Figure 6-10
• Phosphorylation of tyrosine residues within the accessory chains’ ITAMS represents the first BCR/TCR-mediated intracellular event following antigen receptor stimulation.
• This initial phosphorylation is carried out by Src-family kinases: Fyn, Blk and Lyn in B-cells and Lck and Fyn in T-cells.
• In B cells, these kinases associate with the ITAMs of the Igα and Igβ chains through (1) low affinity interactions with their amino-terminal domains or (2) single pTyr ITAMs via SH2 domains (shown here).
• Clustering of BCRs brings many of these associated Src kinases together where they can phosphorylate each other and also the ITAMs of Igα and Igβ.
• Phosphorylation of a single tyrosine in these ITAMs allows tighter binding of Src kinases through their SH2 domains. These bound kinases act to phosphorylate more neighboring ITAMs and provide substrates for Syk
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