[1][2] It offers an explanation for how TCR binding to its ligand triggers T-cell activation, based on size-sensitivity for the molecules involved.
[3] Phosphatases CD45 and CD148 with much larger ectodomains than TCR are sterically excluded from the close contact zones, while the region is still accessible for the small kinase Lck.
When T-cell and APC membranes separate, the close-contact zone vanishes and large-ectodomain tyrosine phosphatases are allowed to restore the ground state.
[4][5] It was also shown that both the truncation of CD45 and CD148 (hence are able to enter the close contact zone) and the elongation of the MHC inhibit TCR triggering.
Kinetic-segregation model uses here the same explanation as it provides for low net phosphorylation of TCR in the resting T-cell described previously.
Immobilized superagonistic antibodies bound to CD28 exclude CD45 phosphatases completely and the signal leading to T-cell activation is stronger.