White blood cells can swim, upending previous research, French scientists discover

Lymphocytes, white blood cells crucial to the body's immune system, can swim, according to new research by a team of researchers from various French universities.

Led by scientists at the Aix-Marseille University in southern France, the researchers have upended previous theories that blood cell mobility depends on friction.

"Interactions with the substrate by adhesion or friction are widely accepted as a prerequisite for mammalian cell motility, which precludes swimming," the paper notes.

It now appears the cells are less passive and move in what appears, in two dimensions, to be a type of breast stroke, according to the research published in the Biophysical Journal.

However, it is not believed that these breast stroke deformations propel the cells forward.

“Looking at cell motion gives the illusion that cells deform their body like a swimmer,” noted co-senior study investigator Chaouqi Misbah, Ph.D., professor at Grenoble Alpes University told Genetic Engineering and Biotechnology News. “Although leukocytes display highly dynamic shapes and seem to swim with a breaststroke mode, our quantitative analysis suggests that these movements are inefficient to propel cells.”

Instead the researchers discovered proteins spanning the membrane act like tiny oars to propel the cells forward.

"We show here experimental and computational evidence that leukocytes do swim, and that efficient propulsion is not fueled by waves of cell deformation but by a rearward and inhomogeneous treadmilling of the cell's external membrane," the paper states.

“The capacity of living cells to move autonomously is fascinating and crucial for many biological functions, but mechanisms of cell migration remain partially understood,” said co-senior study investigator Olivier Theodoly, Ph. D, head of the adhesion and inflammation lab at Aix-Marseille University, told Genetic Engineering and Biotechnology News (GEN). “Our findings shed new light on the migration mechanisms of amoeboid cells, which is a crucial topic in immunology and cancer research.”

Theodoly added: "This recycling of the cell membrane is studied intensively by the community working on intracellular vesicular traffic, but its role in motility was hardly considered. These functions of protein sorting and trafficking seemed highly sophisticated for swimming. Our investigations, to our surprise, bridge such distant domains as the physics of microswimmers and the biology of vesicular traffic.”

According to the research, the model "consists of a molecular paddling by transmembrane proteins linked to and advected by the actin cortex, whereas freely diffusing transmembrane proteins hinder swimming."

The researchers add: "furthermore, continuous paddling is enabled by a combination of external treadmilling and selective recycling by internal vesicular transport of cortex-bound transmembrane proteins. This mechanism explains observations that swimming is five times slower than the retrograde flow of cortex and also that lymphocytes are motile in nonadherent confined environments."