4.1.8 The B Lymphocyte Response

Question 1

Describe the maturation of B lymphocytes.

Answer 1

B-lymphocytes (B cells) remain in the bone marrow until they are mature and then spread through the body, concentrating in lymph nodes and the spleen

During the process of maturation B cells gain specific cell surface receptors called B cell receptors (BCRs)
The receptors on the cell surface of B cells are antibodies and are sometimes referred to as antibody receptors
Part of each antibody molecule forms a glycoprotein receptor that can combine specifically with one type of antigen
A small number of B cells have the same BCRs, these genetically identical cells are called a clone

Question 2

Describe the role of B cells in the immune response.

Answer 2

In order to play their role in the immune response B cells need to be activated and increase in number; this occurs as follows:

Clonal selection and activation:
B cells with complementary antibody receptors bind to antigens on antigen presenting cells; this is clonal selection
These antigen presenting cells can be phagocytes, infected cells, or the pathogens themselves
This binding, together with interleukins released by T helper cells activates the B cells

Clonal expansion:
Activated B cells divide by mitosis to produce clones
This results in large numbers of identical B-lymphocytes being produced over a few weeks
Some of these B-lymphocytes differentiate into plasma cells
Plasma cells secrete lots of antibody molecules (specific to the antigen) into the blood, lymph or linings of the lungs and the gut
The other B-lymphocytes become memory cells that remain circulating in the blood for a long time