Flexibility of single microvilli on live neutrophils and lymphocytes

We measured the flexural stiffness of single microvilli on live human neutrophils and lymphocytes using 40-nm fluorescent beads. The beads were bound to the tips of the microvilli by anti- L -selectin antibodies. Digital bead images were acquired with an exposure time of 3 s at high magnification. Using a Gaussian point spread function, we obtained an analytical expression that relates the image profile to the flexural stiffness. We found that the flexural stiffnesses were 7 and 4 pN/μm for single microvilli on human neutrophils and lymphocytes, respectively. We also verified with live cells that 75% of neutrophil L -selectin and 72% of lymphocyte L -selectin were on the microvillus tips. Our results indicate that the leukocyte microvilli in contact with the endothelium or other surfaces will bend easily under physiological shear stresses.