Final answer:
The B-cell co-receptor is composed of CR2 (CD21), CD19, and CD81 (option d) , which collectively aid in B cell activation and immune response enhancement.
Step-by-step explanation:
The B-cell co-receptor is a complex of three proteins that helps in the activation of B cells, which are crucial for the adaptive immune response. The correct composition of the B-cell co-receptor is CR2 (CD21), CD19, and CD81. These proteins work together to lower the threshold for B cell activation by binding to complement-decorated antigens and aiding the B-cell receptor (BCR) to activate the B cell after antigen recognition.
The correct answer to the question is d. CR2 ; CD19 ; CD81. This combination of molecules helps B cells to recognize antigens more efficiently, enhancing the immune response. BCRs are membrane-bound immunoglobulins, specifically IgD and IgM, that bind specific antigen epitopes with their Fab antigen-binding regions.