New chamber for flow cytometric analysis over an extended range of stream velocity and application to cell adhesion measurements

When analyzed in a flow cytometer, particles are suddenly accelerated to high velocities (1–10 m.s −1 ) over very short distances. This feature is essential to obtain high analysis rates and low coincidence levels, but translates into very strong velocity gradients (> 10 5 s −1 ): particles experience strong hydrodynamic stresses that elongate them acid tend to dissociate weakly associated complexes. In order to analyze fragile conjugates formed by heterotypic adhesion between two cell types, a flow cytometer was modified to make hydrodynamic stress not only much weaker but also adjustable. A new and easily adaptable flow cell was designed for the instruments of the FACS™ series; it provided satisfactory hydrodynamic conditions on a wide continous range of flow rates. Accompanying electronic adaptations permitted standard analysis between 0.01 and 10 m.s −1 . At 0.01 m.s −1 , the velocity gradient roughly amounts to 50 s −1 . Conjugates formed by the adhesion between human B and resting T lymphocytes, disrupted in conventional flow cytometers, could be detected and precisely quantified provided analysis velocity was kept below 0.1 m.s −1 . We conclude that low velocity flow cytometry makes possible the quantification of weak intercellular adhesion phenomena, and is potentially useful for the future development of new biomechamical techniques and other applications.