Reproducible dissociation of cellular aggregates with a wide range of calibrated shear forces: application to cytolytic lymphocyte target cell conjugates.

This paper describes a simple methodology that allows reproducible generation of calibrated shear flows over a wide range (100-fold) of shear rates. This was illustrated by studying the dissociation by shear of alloimmune lymphocyte-target cell conjugates; mixtures of target tumor cells and immune lymphocytes of the same H-2 haplotype were used as controls. Also, current methods of cell agitation (vortexing and aspirating with a Pasteur pipette) were compared with calibrated shearing. Three conclusions are suggested: (i) there is a wide range of resistance of lymphocyte target cell bonds, without any clearcut separation between weak and strong association. Hence any study made on this (and most probably other types of) intercellular adhesion is dependent on the arbitrary definition of 'bound' cells: such a definition should be as absolute as possible, especially when rosetting assays are performed to study different subsets of immunologically competent cells, and when results obtained in different laboratories are compared. (ii) There is no clearcut separation between the strength of specific and nonspecific interactions, there is thus no simple way of using shearing forces to selectively eliminate the latter. (iii) The methods described should help to study the mechanism of immunological processes involving intercellular contacts such as cell-mediated cytotoxicity or antigen-induced lymphocyte activation.