T-cell-fibroblast hybridoma deformability and concanavalin A-induced agglutination

Splitting cell adhesiveness into independent measurable parameters by comparing ten human melanoma cell lines

The concept of cell adhesiveness was analyzed by looking for correlations between the adhesive behavior and measurable biological properties of different cell populations. Ten established lines of melanoma cells were assayed for passive deformability (by micropipet aspiration), active spreading (by measuring the height/diameter ratio after incubation on different surfaces), density and mobility of concanavalin A binding sites (by quantitative analysis of fluorescence microscopic images), spontaneous and concanavalin A-mediated agglutination (by measuring the number of cell conjugates resisting calibrated shearing forces), and binding to glass capillary tubes (with a quantitative assay of binding strength). Forty-four different parameters were thus measured, and each set of determinations was repeated 2 or 3 t at different days on each cell line. Analysis of variance was performed to assess the capacity of each parameter to discriminate between different lines. Correlations between different parameters were studied in order to understand a possible influence of cell intrinsic properties on the behavior of individual cells. The following conclusions were suggested by experimental data 1. Cell spreading ability, resistance to slow deformation within a micropipette and ability to form shear-resistant bonds, are independent properties. It is therefore suggested that different mechanisms rule the cell deformations on time scales of several minutes, tens of seconds, and fractions of a second. 2. Cell spreading ability may effectively influence binding strength only when adhesive stimuli are low, since in this case, cell stiffness is likely to impair the formation of extensive contact areas. 3. Individual cells may display marked heterogeneity within a given population, that emphasizes the danger of using averaged parameters to predict rare events (such as metastasis formation). 4. The most useful parameters to discriminate between different cell lines were, spreading ability and shear-resistant lectin agglutination, and substrate adhesion. It is concluded that cell adhesion is influenced by several measurable cellular properties that may display independent variations. The importance of a given parameter depends on the conditions of bond formation and rupture.

Dynamics of complex formation between thymocytes and thymic medullary epithelial cells

Direct cell contact is an intrinsic part of several differentiation processes. A case in point is the formation of complexes between thymic lymphocytes and stromal cells, which are essential for T-cell maturation. The objective of the present work was to gain an insight into the mechanisms underlying the formation and dissociation of such lymphostromal complexes. Using an in vitro system, we show that the number of thymocytes adhering to a thymic medullary epithelial cell line (E-5) increases with time and reaches a plateau, after which some thymocytes spontaneously detach, while the rest remain attached to epithelium. The detached and forcibly removed thymocytes were analysed for their expression of L3T4 and Ly-2 antigens. The detached thymocytes showed a markedly lowered expression of both antigens. Both of these subtypes were shown to be totally refractory to form further complexes after a first encounter with E-5 cells. We also show that, once a mean adherence level of one thymocyte per E-5 cell was reached, (a) the level of further adherence increased exponentially, and (b) during this phase, binding of thymocytes to E-5 cells occurred in clusters, indicating pre-existing polarity or contact-induced polarization of the receptors at the E-5 cell surface.

Quantification of cell surface roughness; a method for studying cell mechanical and adhesive properties

The presence on the surface of nucleated cells of a variety of asperities of different size and shape plays a prominent role in cell-cell and cell-substrate interaction. Also, the organization of these asperities is directly related to cellular cytoskeletal elements. In the present report, we describe a simple and objective method of studying electron micrographs to quantify the roughness of cell contours. Constant-length segments of cell boundaries are compared to reference circular segments with common extremities and enclosing the same area. This procedure was performed with a digitizer connected to a microcomputer, and it was used to analyse model contours or electron micrographs of (i) target tumour cells bound by cytotoxic T lymphocytes and (ii) thymocytes sticking to concanavalin A-coated surfaces. It is shown that this method allows precise quantification of cell deformation in adhesive zones, which may allow absolute evaluation of adhesive stimuli.