Close Contact Fluctuations: Time of Contact

The letter resolves the long standing debate as to the proper time scale (< τ >) of the onset of the immunological synapse (IS) bond, the non-covalent chemical bond defining the immune pathways involving T-cells and antigen presenting cells (APC). Results from our model calculations show < τ > to be of the order of seconds instead of minutes. Close to the linearly stable regime, we show that in between the two critical spatial thresholds defined by the integrin:ligand pair (∆2 ∼ 40-45 nm) and the T cell receptor (TCR):pMHC bond (∆1 ∼ 14-15 nm), < τ > grows monotonically with increasing co-receptor bond length separation δ (= ∆2 − ∆1 ∼ 26-30 nm) while < τ > decays with ∆1 for fixed ∆2. The non-universal δ-dependent power-law structure of the probability density function (PDF) further explains why only the TCR:pMHC bond is a likely candidate to form a stable synapse.