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Macrophage migration inhibitory factor (MIF) was one of the first cytokines to be discovered. During the years MIF was found to play an important role in pathogenesis of autoimmune diseases, in sepsis as well as in angiogenesis, tumorigenesis and growth regulation and has an endocrine and enzymatic function.
MIF is a pluripotent cytokine that regulates inflammatory and immune responses. It is produced by peripheral immune cells and also by endocrine cells in the anterior pituitary gland. MIF exerts its pro-inflammatory actions in the host defense system by blocking the inhibitory effects of glucocorticoids on the release of other pro-inflammatory cytokines (e.g.
IL-1, IL-6, TNF-a). Unique is a biphasic, bell-shaped concentration-dependent regulation: MIF release is stimulated by very low concentrations of glucocorticoids while higher concentrations have no effect on MIF secretion. These special interaction was so far only detected in the periphery on a local level not in a central superordinate system.
The aim of the present study was to get more information about detection, secretion and regulation of MIF after treatment with Dexamethason (DEX) in AtT20 (murine corticotrope pituitary cell line), HN10e (murine hypothalamic cell line) and primary cultures of hypothalamic and cortical neurons from rat embryos.
The immunohistochemical results show that MIF is expressed in all examined cells. There is a strong presence in nuclear structures. This contains a reference to the role of MIF in cell cycle control and growth regulation, a function which has become important in recent publications.
The results of PCR shows that MIF mRNA is continuously expressed on a high level, but there is no transcriptional regulation to be shown. Other authors also believe in posttranscriptional mechanisms: controll of translation, changes in mRNA stability, increased protein turnover, inhibition of secretion.
In the AtT20 cells the Western blot experiment shows no biphasic regulation but indicates a normal concentration-dependent synthesis and secretion: Incubation with the lower DEX concentration (10-11 M) results in an increased intracellular MIF-content after 1 and 4 h, while there is a secretion after 2 and 8 h, with the higher DEX concentration (10-7 M) there is a higher intracellular level after 1, 4 and 8 h, a secretion only after 2 h).
The HN10e cells show that DEX concentration has an influence on time and extent of MIF synthesis and secretion. This provides an indication of a biphasic interaction: After stimulation with DEX 10-11 M there is an increased intracellular concentration of MIF after 1-2 h, with DEX 10-9 M intracellular increase only after 8 h. Secretion of MIF after 8 h with DEX 10-11 M.
The primary cultured cells also give a hint to a possible bell-shaped interaction: In cortical and hippocampal neurons there was a decreasing intracellular concentration of MIF 4 h after incubation with DEX 10-11 M, while there was an increased MIF level 4 h after DEX 10-9 M.