Temporal dynamics in an immunological synapse: Role of thermal fluctuations in signaling.

ABSTRACT

The article analyzes the contribution of stochastic thermal fluctuations in the attachment times of the immature T-cell receptor TCR peptide-major-histocompatibility-complex pMHC immunological synapse bond. The key question addressed here is the following how does a synapse bond remain stabilized in the presence of high-frequency thermal noise that potentially equates to a strong detaching force? Focusing on the average time persistence of an immature synapse, we show that the high-frequency nodes accompanying large fluctuations are counterbalanced by low-frequency nodes that evolve over longer time periods, eventually leading to signaling of the immunological synapse bond primarily decided by nodes of the latter type. Our analysis shows that such a counterintuitive behavior could be easily explained from the fact that the survival probability distribution is governed by two distinct phases, corresponding to two separate time exponents, for the two different time regimes. The relatively shorter timescales correspond to the cohesionadhesion induced immature bond formation whereas the larger time reciprocates the associationdissociation regime leading to TCRpMHC signaling. From an estimate of the bond survival probability, we show that, at shorter timescales, this probability P(Δ)(τ) scales with time τ as a universal function of a rescaled noise amplitude D/Δ(2), such that P(Δ)(τ)∼τ(-(Δ/√[D]+1/2)),Δ being the distance from the mean intermembrane (T cellAntigen Presenting Cell) separation distance. The crossover from this shorter to a longer time regime leads to a universality in the dynamics, at which point the survival probability shows a different power-law scaling compared to the one at shorter timescales. In biological terms, such a crossover indicates that the TCRpMHC bond has a survival probability with a slower decay rate than the longer LFA-1ICAM-1 bond justifying its stability.