Figure 6.

Model for IS formation by helper T cells and CTLs. Based on prior reports, the helper T cells migrate on substrates with ICAM-1 (dark gray) alone. When agonist MHCp complexes are encountered, the cells form a nascent IS with ICAM-1 in the center and MHCp complexes (light gray) on the periphery. This pattern then inverts to form the mature IS with ICAM-1 in a ring and MHCp complexes in the center. Based on this study, we propose that CTLs on ICAM-1 alone alternate about four times per hour between ring junctions in which ICAM-1 is organized in a ring and typical migratory morphology. We propose that the CTL ring junction constitutes a functional “presynapse” that intensifies immune surveillance. When antigen is encountered, CTLs form an IS without going through distinct nascent and mature stages. We propose that this “short cut” saves the CTL time and ensures that an adhesive “gasket” is formed before cytolytic substances are released into the synaptic cleft.