Unless you are enamoured with Caravaggio’s 1607 depiction of Flagellazione de Cristo, or you routinely engage in kinky after dark activities, then you might be unaware that the term flagellation derives from the Latin flagellum, which means whip. Yet flagella (plural whips) are all around us, and disturbingly for the prudish among us, these whips are rife within our bedrooms.
Research just published in Nature Medicine indicates that flagella might be a key agent responsible for your next asthma attack.
Microbiologists use the term flagella to describe the locomotive little tails that some bacteria possess. These outboard motors of the bacterial world are rather primitive devices that functionally resemble the flagellation we might be more accustomed to seeing after a good old fertility test, i.e. the tail of sperm cells, not the in-house entertainment at the fertility clinic. Even when they function correctly these tails can seem to rotate around rather haphazardly, but without them bacteria are immobile and dependent on external factors for their trafficking around the world and around your body.
So what do these little bacterial whips have to do with asthma?
Although there are a number of triggers for asthma attack, any sufferer will be able to tell you that one of the key triggers is house dust. When dust is inhaled by an asthmatic an allergic inflammatory response can ensue. However, dust is a multi-component substance.
What is dust?
And which components are allergenic and asthma inducing?
House dust contains fibres from clothing and carpet as well as cat and dog hairs, but it also contains large quantities of human hair and sloughed skin that we shed continually.
Every time you scratch, every time you change clothes, while you sleep, all the time, you are shedding. If you did not continually shed, then you would have to episodically lose an entire skin, like a snake. While it might seem impractical and rather annoying to have to remove your skin like a set of pantyhose, there would be the added benefit of less house dusting. And if there was less dust in your bedroom then there would also be fewer of these nasty little human skin addicts … House Dust Mites.
It is estimated (by me) that there are more House Dust Mites in your bed than there are bloggers on wordpress.com.
It has long been known that House Dust Mites and their ‘faeces’ are responsible for dust-induced asthma attacks. But are the House Dust Mites all to blame? After all it is not their fault that they hold the mantle of ‘ugliest creature you ever slept with’. You shedding your skin all over the place in bite size pieces is like an open invitation for all and sundry to your bed. Further more, it appears that the dust mites might themselves bear unwanted bed mates of their own.
This month a research team led by Donald Cook at the laboratory of Respiratory Biology at the National Institutes of Health in the USA report that a key asthma exacerbating component in house dust is a bacterial protein called flagellin. Just as it sounds, flagellin is the subunit protein that polymerises to form the flagellar whips of certain bacterial species.
Flagellin is one of a group of bacterial proteins that is readily targeted for attack by the human immune system, specifically by an immune cell protein called Toll-like receptor 5 or TLR5. Under normal circumstances this recognition of flagellar bacteria helps us to defeat pathogenic infection by activating the immune system. But allergies occur when the immune system attacks innocuous particles like pollen or nut components. When House Dust Mite ‘faeces’ containing flagellin is inhaled, the researchers say a TLR5-dependent sensitising reaction follows. This then primes the allergic response to other innocuous components of the dust.
Evidently asthmatics should cease their incessant inhalation of dust mite shite. This faecal high is a risky venture.
The researchers suggest that bacterial flagellin is the previously unknown key adjuvant (see Techno box) in house dust that exacerbates allergic asthma.
Without flagellin present in dust one might expect us to ignore the dust. Which is exactly what most of us do anyway. I often discover dust behind the television, under the bed, on the light fixtures, but unless the in-laws are visiting, this dust is part and parcel with the walls, floors, and fittings. My house is veritably brimming with faecal-dwelling whips.
So, why do only some of us become allergic?
This research has added a piece to the puzzle, but the short answer is that we still don’t know. Clearly genetics plays some part, as does allergen exposure and the stage of life one is exposed. It was more than twenty years ago that David Strachan published the Hygiene Hypothesis in the BMJ, but still we can’t solve the puzzle, and so we still cannot instruct people how to avoid acquiring allergic disorders in the first place.
If you believe the Hygiene Hypothesis then I would suggest the best parental course of action is to give your kids a good whipping. If you expose the little mites to a good bit of flagellation at an early enough age then perhaps dust will just be dust and what goes on in their beds need never be the source of a dinner table conversation.
Unfortunately for people who have already developed allergic asthma their lives consist of avoiding dusty flagellation which means constantly heat treating their bedding, vacuuming and other undesirable house duties. Hopefully scientists will now be able to build on the knowledge that flagellin is the key adjuvant in dust, and so come up with an explanation of the modern surge in allergic asthma, one that gives parents an adequate set of instructions for prevention rather than treatment.
As an aside, the Flagellazione di Cristo might now be re-interpreted as a metaphor; perhaps an acute bout of bacterial induced asthma prior to crucifixion. Christian art and history does indeed depict Pontius Pilate, in his elegance, as reminiscent of a House Dust Mite.
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