Overview
Immune responses depend on communication between cells: antigen-presenting cells, T lymphocytes and B lymphocytes talk to each other by direct contact (receptors, co-stimulatory molecules) and by soluble messengers, the cytokines. This topic follows how T and B cells are activated in the peripheral lymphoid organs and how cytokines coordinate the response.
- Overview of Peripheral Lymphoid Organs
- Main Sites: Lymph nodes, spleen, and mucosa-associated lymphoid tissue (MALT).
- Function: These organs host immune responses. Here, B- and T-lymphocytes, having matured in central lymphoid organs (bone marrow for B-cells, thymus for T-cells), encounter antigens and are activated.
- Activation: Lymphocytes proliferate into clones and differentiate into effector and memory cells in response to antigens.
- B and T lymphocytes complete their development and become immunocompetent in the central lymphoid organs (bone marrow for B cells and thymus for T cells).
- These immunocompetent cells then migrate to peripheral lymphoid organs where they participate in immune responses upon encountering antigens.
- These organs are the primary sites for initiation and regulation of immune responses.
- Lymphocytes in these organs become activated upon recognizing antigens.
- Activated lymphocytes undergo clonal proliferation and antigen-specific differentiation into effector cells (that eliminate pathogens) and memory cells (that persist for future immune responses).
- This process is antigen-dependent, unlike their earlier maturation which is antigen-independent.
- Effective immune responses depend on interactions between B cells, T cells, and antigen-presenting cells, all coordinated by signaling molecules called cytokines.