Page 404 - Veterinary Immunology, 10th Edition

VetBooks.ir Immunological Synapse Formation

Cell membranes consist of fluid lipid bilayers that contain
segregated areas called lipid rafts, where patches in the membrane

are enriched in sphingolipids, cholesterol, and proteins. Small rafts
are distributed evenly over the surface of resting T cells. When a T
cell and an antigen-presenting cell come into contact, their cell
membrane rafts aggregate so that the TCR-peptide-MHC complexes
and the co-stimulatory receptors cluster together in the area of

contact to form an immunological synapse (Fig. 14.9). This synapse
consists of concentric rings of molecular complexes called
supramolecular activation clusters (SMACs). They form a

characteristic “bull's eye structure” consisting of a central (c) SMAC
surrounded by a peripheral (p) SMAC and an outer ring. The
cSMAC of Th1 cells contains the MHC and TCR molecules as well
as CD4, CD3, CD2, CD28, CD80/86, and CD40/154. The pSMAC
contains CD45, the adhesion molecule ICAM-1 and leukocyte

function-associated antigen-1 (LFA-1). The third, outer ring
contains proteins excluded from the central synapse such as CD43.
(CD43 is a very large antiadhesive molecule that could interfere

with the functioning of the synapse.)

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