Title: Mechanosensing in Naive CD4+ T cells
Description: T cells are key players in adaptive immune response. Originating from the thymus, they seek and eliminate infected cells in various locations of our body. T cells are not anchorage-dependent in nature. However, in our body, cells are constantly under physiological stress. It is not yet known how natural changes in physical environment could affect T cell behaviors. This thesis focuses to study the role, pathway, and main mechanism of rigidity sensing in T cells. Most studies of T cell rigidity sensing have showed that T cell responses are sensitive to external forces. It is unclear whether T cells could generate forces, translate them to biochemical signaling, and regulate their function based on the physical sensing. We tested the idea by developing the use of substrate with varying modulus to analyze the impact of rigidity to T cell activation. We demonstrated that mouse naive CD4+ T cells were capable of sensing and transmitting information from substrate modulus, ultimately affecting the regulation of cytokine secretion, a key indicator of T cell activation.

Interestingly, this cytokine secretion correlated with increasing substrate rigidity. This increased cytokine secretion diminished when T cells lost the ability to contract in sensing the underlying substrate rigidity. Contrary to the presumption that T cells are not able to regulate their function based on the forces applied to the environment, our study provides the first demonstration that substrate rigidity has a functional impact to naive CD4+ T cell activation. To understand the translation process from physical to biochemical signaling in T cells, we determined the signaling pathway that regulated T cell rigidity sensing. We found that T cell rigidity sensing was associated with the signaling molecules of the T cell receptor (TCR) complex, the central pathway of T cell response. Analysis of TCR signaling molecules revealed that T cell rigidity sensing was mediated downstream of the early signaling components in the TCR complex. Lastly, we developed a method of combining micron-scale patterning in elastic substrates to determine whether T cell mechanosensing was mediated from local adhestion sites or globally throughout the cell.

Circular features of primary signal for naive CD4+ T cells were spatially segregated and patterned on elastic substrates to analyze T cell contractility in generating forces across the segregated primary signals, leading to sustained TCR triggering. We found out that T cell contractility failed to generate forces when the primary signals were arranged in equilateral triangle geometry, leading to loss of TCR triggering. This result shows that T cell rigidity sensing is mediated globally throughout the whole cell rather than locally from adhesion sites. Furthermore, the loss of TCR triggering by T cells when sensing the equilateral triangle geometry in elastic substrates opens up new ideas in characterizing force generation within the cell.