The human body is a marvel of evolution, and our blood is no exception. Recent research has revealed that our blood cells may contain an evolutionary relic older than animals themselves, dating back 700 million years. This groundbreaking discovery challenges our understanding of blood's origins and highlights the intricate connections between different life forms. The study, led by Hiroshi Kawamoto of Kyoto University, utilized transcriptome data from various species, including humans, mice, zebrafish, sea squirts, sea urchins, flies, worms, sponges, and unicellular organisms. By analyzing shared patterns in gene expression, the researchers traced the evolutionary history of blood cells, revealing surprising connections to single-celled ancestors.
The findings suggest that the first blood cells were more akin to macrophages, large white blood cells that act as mobile scavengers, engulfing and digesting interloping microbes. Interestingly, some unicellular organisms possess genetic programs similar to those of macrophages, including phagocytosis, the process of engulfing particles. The gene Fos, which regulates cell growth and change, is repeatedly found in both animal blood cells and unicellular organisms, further supporting this connection.
The researchers observed that when they turned up the expression of Fos in a unicellular organism, the cells remained in an isolated, amoeba-like state, rather than clustering together. This suggests that the genetic machinery for macrophage-like behavior emerged in single-celled organisms long before animals and unicellular eukaryotes diverged from a common ancestor.
From these macrophage-like ancestral blood cells, two major evolutionary branches emerged. One branch led to the ancestors of mast cells, which act as the immune system's alarm against intruders. These mast cells later gave rise to T cells, red blood cells, and platelets. The other branch resulted in B cells, which produce antibodies.
The study's implications are far-reaching. It provides insights into the evolution of diseases like cancer and highlights our deep-time heritage. As Yosuke Nagahata, the first author of the study, reflects, the legacy of our distant ancestors circulates within our bodies as blood cells, connecting us to the very roots of life. This research not only deepens our understanding of evolution but also offers a fascinating perspective on the intricate web of life that connects all living beings.
