A study shows that there are two molecular pathways for conveying sensations of itching, with the itching of severe eczema following an unexpected route.
In normal eczema, cells in the skin convey the itching sensation, releasing histamines. This can be blocked with antihistamines.
“Years ago, we used to think that itch and pain were carried along the same subway lines in the nerves to the brain, but it turned out they weren’t, and these new findings show there’s another pathway entirely that’s causing these episodes of acute itching in eczema patients,” said principal investigator Brian S Kim, MD, Washington University School of Medicine. “The itch can be maddening. Patients may rate their chronic itch at around a 5 on a scale of 10, but that goes up to 10 during acute itch flares. Now that we know those acute flares are being transmitted in an entirely different way, we can target that pathway, and maybe we can help those patients.”
With severe itching in eczema, different cells in the blood are activated, transmitting great quantities of non-histamine molecules which also convey the itching sensation. This renders antihistamines usesles in trying to control the itch. The discovery of this new pathway offers new possibilities for treating other conditions as well. Recent studies have tried to block Immunoglobulin E (IgE) in response to allergies.
“We’ve connected acute itching in eczema to allergic reactions transmitted by an entirely different population of cells,” explained Kim. “In patients who experience episodes of acute itching, their bodies react in the same way as in people with acute allergy. If we can block this pathway with drugs, it might represent a strategy for treating not only itch but other problems, including perhaps hay fever and asthma.”
The team found that when mice with eczema made IgE in response to environmental allergens, they began to itch. However, instead of activating mast cells which produced histamine, the IgE activated basophils (a kind of white blood cell), activating a different nerve pathway to normal itching.
The discovery that eczema is exacerbated by allergens may help people avoid severe itching episodes, as well has helping the development of new targets for treatment.
Source: News-Medical.Net
Journal information: Wang, F., et al, A basophil-neuronal axis promotes itch. Cell, 2021 doi.org/10.1016/j.cell.2020.12.033.
