Differential signaling through the Ig‐α and Ig‐β components of the B cell antigen receptor

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Abstract
The B cell antigen receptor is a complex containing the antigen-binding immunoglobulin molecules and the Ig-α/Ig-β heterodimer which presumably connects the B cell antigen receptor to intracellular signaling components. To analyze the functional properties of the cytoplasmic parts of the B cell antigen receptor, we used the K46 B lymphoma line (IgG2a, χ) to express chimeric molecules composed of the extracellular and transmembrane part of the CD8α molecule and the cytoplasmic sequence of either the Ig-α (CD8α/Ig-α), the Ig-β (CD8α/Ig-β) protein or the membrane-bound γ2a heavy chain (CD8α/γ2a). From these three types of chimeric molecules only CD8α/Ig-α and CD8α/Ig-β, but not CD8α/γ2a, could transduce signals, thus providing the first evidence that the cytoplasmic tail of Ig-α and Ig-β have a signaling capacity. After cross-linking with anti-CD8α antibodies, both molecules induced a similar increase in intracellular free calcium ion and in MAP kinase phosphorylation. Protein tyrosine kinases, however, were strongly activated via the CD8α/Ig-α and only marginally via the CD8α/Ig-β molecule. This suggests that the Ig-α and Ig-β proteins have distinct roles during signal transduction through the B cell antigen receptor.