Spatio-temporal Force Patterns Reveal a Mechanical Set Point in Early T Cell Activation

Abstract

Mechanical forces are increasingly recognized as critical regulators of T cell activation, yet their earliest dynamics remain poorly resolved. Here, we use traction force microscopy on ultra-soft, antigen-presenting-cell-like polyacrylamide substrates to quantify the first 15 minutes of force generation by Jurkat and primary human CD4 T cells under controlled activating conditions. By combining time-resolved stress mapping with spatial tensor analysis, we uncover previously unrecognized heterogeneity in early T cell mechanosensing. Rather than producing a single stereotyped mechanical response, T cells exhibit three distinct temporal force regimes: low-amplitude active fluctuations, intermittent force bursts, and sustained sigmoidal buildups of stress. These temporal programs tightly couple to spatial organization: fluctuating and intermittent behaviors associate with disordered stress distributions, whereas sustained sigmoidal responses predominantly accompany polarized, dipolar, and unexpectedly extensile stress patterns. Substrate stiffness strongly reshapes this distribution, with stiffer gels suppressing sustained high-energy responses and biasing cells toward fragmented mechanical engagement. Primary T cell subsets likewise display distinct force phenotypes: naive cells exhibit weak, fluctuating behaviors, whereas memory cells more readily enter sustained high-force states. Together, these findings support a two-stage model of early T cell mechanosensing in which filopodia-mediated probing generates low, intermittent forces that, upon sustained engagement, transition to a lamellipodia-driven spreading phase producing larger, persistent, and predominantly outward-directed stresses. This framework provides a mechanistic explanation for how substrate mechanics, receptor context, and immune cell state shape force generation during the earliest stages of activation. More broadly, our results identify force as a dynamic and structured component of antigen recognition rather than a passive consequence of T cell signaling. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=130 SRC="FIGDIR/small/480084v4_ufig1.gif" ALT="Figure 1"> View larger version (34K): org.highwire.dtl.DTLVardef@29e24dorg.highwire.dtl.DTLVardef@1c8399forg.highwire.dtl.DTLVardef@3f29edorg.highwire.dtl.DTLVardef@d9a581_HPS_FORMAT_FIGEXP M_FIG C_FIG