorescence in stochastic optical reconstruction microscopy (STORM) data sets. Here, a moving median filter was applied prior to image reconstruction to subtract unwanted backgrounds. Importantly, this enabled the investigation of the membrane of human lung macrophages on a nanometer-scale for the first time. Macrophages were activated through their Fc receptors by IgG-coated surfaces, representing a 2D model of the phagocytic synapse. Interestingly, upon activation, lung macrophages formed MHC class I–tipped protrusions. This is consistent with a role of macrophage protrusions in antigen presentation. In addition, macrophages secreted extracellular vesicles (EV) upon activation with IgG. Here, lung- and monocyte-derived macrophages (MDM) were stained for the tetraspanin and EV marker CD81. Crucially, EV were captured directly upon secretion, on a nanometer-scale, enabling the accurate detection of EV diameters and the analysis on a cell-by-cell basis which is not possible, when studying EV as often done in bulk after isolation. The comparison of M0-like, M1-like, M2-like and lung macrophages revealed distinct vesicle characteristics, suggesting distinct functions and mechanisms of biogenesis. Crucially, the number of vesicles secreted differed greatly between single cells, highlighting the heterogeneity of cellular secretions. Proteomics analysis of MDM-derived EV confirmed discrete contents of EV with MHC class I and leukocyte immunoglobulin-like receptor B1 (LILRB1) being enriched in vesicles derived from M2-like and M0-like macrophages, while MHC class I was enriched in M1-like macrophage vesicles. Interestingly, two colour STORM of the LILRB1 and MHC class I showed their co-localisation on M0-like macrophage vesicles.

Date of Award	31 Dec 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Daniel Davis (Supervisor) & Tracy Hussell (Supervisor)