Question

B lymphocyte antigen receptor signaling is modulated by a co-receptor complex of at least three cell-surface molecules that can be co-ligated with the B cell receptor. These molecules have been shown to increase the activatory signal after antigen binds to immunoglobulin on the B cell surface. One of these molecules binds iC3b and C3dg and is known as?

CD4
G-CSF
CEA
CR2
LTN

Answer 1

The molecule in the B lymphocyte co-receptor complex that binds iC3b and C3dg is known as CR2 or CD21. It plays a critical role in enhancing BCR signaling and the subsequent immune response, particularly in the context of T cell-dependent antigen activation involving helper T cells.

Step-by-step explanation:

The molecule in the B lymphocyte co-receptor complex that binds iC3b and C3dg, and is involved in modulating the activatory signal after antigen binding, is known as CR2 (also referred to as CD21). CR2/CD21 enhances B cell receptor (BCR) signaling upon co-ligation with immunoglobulin on B cells' surface. This process is crucial for the adaptive immune response, where B-cell receptors on naive mature B cells, which are membrane-bound monomeric forms of IgD and IgM, bind specific antigen epitopes with their Fab antigen-binding region and initiate a series of cellular events leading to the B cell's activation.

In the presence of T cell-dependent antigens, such activation requires cooperation with helper T cells via linked recognition and cytokine signaling to achieve full activation and differentiation of B cells into antibody-secreting plasma cells.