Immune suppression

Immune responses can be suppressed by a variety of
mechanisms, and some examples follow.
1 Oxidant secretory products of phagocytic leucocytes
suppress the functional activity of lymphocytes
(both B and T cells) and natural killer
cells (El-Hag et al., 1986).
2 Suppressor T cells release inhibitory cytokines,
such as TGF-β.
3 IL-2 regulates the expression of its own receptors
on T lymphocytes.
4 High concentrations of soluble antibody block
the antigen-recognizing receptors (membranebound
antibody) on B lymphocytes. The consequent
inability of the B cells to recognize their
specifi c antigen renders them unable to differentiate
and produce soluble antibody.
5 Antibodies may be regulated by idiotype–antiidiotype
interactions.
6 Macrophages can produce prostaglandins, which
non-specifi cally inhibit lymphocyte responses.
7 Cortisol inhibits the proliferation of lymphocytes
and induces the production of TGF-β.
Histamine, after fi rst mediating the immune response,
helps to suppress it by activating suppressor
T cells that have H2 receptors (Griswold et al., 1984,
1986). In neutrophils, stimulation of H2 receptors by
histamine promotes an increase in intracellular levels
of cyclic AMP, which lowers chemotactic responsiveness
(Anderson et al., 1977) and inhibits release of
lysosomal enzymes (Busse & Sosman, 1976).