Stiffness fluctuations in T cells.

The actomyosin cortex is a highly dynamic cellular structure that regulates cell shape, migration, and division, while also contributing to specialized functions such as microvillar search. Previous studies have documented fluctuations in microvillar shape and cortical thickness over time. Building on these observations, we investigated whether these morphological changes are accompanied by corresponding fluctuations in cellular stiffness. We used profile microindentation and micropipette aspiration to examine the mechanical properties of human CD4 + T cells. Our results revealed that a substantial proportion of T cells exhibit spontaneous stiffness fluctuations, with approximately one-third displaying clear, periodic peaks with an average period of 30-35 s. Disrupting the actin cytoskeleton with Latrunculin A eliminated these fluctuations, confirming their actin-dependent nature. Low-pressure micropipette aspiration experiments showed periodic movements of cell bodies within the micropipette that correlated with stiffness peaks. These findings demonstrate that the mechanical properties of resting T cells are far from static. Instead, T cells exist in a highly dynamic state characterized by significant stiffness oscillations that may be integral to the microvillar search process. This work raises questions about whether similar mechanical dynamics occur in other cell types and how these periodic stiffness changes might influence T cell immune functions. Our study underscores the importance of temporal resolution when investigating cellular mechanics, as static measurements may miss these fundamental dynamic properties.