Because of the 2D nature of the receptor clusters, the lateral component of toxin transport is more severely hindered than the perpendicular one (length of an Fab or Fc fragment is $6.5 nm; the length of the portion of MHCI or MHCII protruding from the membrane plane is $10 nm). B Illustration of the principle of detection of proximity between two cell-surface receptors (here MHCI and MHCII), one of which (MHCII) when liganded is capable of modulating channel current via some signaling mechanism by retarding ligand (L243 mAb) binding to the ''electrically active'' receptor (MHCII) by a nanoparticle bound to another receptor (MHCI) in close proximity