EFFECTS OF SHEAR STRESSES ON HUMAN LYMPHOCYTE FUNCTIONS
CHITTUR, KRISHNAN KALYANARAMAN
Doctor of Philosophy
A modified Couette Viscometer was used to study the effect of shear stresses on human lymphocyte function, the cells that constitute the afferent and efferent paths of the immune response. The lymphocytes were obtained as a heterogenous population of mononuclear cells from the peripheral blood of humans. Shear stress levels investigated in this work were similar in magnitude to those found in blood contacting devices like the blood pumps and hemodialysis units. In these devices high mass transfer rates are achieved at flow rates that expose blood's cellular elements to shear stresses that are much higher than those found physiologically. The functional analysis of shear stressed lymphocytes were achieved by studying proliferative responses to phytohemagglutinin-P(PHA-P), ability to synthesize and release the T cell growth factor, interleukin-2(IL-2), the effects on cell viability, cellular enlargement and cell-cell interactions in the culture sytems. The exposure of the cells to shear stress levels of 100 and 200 dynes/cm('2) for 10 minutes damaged a portion of the mononuclear cell population. Shear stressed cells when cultured at 1 x 10('6) cells/ml did not incorporate significant amounts of thymidine into their DNA nor synthesize detectable levels of IL-2. They also did not exhibit the characteristics cellular enlargement induced by PHA. In contrast however when the shear stressed cells were cultured at decreased cell densities of 0.5 x 10('6) and 0.25 x 10('6) cells/ml they incorporated significantly greater amounts of thymidine along with a concomitant increase in synthesis of IL-2. Increasing the cell to cell contacts in culture resulted in a greater inhibition of the proliferative response. The data suggest that a fraction of cells were shear stress damaged and that such damage inhibited the proliferation of the other cells in a density dependent manner. Analysis of the relative membrane potentials of lymphocytes after shear stress exposure showed that shear stress interfered with the depolarizing action of PHA. These results suggested that the action of shear stresses on lymphocyte function could be explained in terms of events at the cells' plasma membrane.