A new study has discovered that human white blood cells use a “molecular paddle” mechanism to swim through a liquid environment. The study found that this mechanism is used for everything from immune repair, which is beneficial to the body, to the spread of cancer cells, which amplifies the damage.
One of the researchers, Olivier Theodoly of the Aix-Marseille Université in France, said, “The ability of cells to move autonomously is a key part of understanding many biological functions, of which we have only partially understood so far. The information found in this study is an important element of immunology and cancer research.”
There are many different mechanisms by which cells move. Sperm, microscopic algae and some bacteria, for example, use an additional site in the form of a flagellum to move within their respective environments. Other somatic cells attach themselves to other contact surfaces and “crawl” by changing the shape of the cell. Scientists have long thought that leukocytes are the latter type and cannot move without attaching to a contact surface.
A previous study found that a type of white blood cell, called neutrophil, has the ability to move forward on its own, but did not understand the exact mechanism. This new study adds to that knowledge by identifying a new mechanism for swimming – the ability to move through a liquid environment without either attaching to a contact surface or changing the shape of the cell. The researchers call this the “molecular paddle” mechanism.
From microscopic 3-D images, it appeared that the cells swam in a breaststroke-like position by changing their shape, but a closer look revealed that this was not the case, and that the seemingly cosmetic changes were not enough to create forward momentum, Theodorie said.
The researchers found that these cells use actin, which is present in the cell membrane and within the protruding tissue outside the cell, to allow the cell’s outer membrane to create a conveyor belt-like movement mechanism that propels the cell forward within a solid or liquid environment, whether or not it is attached to a contact surface.
However, the situation is not yet so simple; the study found that the outer membrane of the cell does not move in a consistent manner like a conveyor belt as a whole; only actin produces this movement, while other types of proteins freely distributed on the cell membrane act as a certain obstacle to the cell’s movement.
The researchers estimate that the entire mechanism is accomplished by a combination of internal and external mechanisms driven by actin. Specifically, on the outside, actin facilitates a conveyor belt-like movement of the outer cell membrane, while inside the cell, near the tail end, some actin is encapsulated in a vesicular structure that continuously circulates from the tail end to the front of the cell, providing sufficient forward momentum to match the movement of the outer membrane.
During this process, other cell membrane proteins are constantly separated from the actin and do not participate in the transport from the tail to the front.
Theodorie said, “The filtering and transport mechanisms of these proteins play a complex role in the cell’s swimming process. Our study unexpectedly links two fields that were almost unrelated – the physics of microscopic swimming and the transport mechanisms of biological vesicles.”
This study was recently published in the Biophysical Journal.
Recent Comments