Tenacious macrophages
Alveolar macrophages transplanted into mice after prolonged cultivation restore their characteristics
Vera Sysoeva, PCR.news
Resident (tissue) macrophages can be found in all tissues of the body; they perform a variety of functions related to maintaining homeostasis, immune response and self-renewal of the body. In various organs, macrophages form populations that differ phenotypically from each other. It is known that transplantation of macrophages from other tissues into the lungs changes their phenotype, and when cultured ex vivo, alveolar macrophages lose the expression of tissue-specific genes. This is probably due to the loss of environmental signals. It remains unknown whether these changes are reversible and whether macrophages retain sensitivity to specific environmental signals after prolonged cultivation. The answers to these questions were received by researchers from France and Germany.
Currently, macrophages are mainly obtained by differentiation from progenitor cells, while heterogeneous cell populations are formed that can be used for a short period of time. The authors grew mouse macrophages obtained by bronchoscopy ex vivo in an environment containing colony-stimulating factors for granulocytes and macrophages. They managed to cultivate the cells for ten months. In addition, these macrophages withstood several cycles of freezing and defrosting.
The scientists then tested the phenotypic characteristics and functions of the cultured macrophages. They demonstrated the characteristic features of these cells, for example, the ability to phagocytosis and the formation of acidified lysosomes. In addition, the simulation of infection — the addition of Escherichia coli lipidosaccharides to the culture — led to increased production of reactive oxygen species.
RNA sequencing showed that some key genes specific to alveolar macrophages were expressed both in freshly isolated cells and in cultured ones. However, the expression profile of specific genes did change in response to changing environmental conditions. For example, cultivation affected genes associated with lipid metabolism, adhesion, and autocrine signaling for population self-renewal.
Then the scientists checked whether the alveolar macrophages restore their characteristic features when transplanted back into the mouse lungs. They found that after long-term cultivation (two months), alveolar macrophages are able to stably populate animal tissues for at least four months, accounting for 5-15% of all macrophages. At the same time, the expression of those genes that distinguish them from other populations of resident macrophages was fully restored after transplantation into mouse lungs. This means that the adaptation of cells to the conditions of long-term cultivation is reversible. This conclusion was also confirmed by the analysis of chromatin availability: most of the sites returned to their original state after transplantation.
Finally, the transplantation of such macrophages to mice with Csf2rb gene knockout, which lack their own alveolar macrophages, proved to be extremely effective: after eight months, there were almost as many macrophages in the lungs of mice as in wild-type mice. In addition, microscopic examination showed that the amount of mucus and cellular residues accumulated due to the absence of macrophages in the alveolar fluid in these animals also decreased.
Thus, the authors demonstrated that epigenetic changes in the culture of alveolar macrophages are reversible after transplantation back into the body. Other signs of cell adaptation to cultivation, such as changes in cell adhesion, migration, and metabolic features, are also reversible. The authors believe that the cultivation of macrophages will create a new approach to cell therapy: unlike T-cell therapy, which is more suitable for the treatment of blood cancers, macrophages could help in the treatment of solid tumors.
Article by Subramanian et al. Long-term culture-expanded alveolar macrophages restore their full epigenetic identity after transfer in vivo published in the journal Nature Immunology.
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