The supramolecular activation cluster (SMAC) forms at the point of contact between a T cell and an antigen-presenting cell (APC). The term "immune synapse" has provided a useful analogy by which to describe the SMAC in CD4 T cells, although it has not been clear whether this terminology could reasonably be extended to other types of T cells.
Using three-dimensional digital microscopy, Potter et al. observed that SMAC formation also occurs in CD8 T cells and that, as with their CD4 counterparts, this requires a sufficient concentration of specific antigen displayed by the APC. In CD8 and CD4 T cells, SMACs were organized similarly, exhibiting central and peripheral domains containing signaling and adhesion proteins, such as protein kinase C and the integrin LFA-1, respectively. However, CD8 T cells appeared to differ from CD4 T cells in that engagement of the CD8 coreceptor presented an obligatory step in SMAC formation. Extension of the immune synapse model to CD8 T cells may help to unravel the programs of activation followed by these cells. -- SJS
Proc. Natl. Acad. Sci. U.S.A. 98, 12624 (2001).
