The Immunological Synapse

Immunological responses, both involve close contact between a T cell and an antigen-presenting cell (APC).


Electron microscopy (right) and several types of light microscopy have shown that these interactions involve a tight union between the two types of cells. This has been named the immunological synapse in recognition of the several ways in which it resembles the synapses of the nervous system.

The electron micrograph (courtesy of J. W. Uhr) shows a B cell and T cell bound to each other. The bar = 1 μm.

A number of pairs of molecules participate in the formation of the immunological synapse.

TCR/MHC-peptide pair

Costimulatory pairs

such as

General adhesion molecules

Cytokine receptors

Cytokine receptors also cluster in the synapse (not shown in the diagram) where they are exposed to cytokines secreted into the synapse.

Formation of an immunological synapse causes the T cell to

B cells can also form an immunological synapse

While B cells can bind soluble antigens with their antigen receptors (BCRs), they can also bind antigens attached to the surface of dendritic cells. In doing so, they form an immunological synapse similar to that of B cell/T cell synapse.

Why an immunological synapse?

The molecules released by effector T cells (e.g., interleukins, perforin) are potent cytokines. Confining them to the immunological synapse ensures that they will not act nonspecifically against innocent bystander cells.

As for B cells and antigen-presenting dendritic cells, synapse formation appears to be a mechanism to cluster the antigens and BCRs in a small area, which enhances activation of the B cell.


Antigen-presenting cells like can also present antigen to T cells by means of exosomes. These are tiny membrane-enclosed vesicles released by the cell. Their surface is studded with MHC-peptide complexes [View].

Antigen-presentation by exosomes may in some cases inhibit — rather than stimulate — an immune response.

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31 December 2012