Macrophages - The Big Eaters

Macrophages are present in almost all tissues. They are contributing to various processes in the healthy organism, such as development, wound healing, infection and tissue homeostasis. They can rapidly change their phenotype in response to variations in their environment. Macrophages are known for their classical function as antimicrobial phagocytes but support immune function as well by the presentation of antigens. Their research applications are vast, and in vitro assays are increasingly used in a wide range of research areas, including immunology, bacteriology and parasitology, as well as in biomedical and transplantation studies. Two advantages of macrophages in cell culture are that they are relatively easy to generate and to cultivate.

Video 1: Macrophages were imaged for over 24h at a frequency of 1 image every 10 seconds

Marker-free Imaging of Cryopreserved Human M1 Macrophages

In these videos – obtained with Nanolive’s 3D Cell Explorer – we present cryopreserved human M1 macrophages from PromoCell in cell culture (video 1). The 3D Cell Explorer allows to image these living macrophages in a novel, marker-free fashion. A special note goes to the visualization of membrane ruffling as waves arising at the leading edge of lamellipodia that move centripetally toward the main cell body. Macrophages were imaged for over 24h at a frequency of 1 image every 10 seconds.

Phagocytosis Assay Kits by PromoCell were used to test the viability and cellular functioning of the macrophages (video 2 & 3). E.coli particles, visible as small ellipsoid particles, are trapped by the cells, transported and lysed. This system can be used to provide a robust screening system for activators and/or inhibitors of phagocytosis and Toll-like Receptor (TLR) ligands.

Video 2: Macrophages were imaged with Nanolive’s 3D Cell Explorer for over 24h at a frequency of 1 image every 10 seconds. Green circles indicate E.coli being engulfed through phagocytosis

Video 3: Macrophages were imaged with Nanolive’s 3D Cell Explorer for over 4h at a frequency of 1 image every 10 seconds. Green circles indicate E.coli being engulfed through phagocytosis

The Perfect Murder – Macrophage Cell Killed by T-cells

The importance of T-cells and macrophages in our immune system

As part of the human immune system, T-cells are designed to identify HLA (Human leukocyte antigens) display proteins that are not part of the normal cell and therefore indicate the presence of a pathogen inside the cell. T-cells circulate in the bloodstream with proteins on their surface termed T-cell receptors. These receptors scan the HLA display proteins looking for a match. The body is equipped with a vast number of T-cells each displaying only one kind of T-cell receptor with the purpose that the variation in the repertory will allow the identification of many kinds of different pathogens. When a given T-cell receptor does fit well with an HLA display protein it signals the adaptive immune system to spring into action and mount an immune response.

Macrophages are a type of white blood cell of the immune system that engulfs and digests cellular debris, foreign substances, microbes, cancer cells, and anything else that does not seem to be a healthy body cell.

The perfect murder – Macrophage cell killed by T-cells

In this movie, we can observe macrophages and T-cells interacting. Naive T-cells are being presented with antigens by the macrophages which “instruct” T-cells on what type of cells to target (such as cancer cells) and kill. During this interaction, T-cells can play a role in immune system homeostasis (Andersen, 2018) by killing the macrophage presenting the antigen. It was documented that the event is triggered by the presence of specific markers on the macrophage surface (called TRAIL and TWEAK (Kaplan et al., 2018)) telling T-cells to induce apoptosis of their fellow macrophage. The dead macrophage is then seen to be recycled by other macrophages, making space for new macrophages to be produced while keeping the same overall macrophage population.

In this video, pre-stimulated antigen presenting cells (APCs, namely dendritic cells and macrophages, obtained after isolation and in vitro differentiation of bone marrow cells from C57BL/6 mice, pre-stimulation of the APCs has been done with IFN-gamma and LPS) are cultured with freshly isolated “naïve T cells” from the spleen of OT-I mice and observed at a frequency of 1 image every 10 sec for 16 hours.*

*All primary cells were freshly isolated from mice (C57BL/6 background). Naïve t-cells were also obtained from OT-I mice.

Andersen, M. H. (2018). The Balance Players of the Adaptive Immune System, (15), 1–5.

Kaplan, M. J., Ray, D., Mo, R., Raymond, L., Richardson, B. C., & Richardson, B. C. (2018). TRAIL (Apo2 Ligand) and TWEAK (Apo3 Ligand) Mediate CD4 + T Cell Killing of Antigen-Presenting Macrophages.