Chapter 15, Problem 1MCQ

The primary B-cell receptor is

1. a. IgD.
2. b. IgA.
3. c. IgE.
4. d. IgG.

Summary Introduction

Introduction:

Immunoglobulins are the glycoprotein molecules which are present in a Y shaped structure. They bind to the antigenic foreign epitopes and inhibit the spread of infection inside the human body. They are composed of one heavy chain and one light chain with variable and constant regions in the polypeptide protein.

Answer to Problem 1MCQ

Correct answer:

The primary B-cell receptor is IgD. Therefore, option (a) is correct.

Option (a) is given as “IgD”.

Explanation of Solution

Justify reason for the correct statement:

In the case of B lymphocytes, the genes code for Ig (immunoglobulins) synthesis, which are the receptors for B-cells. There are antigen binding sites in the ends of forks that are formed by the heavy and light chains and are variable in shape with respect to the shape of antigens. IgDis one of the classes of Igs that is secreted in blood and is present as a part of the membrane surface receptor molecule on $\text{B}$ cells.

Hence, option (a) is correct.

Justify reasons for the incorrect statements:

Option (b) is given as “IgA”.

IgA is secreted in the lactating milk and forms the defense immunity in a child. It is not the primary Ig of B-cell receptors. Hence, it is a wrong answer.

Option (c) is given as “IgE”.

IgE is released from the mast cells following an antigenic response in the human body. It is not the primary Ig of B-cell receptors. Hence, it is a wrong answer.

Option (d) is given as “IgG”.

IgG is the antibody which is formed from activated $\text{B}$ cells and circulates in the blood and body fluids. It is not the primary Ig of B-cell receptors. Hence, it is a wrong answer.

Hence, options (b),(c), and(d) are incorrect.

Conclusion

IgD is the immunoglobulin class that is considered as the primaryreceptor of B-cell.