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 these videos, 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. https://doi.org/10.1158/0008-5472.CAN-17-3607
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. https://doi.org/10.4049/jimmunol.164.6.2897