Microfluidic determination of lymphocyte vascular deformability: effects of intracellular complexity and early immune activation

Despite the critical importance of mechanical (rheological + extrudability) deformability in the vascular flow of lymphocytes, it has been poorly investigated due to the limitations of existing technological tools. Microfluidics analysis of leukocyte deformability offers significant advantages in that it offers high throughput, large sample population and the ability to analyze a heterogeneous population. These advantages are in stark contrast to previous approaches that focused on single cell measurements. Importantly, the flow characteristics of microfluidic devices more closely model vascular deformability in that shear stress is applied forcing leukocyte passage through micropores of designed size. The modeling of vascular flow has been further enhanced by the development of a microfluidic ratchet device that introduced an oscillatory flow. As demonstrated in this study, the microfluidic ratchet device was able to separate human peripheral blood leukocyte subsets (i.e., monocytes and lymphocytes) based on differential deformability profiles. Furthermore, morphologically similar lymphocyte subsets (CD4, CD8 and NK) could also be separated. The subset separation was observed to be largely due to differences in their intracellular complexity (i.e., granule content) with granule-positive T lymphocytes and NK cells being less deformable than granule-negative lymphocytes. Moreover, upon immune activation, deformability of the de-granulated lymphocytes increased consequent to the decrease in cytoplasmic granularity/viscosity. This study for the first time demonstrates that leukocytes subsets have differential deformability profiles and that intracellular granularity/degranulation significantly impacts the lymphocytes' mechanical properties. These findings could be of clinical value as biomarkers of lymphocyte activation state and potential disease processes.