Selenocysteine, the selenoproteins of white blood cells and the one EU sentence linking selenium and the immune system, walked through one at a time.
Open the Pocket GuideIn the genetic code, the letter sequence UGA ordinarily means one thing: the protein chain stops here. In a small group of human genes, however, the cell reads on past this point and slots in an unusual building block.
That building block is called selenocysteine. It resembles the familiar amino acid cysteine but has a selenium atom where cysteine has a sulfur atom. For the cell to reinterpret the stop signal, the matching messenger RNA needs a folded stem-loop structure near its far end, known as the SECIS element, plus a dedicated transfer RNA that delivers selenocysteine.
Twenty-five selenoprotein genes have been described in the human genome. Several of them are expressed in lymphocytes, macrophages and neutrophils. Benitoitera puts these proteins front and center: where they sit in the cell, which biochemical tasks have been documented, and what the authorized EU claim says about them – and what it leaves unsaid.
The examples below come from basic research in biochemistry and immunology. They show why scientists take an interest in selenium in connection with immune cells, and they form the backdrop to the longer pocket guide.
Selenoprotein K is a small membrane protein in the endoplasmic reticulum, the cell’s internal calcium store. Working with an enzyme called DHHC6, it attaches a fatty acid chain to the IP3 receptor, a channel that lets calcium out of this store. Without that modification, less calcium flows into the cell interior when a signal arrives.
In T lymphocytes, macrophages and neutrophils, calcium signals direct a wide range of processes, such as directed movement or the reading of particular genes. In experiments with mice lacking selenoprotein K, this calcium influx was reduced in several types of immune cells.
Glutathione peroxidase 4 (GPx4) has selenocysteine in its active site and converts peroxides right inside the fatty acid chains of cell membranes. Activated T lymphocytes divide quickly and keep building new membranes as they do. In mouse models whose T cells lacked GPx4, these cells were lost after activation through an iron-dependent form of cell death called ferroptosis.
Most tissues do not get their selenium straight from food but by way of selenoprotein P. The liver makes this plasma protein, which holds up to ten selenocysteine residues, and releases it into the blood; target cells take it up through receptors on their surface. When selenium is scarce, the cell shares it out according to an observable order of priority: some selenoproteins continue to be made, others in clearly smaller amounts.
For this subject area, the Union list contains exactly one sentence, which followed an opinion from the European Food Safety Authority: Selenium contributes to the normal function of the immune system. EU-authorized wording · Regulation (EU) No 432/2012. Selenoprotein K, GPx4 and selenoprotein P add laboratory context to it; we draw nothing from them beyond that sentence.
A few pointers first, to make the rest easier to follow: the element itself, the form in which it appears in proteins, and the scope of the EU claim.
With atomic number 34, selenium belongs to the same main group as sulfur and oxygen. The body uses it almost entirely in protein-bound form, which is why people have to take it in through their diet. The EU reference intake used for nutrition labeling is 55 micrograms per day.
Selenium contributes to the normal function of the immune system.
EU-authorized wording · Regulation (EU) No 432/2012The selenium atom makes the side chain more reactive than the sulfur group of cysteine. That is why many selenoproteins are enzymes that pass electrons along. To insert it, the cell runs its own machinery made up of a special transfer RNA, binding proteins and the SECIS element.
It refers to the ordinary workings of the immune system, provided enough selenium is taken in. The sentence says nothing about diseases, about doses, or about anything beyond the body’s everyday state.
A selenoprotein table, background on selenoprotein K and GPx4, notes on intake and annotated references – delivered as a digital document for reading on screen.
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The texts published by Benitoitera offer general information on nutrition science and biochemistry. They are not medical advice, and they are no basis for reaching a diagnosis or for starting, changing or stopping any therapy.
If you have symptoms or a pre-existing condition, are pregnant or breastfeeding, or take medication on a regular basis, any question about your selenium intake belongs in the hands of a physician or pharmacist.
A dietary supplement is no substitute for a varied, balanced diet and a healthy daily routine. The daily amount printed on the package is a ceiling that should not be exceeded, and supplements must be stored out of the reach of young children. With selenium this deserves extra attention, since the tolerable upper limit lies not far above the amount the body needs. These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
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