25.17 : 适应性免疫反应细胞

In the bone marrow, the common lymphoid progenitor cells give rise to precursors for T and B lymphocytes.

Next, these precursors mature to gain immunocompetence or the ability to recognize and respond to specific foreign antigens. They also acquire self-tolerance, which keeps them unresponsive to self-antigens.

B cell precursors undergo maturation in the bone marrow, while T cell precursors migrate to the thymus for maturation.

After 2-3 days, mature but naive lymphocytes leave their maturation sites — thymus and bone marrow — to seed secondary lymphoid organs, such as the spleen and lymph nodes, or circulate in the bloodstream.

These naive T and B lymphocytes become activated upon encountering specific foreign antigens.

Naive T cells require activation assistance from other immune cells, such as B cells, dendritic cells, or macrophages. These cells are called antigen-presenting cells.

An activated lymphocyte rapidly multiplies to form multiple cloned cells with the same antigen specificity.

While most clones become effector cells to clear the infection, a few become memory cells that ensure a faster response upon reinfection.