Clonal expansion

Clonal Expansion is a fundamental process in the immune system where a specific B cell or T cell is selected for replication due to its ability to bind to an antigen. This process is crucial for the adaptive immune response, as it allows for the rapid multiplication of specific immune cells that can recognize and respond to invading pathogens.

Overview

The process of clonal expansion begins when a lymphocyte encounters an antigen that matches its specific antigen receptor. This encounter triggers the lymphocyte to proliferate and differentiate into a clone of identical cells, all bearing the same antigen receptor. This process is known as clonal selection.

Clonal Selection

Clonal selection is the theory that explains how a single B or T cell that recognizes an antigen proliferates to produce a population of identical cells. The theory was first proposed by Frank Macfarlane Burnet in the 1950s. According to this theory, each lymphocyte bears a unique antigen receptor. When a lymphocyte encounters an antigen that matches its receptor, it is stimulated to proliferate and differentiate.

Clonal Expansion in B Cells

In B cells, clonal expansion occurs in the germinal center of the lymph node. When a B cell encounters its specific antigen, it is stimulated to proliferate and differentiate into plasma cells and memory B cells. Plasma cells are the effector cells of the B cell response, producing antibodies that can neutralize the antigen. Memory B cells, on the other hand, persist in the body and provide long-term immunity.

Clonal Expansion in T Cells

In T cells, clonal expansion occurs in the thymus or peripheral lymphoid tissues. When a T cell encounters its specific antigen, it is stimulated to proliferate and differentiate into effector T cells and memory T cells. Effector T cells carry out the immediate response to the antigen, while memory T cells provide long-term immunity.

Importance of Clonal Expansion

Clonal expansion is crucial for the adaptive immune response. It allows for the rapid multiplication of specific immune cells that can recognize and respond to invading pathogens. Moreover, it provides long-term immunity by generating memory cells that can quickly respond to future encounters with the same antigen.