Leukocyte biophysics. An invited review

Prior research has shown that leukocytes possess distinct mechanical behaviors that influence their function in immune responses. It was already known that these cells can transition between passive and active states, each with unique structural and mechanical features. However, the precise mechanisms governing these transitions remain unclear. No prior work had resolved the detailed relationship between membrane properties and the cell's ability to deform and move. This gap motivated a deeper investigation into the biophysical characteristics of leukocytes. Understanding these properties could clarify how immune cells navigate through tissues and respond to stimuli. The passive state of leukocytes is characterized by a spherical shape and membrane folds, but the implications for function are not fully understood. This uncertainty drove the need for a comprehensive review of the current knowledge on leukocyte biophysics.

This study aims to review the biophysical properties of leukocytes in both passive and active states. The specific problem addressed is the lack of a unified understanding of how these properties influence immune cell behavior. The motivation for this work stems from the need to clarify the mechanical constraints that affect leukocyte function. By synthesizing existing literature, the authors hope to provide a clearer picture of the mechanical behavior of these cells. The focus is on the relationship between membrane deformability and cellular movement. The study also examines how internal cytoplasmic deformation contributes to leukocyte activity. The goal is to identify the key factors that determine the mechanical response of leukocytes. This review is intended to guide future research on immune cell mechanics.

The authors employed a review approach to analyze the biophysical properties of leukocytes. They examined the structural features of the cell membrane and cytoplasm in both passive and active states. The review included an assessment of viscoelastic properties and membrane deformation under stress. Theoretical models of cytoplasmic motion were also evaluated. The researchers considered the role of membrane area constraints in cellular behavior. They analyzed the effects of membrane tension on large deformations. The study incorporated measurements of strain and strain rate tensors to quantify internal deformation. The authors synthesized findings from multiple experimental techniques to present a comprehensive overview.

The strongest finding from the literature is that passive leukocytes exhibit viscoelastic behavior. The cytoplasm and nucleus bear most of the stress in the unstressed state. Membrane folds allow for high deformability in shearing and bending. However, the membrane resists area expansion, which limits certain cellular functions. Membrane tension becomes significant during large deformations when the membrane unfolds. The constant membrane area constraint affects phagocytic capacity and cell spreading. In the active state, leukocytes undergo internal cytoplasmic deformation and pseudopod projection. Theoretical models suggest that macromolecular reactions drive these mechanical changes.

The authors propose that the biophysical properties of leukocytes are critical for their function. The passive state is characterized by a spherical shape and membrane folds. The cytoplasm and nucleus carry most of the stress in this state. Membrane deformability influences the cell's ability to move and spread. The constant membrane area constraint plays a role in phagocytosis and pore passage. In the active state, internal deformation and granule redistribution occur. Theoretical models link these changes to macromolecular reactions. The authors suggest that further research is needed to clarify the exact mechanisms of cytoplasmic motion.