Lymphocyte Activation: Signal Transduction


Adaptive immunity depends on the transfer of information across the plasma membrane of T and B lymphocytes. This information takes the form of signal transduction pathways that are initiated by the recognition of antigens by specific transmembrane receptors, and that result in a complex series of biochemical changes within the cell that ultimately alter cellular function. A key feature of antigen receptors on T and B lymphocytes is that they contain no intrinsic catalytic activity. Rather, they signal through the initial activation of nonreceptor tyrosine kinases, which then phosphorylate various cytoplasmic and membrane‐bound adaptor proteins. These adaptor proteins function as molecular scaffolds for the further activation of downstream signalling pathways that mediate the ultimate effects of antigen recognition on lymphocyte function, including modification of transcription factors and changes in the cytoskeleton.

Key Concepts:

  • Lymphocyte antigen receptors consist of separate modules for antigen recognition and signal transduction.

  • Lymphocyte antigen receptors contain no intrinsic catalytic activity, but rather link to nonreceptor tyrosine kinases.

  • The immunoreceptor tyrosine‐based activation motif is critical for linking antigen receptors to tyrosine kinases.

  • Both cytoplasmic and transmembrane adaptor proteins are important for translating proximal antigen receptor signalling to common downstream signalling pathways.

  • Downstream effectors of antigen receptor signalling include serine/threonine kinases and small G proteins.

  • Antigen‐receptor signalling can be modulated by other coreceptors expressed by lymphocytes.

  • Antigen‐receptor signalling is critical for both activation of mature lymphocytes as well as for their development in the bone marrow or thymus.

Keywords: signal transduction; lymphocytes; receptors; phosphorylation; immunity

Figure 1.

The signalling pathways following BCR stimulation. Molecules in red are major signalling components that are phosphorylated after BCR crosslinking. Arrows represent either phosphorylation induced after BCR ligation or connection between signalling molecules and downstream events or components. Coreceptors that play regulatory roles in BCR signalling are shown in colour.

Figure 2.

The signalling cascades activated by the TCR. The major signalling molecules that become tyrosine phosphorylated following TCR‐CD4/CD8 crosslinking are shown in red.

Figure 3.

Putative phosphatidylinositol pathway and calcium flux induced by crosslinking of the BCR or TCR.



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P Kane, Lawrence(May 2013) Lymphocyte Activation: Signal Transduction. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0001185.pub3]