The kaleidoscope of glucorticoid effects on immune system.

Glucocorticoids (GCs) are potent anti-inflammatory and immunosuppressive agents which exert multiple effects on immune cell functions. Although their use dates back 60 years, their functions and mode of action have not been completely elucidated yet. GCs act through different genomic and non genomic mechanisms which are mediated by the binding to cytosolic glucocorticoid receptor as well as to cell membrane receptors, or by interacting directly with enzymes and other cell proteins. T cell subtypes have a different sensitivity and response to GCs; in fact, GCs have an immunosuppressive effect on pro-inflammatory T cells, while they stimulate regulatory T cell activity. The effect of GCs on B cells is less clear. Interestingly, treatment with GCs may determine apoptosis of autoreactive B cells by reducing the B cell activator factor (BAFF). Tolerogenic dendritic cells which express low levels of Major Histocompatibility Complex class II, co-stimulatory molecules and cytokines, such as IL-1β, IL-6, and IL-12, can be induced by GCs. GCs at low levels stimulate and at high levels inhibit macrophage activity; moreover, they reduce the number of basophils, stimulate the transcription of inhibitors of leukocyte proteinases and the apoptosis of neutrophils and eosinophils. Finally, GCs inhibit the synthesis and function of some cytokines, particularly T helper type 1 cytokines, and to a lesser extent the secretion of chemokines and co-stimulatory molecules from immune and endothelial cells.