Control of the Immune Processes
Network Theory
The immune system is viewed as an interacting network of lymphocytes and antibody (Ab) molecules that possess variable (V) regions. This theory involves coordinated roles for B cells that produce antibodies, T cells that regulate antibody production by B cells, and non‑specific accessory cells (A cells).
The "recognizers" of the immune system—lymphocytes and antibodies—not only recognize foreign particles but also recognize and interact with each other as components of this network. Antibodies are capable of recognizing an almost unlimited number of different substances, and this recognition
includes the variable regions of other antibodies, leading to the formation of anti‑antibodies. Thus, Ab V regions bind not only foreign antigens but also other V regions within the immune system. The immune system is therefore conceptualized as a network interconnected by V–V interactions.
Helper–Suppressor Theory
CD8+ suppressor T‑cell populations possess antigen‑specific suppressive activity and can be transferred between animals, indicating an active regulatory role in immune control.
Th1–Th2 Theory This theory proposes a major subdivision of mouse CD4+ T‑helper cell clones based on their cytokine secretion patterns:
- Th1 cells secrete IL‑2 and IFN‑γ.
- Th2 cells secrete IL‑4 and IL‑5. Similar functional phenotypes have been identified in human T‑cell clones.
Activation and Inhibition Signal Theory
After a prolonged period of relative dormancy, suppressive T cells with antigen‑specific receptors were rediscovered. Evidence accumulated for active, transferable, antigen‑specific suppressive T‑cell activity. A high frequency of autoimmunity was observed in experimental animals, particularly:
- Thymectomized mice
- Cytokine or cytokine‑receptor gene knockout mice