Activin enhances FSH biosynthesis and secretion, and participates in the regulation of the menstrual cycle. Conversely, inhibin downregulates FSH synthesis and inhibits FSH secretion. Inhibin A is part of the prenatal quad screen administered during pregnancy at a gestational age of 16-18 weeks. An elevated inhibin A (along with an increased beta-hCG, decreased AFP, and a decreased estriol) is suggestive of the presence of a fetus with Down syndrome.
Many other functions have been found to be exerted by activin, including roles in cell proliferation, differentiation, apoptosis, immune responses, and wound repair.
Activin is a dimer composed of 2 identical or very similar beta subunits. Inhibin is also a dimer wherein the first component is a beta subunit similar or identical to the beta subunit in activin.
Schematic diagram of the structures of inhibin and activin. The black line between the monomers represents a disulfide bond. Image source: Wikipedia, public domain.
How does this relate to asthma?
Like many cytokines, activin-A triggers different effects in different situations. It incites inflammation but it can inhibit it as well.
Injections of activin-A helped mice breathe easier: Activin-A exerted its effects by boosting the number of T reg cells.
T reg cells work by releasing soothing cytokines IL-10, TGF-1 & blocking maturation of dendritic cells, essential for Th2 specialization.
References:
Activin eases asthma: Mysterious cytokine quells asthma, triggers T reg cells to prevent dendritic cells from growing up http://is.gd/26Pu0
Activin and inhibin, from Wikipedia, the free encyclopedia.Activin-A - a new critical regulator of allergic asthma http://goo.gl/5Pm9I - Potential therapeutic target.
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