A new study conducted by immunologists and allergists at Massachusetts General Hospital and Harvard Medical School has uncovered specific features in immune system activity that may determine whether a mosquito bite will ultimately itch.
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 densely populated with sensory neurons, which are nerve cells that detect changes in the environment and trigger sensations such as pain or itching in response. When a person encounters a potential allergen, like mosquito saliva, these neurons detect it and can respond with itching. They also help activate nearby immune cells that initiate an inflammatory response, resulting in swelling and redness.
In some individuals who are frequently exposed to allergens, chronic allergic inflammation can develop. This fundamentally alters the tissues where it occurs, as reported by Live Science. For instance, immune cells that react to allergens can change the sensitivity of nerves, making them more or less likely to respond to the substance.
“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 lead author of the study. “So what exactly determines whose sensory neurons activate in response to allergens and whose do not?” pondered the researcher and her colleagues.
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 were missing 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 with a normal immune system with a solution containing the cytokine produced by the cultured cells.
These manipulations did not 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 the chemicals secreted by GD3 cells with those from other immune cells in the central layer of the skin, the researchers discovered that only one factor was unique to GD3 cells: interleukin 3 (IL-3), which is known to help regulate inflammation. Only certain sensory neurons responded to IL-3, and those that did were prone to causing itchiness. This indicates that the cytokine “prepares” the neurons to react to allergens.
The results of the study were published in the journal Nature.