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Activin A is a protein that triggers activity in many types of cells. Produced in bone marrow cells and immune cells within bone marrow, this protein has a role in regulating follicle stimulating hormone (FSH), triggering the production of hemoglobin, and signaling various types of cells to reproduce. It can also signal dendritic cells to allow immune responses to begin, and plays a role in vascular cell growth. The substance is part of the transforming growth factor beta protein family, and is involved in various developmental, repair, and inflammatory processes in biological tissues.
In addition to playing a role in FSH biosynthesis, activin A has control over the release of hormones such as prolactin, corticotrophin, and oxytocin. The production of endothelins is stimulated by it as well, and the protein helps to prevent the death of neurons. Activin A also regulates vascular smooth muscle cell growth through complex processes involving a variety of other substances.
The immune system relies on a complex interaction of processes to work properly. Activin A functions in B cells at specific stages, aiding their proliferation and antibody secretion, although it inhibits B cell production in bone marrow stem cells. It is not expressed when these cells are active, and also provides a mediation factor for T cells in the immune system. Over-activity of T cells plays a role in allergic reactions involving the airways, so physicians have administered recombinant activin A to suppress the allergic response triggered by certain immune cells.
To detect activin A, a protein binding assay is used. An FSH suppressing protein called follistatin is utilized in the process, and the protein complex is detected through its activity in the sample. In people with asthma, immune cells in the lungs are often unregulated and cause inflammation, and the administering of activin A can mitigate the problem. Treatments for erythroleukemia as well as for inhibiting growth have also involved the use of the protein.
Activin A is also produced in cells besides bone marrow, and has an influence on many activities in neural and endocrine cells. It regulates cell growth and differentiation for a range of cell types, and is one of three forms of activins which also include activin B and activin AB. The differentiation of various blood cells is also controlled by the protein, as well as the formation of granulose cells, which surround a female egg.