DataSheet1_Activation effects on the physical characteristics of T lymphocytes.PDF

The deformability of leukocytes is relevant to a wide array of physiological and pathophysiological behaviors. The goal of this study is to provide a detailed, quantitative characterization of the mechanical properties of T cells and how those properties change with activation. We tested T cells and CD8+ cells isolated from peripheral blood samples of healthy donors either immediately (naïve population) or after 7 days of activation in vitro. Single-cell micropipette aspiration was used to test the mechanical properties. T cells exhibit the general characteristics of a highly viscous liquid drop with a cortical “surface” tension, Tcort. The time course of each cell entry into the micropipette was measured at two different aspiration pressures to test for shear thinning behavior. The data were analyzed in the framework of an approximate mechanical model of the cell deformation to determine the cortical tension, the cell volume, the magnitude of the initial cell entry, the characteristic viscosity μo, and the shear thinning coefficient, b. Activation generally caused increases in cellular resistance to deformation and a broadening of the distribution of cell properties. The cell volume increased substantially upon cell activation from ∼200 μm3 to ∼650 μm3. Naive and activated T cells had similar mean cortical tension (∼150 pN/μm). However, compared to naïve CD8+ cells, the cortical tension of activated CD8+ cells increased significantly to ∼250 pN/μm. Dynamic resistance of naive CD8+ T cells, as reflected in their characteristic viscosity, was ∼870 Pa and significantly increased to 1,180 Pa after in vitro activation. The magnitude of the instantaneous projection length as the cell enters the pipette (Linit) was more than doubled for activated vs. naive cells. All cell types exhibited shear thinning behavior with coefficients b in the range 0.5–0.65. Increased cell size, cortical tension, and characteristic viscosity all point to increased resistance of activated T cells to passage through the microvasculature, likely contributing to cell trapping. The increased initial elastic response of cells after activation was unexpected and could point to instability in the cell that might contribute to spontaneous cell motility.

白细胞的变形能力与众多生理及病理生理行为密切相关。本研究旨在对T细胞的力学特性及其随活化状态的变化进行细致的定量表征。我们对从健康供体外周血样本中分离得到的T细胞与CD8阳性（CD8+）T细胞分别进行了即刻检测（对应初始未活化（naïve）群体），以及经7天体外（in vitro）活化培养后的检测。采用单细胞微管抽吸术（single-cell micropipette aspiration）检测其力学特性。T细胞表现出具有皮层"表面"张力Tcort的高粘性液滴的一般力学特征。我们在两种不同抽吸压力下测量了每个细胞进入微管的时间进程，以验证其剪切变稀行为（shear thinning behavior）。基于细胞变形的近似力学模型框架对数据进行分析，以确定皮层张力、细胞体积、初始细胞进入长度、特征黏度μo以及剪切变稀系数b。细胞活化通常会提升细胞的抗变形能力，并使细胞特性的分布范围变宽。活化后细胞体积显著增加，从约200 μm³增至约650 μm³。初始未活化与活化T细胞的平均皮层张力相近，约为150 pN/μm。然而，与初始未活化CD8+ T细胞相比，活化后的CD8+ T细胞皮层张力显著升高至约250 pN/μm。初始未活化CD8+ T细胞的动态阻力（以特征黏度表征）约为870 Pa，经体外活化后显著升至1180 Pa。活化组细胞进入微管时的瞬时投射长度（Linit）较未活化组增加了一倍以上。所有细胞类型均表现出剪切变稀行为，其系数b处于0.5~0.65区间内。细胞体积增大、皮层张力提升以及特征黏度升高，均表明活化T细胞通过微血管系统的阻力增加，这可能促成了细胞截留现象。活化后细胞初始弹性响应的增强是一项意外发现，其可能暗示细胞内部存在不稳定因素，进而促进自发细胞运动。