No abstract

A direct measurement of the avidity of the junction between a cytotoxic T lymphocyte and its target cell was achieved by using a biophysical approach. A micromanipulation technique was used to determine the force required to separate a cytotoxic T cell (human clone F1, with specificity for HLA-DRw6) from its specific target cell (JY: HLA-A2, -B7, -DR4, w6) prior to delivery of the lethal hit. The force required to separate the F1-JY pair is 1.5 X 10(4) dynes per square centimeter. This junction avidity for F1-JY pairs is 6 to 13 times greater than that for F1-F1 and JY-JY pairs; the F1-JY conjugate requires a stronger separating force and is more easily rejoined than the homologous cell pairs. This study provides an estimate of the avidity of cytotoxic T cells for their target cells and insights into the biophysical correlates of the molecular complexes formed in the interaction of cytotoxic T cells and their targets during the cytotoxic process.

The rheological properties of human leukocytes (WBCs) have been studied by micropipette aspiration and filtration tests. A small aspiration pressure applied via a micropipette (diameter approximately equal to 3 micron) causes the WBC to undergo a rapid elastic deformation followed by a slow creep. The data can be analyzed with a viscoelastic model: an elastic element K1 in parallel with a Maxwell element (elastic element K2 in series with viscous element mu). Neutrophils and B lymphocytes are similar in K1, K2, and mu, but these values are higher for T lymphocytes. Treatment of neutrophils with colchicine decreases K2 and mu without changing K1, whereas cytochalasin B decreases all three coefficients; these results indicate the importance of cytoskeletal microtubules and microfilaments in WBC rheology. In the presence of Ca2+, WBCs form protopods which have increased viscoelastic coefficients. Inhibition of protopod formation with pentoxifylline is associated with an increase in WBC deformability. The ruffled surface of the apparently round WBC provides an area about twice that needed to enclose a smooth sphere of the same volume; this geometric feature plays an important role in whole WBC deformability tested through 4-5 micron filter pores or micropipettes. Because of its larger volume and higher cellular viscosity, each WBC is equivalent to approximately 700 erythrocytes in its tendency to block 5-micron channels. The rheology of WBCs has significant implications in their functional behavior, including flow through the microcirculation and interaction with endothelial cells.

Tendons and ligaments exhibit limited regenerative capacity following injury, with damaged tissue being replaced by a fibrotic scar. The physiological role of scar tissue is complex and has been studied extensively. In this study, we demonstrate that rat tendons contain a unique subpopulation of cells exhibiting stem cell characteristics, including clonogenicity, multipotency, and self-renewal capacity. Additionally, these putative stem cells expressed markers consistent with neural crest stem cells (NCSCs). Using immunofluorescent labeling, we identified P75 + (p75 neurotrophin receptor) cells in the perivascular regions of the native rat tendon. Importantly, P75+ cells were frequently localized near vascular cells and increased in number within the peritenon after injury. Ultrastructural analysis showed that perivascular cells detached from vessels in response to injury, migrated into the interstitial space, and deposited extracellular matrix. Characterization of P75 + cells isolated from the scar tissue indicated that this population also expressed the NCSC markers, Vimentin, Sox10, and Snail. In conclusion, our results suggest that neural crest-like stem cells of perivascular origin reside within the rat peritenon and give rise to scar-forming stromal cells following tendon injury.