A new study by immunologists and allergists at Massachusetts General Hospital and Harvard Medical School found specific immune-system features that may decide whether a mosquito bite itches.
What Did the Scientists Discover?
The researchers focused on the immune differences between individuals who experience intense itching from mosquito bites and those who do not.
The skin is full of sensory neurons—nerve cells that detect environmental changes and trigger sensations like pain or itch. When someone encounters an allergen like mosquito saliva, those neurons can respond by causing an itch. They also help activate nearby immune cells, which start an inflammatory response that produces swelling and redness.
With frequent allergen exposure, some people develop chronic allergic inflammation. That changes the affected tissues: immune cells that react to allergens can alter nerve sensitivity, making nerves more or less likely to respond to the allergen.
“Everyone has sensory neurons, so we can all feel itchiness, but not everyone develops allergies, even though we are surrounded by the same allergens,” said Professor Caroline Sokol, the study’s lead author. She and her colleagues wanted to know what makes some people’s sensory neurons activate in response to allergens and others’ not.
To investigate this, the researchers exposed laboratory mice to a chemical called papain, which induces itching and causes the rodents to scratch their skin. Different groups of mice lacked various immune cells. The study found that mice lacking a specific type of T-cell did not scratch when exposed to papain.
Professor Sokol’s team aimed to understand how these cells, known as GD3, controlled sensory nerve responses. The scientists cultured GD3 cells in the lab and treated them with a chemical that caused them to release signaling molecules called cytokines. They then injected mice that had normal immune systems with a solution containing the cytokine produced by the cultured cells.
These manipulations didn’t directly cause itching, but they enhanced the scratching responses of the rodents to various allergens, including mosquito saliva. This suggests that something released by GD3 cells amplified the itchiness triggered by the nerves.
By comparing chemicals secreted by GD3 cells with those from other immune cells in the skin’s central layer, the team found a single unique factor from GD3: interleukin 3 (IL-3), a cytokine that helps regulate inflammation. Only certain sensory neurons responded to IL-3, and those neurons were the ones prone to causing itch. That suggests the cytokine primes the neurons to react to allergens.
The results of the study were published in the journal Nature.
