Trigger for nickel allergies discovered

By Enda Shevlin

It is often said that women have expensive tastes. But taste does not necessarily equate to means, forcing many cash-strapped young ladies to resort to wearing fake jewellery. It is often the case that women, when wearing fake or impure jewellery, break out in an itchy rash, known as contact sensitivity. The reason for this uncomfortable effect is that fake jewellery is often made from an inexpensive nickel core coated in an alluring gold or silver veneer. Nine times out of ten they are indistinguishable from the real thing, until the itching starts.

Tiny amounts of perspiration corrode the underlying nickel of the faux-gold and silver jewellery during wear, releasing salts or “ions” of the same which triggers an allergic response, resulting in an ugly rash.

In the end, all allergic reactions have a trigger as their source. In this case it is nickel, which in some way agitates the immune system, causing it to awaken and destroy the allergen as if it were a virus – even though in reality, allergens often pose no systemic threat to our health. Immunologists, who study the immune system at the level of atoms and molecules, have recently discovered exactly why a large portion of humans respond to the nickel allergen as if it were an infection, and have documented their findings in Nature Immunology.

Our immune cells use many different surface receptors to sense potential danger but among the most fundamental are the “Toll-like receptors” or TLRs, so called because the German scientists who discovered it, exclaimed “Toll!”, the German word for “great”. If one were to imagine our bodies being locked in a war against harmful microorganisms, our tissues and organs would be the battlefield, the immune cells would be our soldiers and TLRs would act as lookouts for invading enemy bacteria and viruses.

What has been discovered for the first time by Marc Schmidt and his colleagues in Germany is that one particular TLR, TLR4, which normally senses harmful bacteria, has the additional function of specifically recognising the same nickel contained in any fake jewellery, be it a pair of earrings, a bracelet or a watch.

Doing what it is supposed to do, upon activation by the nickel ion, the TLR directs an inflammatory immune response, producing the offending rash. The researchers narrowed the pathway down to the individual molecules that sense nickel and found that mice, which are not normally allergic to nickel, whose immune cells were engineered to express human TLR4 on their surfaces, would suddenly develop allergic responses.

This groundbreaking study into the causes of allergic responses is quite revolutionary. It opens up another avenue of thought about how the immune system recognises various allergens, an important step in figuring out how to reduce or eliminate their negative effects on humans. Researchers hope to repeat their success in future by isolating other allergens in a similar fashion.

But of immediate importance, now that the exact mechanism of sensitivity has been discovered, there is now a specific drug target for the future prevention of nickel based allergies: any drug that can block the TLR4-nickel interaction will also prevent, or at least significantly reduce, the symptoms of nickel allergy in humans.

Good news for anyone with a soft spot for shiny trinkets but a softer spot for a bargain.