The effects of mechanical forces on lymphocyte adhesion and migration
Bergman, Arthur James
Doctor of Philosophy
The immune system, and in particular, lymphocyte function is depressed under microgravity conditions. Cells may sense altered gravitational forces through changes in the mechanical forces they experience. To study the effects of microgravity on lymphocytes using ground-based methods, we examined the effects of mechanical forces on cellular function. To assay lymphocyte function, adhesion and migration experiments were preformed on extracellular matrix-coated surfaces. A cell migration assay was developed where cells were tracked on a two-dimensional surface. Cell trajectories were reconstructed and analyzed using the persistent random walk model. A simulation was developed to obtain idealized cell trajectories with defined persistent random walk parameters. This simulation was used to verify that our method of analyzing cell trajectory data yielded a reasonable fit of the model. Lymphocytes may sense altered mechanical forces through altered cell-substrate contacts. To investigate this possibility, we studied lymphocyte adhesion and migration on surfaces with different surface chemistry (untreated or tissue culture polystyrene) and with different concentrations of adsorbed fibronectin. Our results showed that cell speed and the effective diffusion of lymphocytes were modulated by altering cell-substrate contacts. To investigate the effects of shear mechanical forces on lymphocyte adhesion and migration, we cultured lymphocytes in a rotating wall vessel (RWV). In this culture system, cells experience a low shear force over an extended period of time (up to 10 days for our experiments). The cells were then removed from culture and their adhesion and migration behavior on extracellular matrix-coated surfaces was determined. Cells cultured in the RWV for four or more days exhibited significantly higher cell speeds but lower persistence times than cells cultured statically. Further, no significant differences in cell adhesion were observed between RWV and statically cultured cells. Our experiments suggest that these differences in migratory behavior between RWV and statically cultured cells were not caused by differences in integrin expression, membrane fluidity or cell cycle regulation. Lastly, we examined the effects of protein kinase C and protein tyrosine kinase on lymphocyte adhesion and migration.
Cell biology; Biomedical engineering; Chemical engineering