Question

Which of the following types of B-cells would be considered the “youngest” type and the "oldest" type?  

a. Effector B-cell

b. Immature B-cell

c. Naive B-cell

Answer 1

B cells are lymphocytes involved in humoral immune response. They are stimulated by pathogen via their antigens to produce antibodies that bind to the antigen, leading to killing of the phagocytes.

Initial B cell development occurs in fetal liver. In adults, the bone marrow is the site for B cell development. B cells are produced from hematopoietic stem cells in the bone marrow. Hematopoietic stem cells will form the pre-pro-B cell. These cells show D-J recombination (also seen in common lymphoid progenitors). V-DJ recombination is seen in pro-B cells that are formed from pre-pro-B cells. Pro-B cells form the pre-B cells where there is later formation of the pre-B cell receptor. The pre-B cells later develop to small pre-B cells, which then form B cells that express IgM on their surface. These IgM expressing B cells will enter the spleen where they will under later developmental stages to gain B cell function. The B cell entering the spleen has a functional B cell receptor. They will form T1 B cell and the T2 B cells (transitional stages of B cells). T2 B cells form T3 B cells or MZ B cell (marginal zone B cells) or Fo B cell (long lived follicular B cells).

Immature B cells are B cells that originate from pre-B cells. They are sensitive to antigen binding. If antigen binds, then they die. Mature naïve B cells are cells that express IgD and IgM along with m chain. Naïve B cells are produced from immature B cells. Naïve B cells are present in the peripheral circulation. Naïve B cells are B cells that have not reacted with antigen. Once an antigen binds to naïve B cell, they will differentiate into memory B cell or the plasma cells that produce antibodies against the antigen. Plasma cells that produce antibodies are known as the effector B cells. They are required to clear the infections as the antibodies produced are specific against the infection.

Thus, immature B cells are the oldest B cells as they form first while effector B cell are the youngest B cells as they form last in the B cell development.

Right choice:

Oldest type: b. Immature B cell

Youngest type: a. Effector B cells