Final answer:
The B cell receptor complex includes additional signaling molecules Igα and Igβ, which form a heterodimer that associates with IgD and IgM to enable signal transduction for B cell activation.
Step-by-step explanation:
The additional components of the B cell receptor (BCR) complex include the signaling molecules immunoglobulin-α (Igα) and immunoglobulin-β (Igβ), which are disulfide-linked together to form a heterodimer. These molecules are necessary because the BCR alone does not have sufficient intracellular signaling domains. The Igα/Igβ heterodimer associates with the membrane-bound immunoglobulins IgD and IgM through their transmembrane and cytoplasmic domains, creating a functional BCR complex capable of transducing signals into the B cell following antigen recognition.
Upon antigen binding to the BCR, the Igα/Igβ heterodimer transmits the signal downstream leading to B cell activation. This interaction is vital for the B cell's development, differentiation, and response to pathogens. Therefore, the inclusion of Igα and Igβ is essential for the full functionality of the BCR complex in immune responses.