Behind the Itch

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In the human body, the sensory nervous system plays a key role in detecting and reacting to allergens, which can lead to itchiness or even hives.

Now, scientists are closer to understanding why.

In a new paper, researchers led by allergy and immunology specialists at Massachusetts General Hospital identified the pathway by which immune and nerve cells interact to cause itching in response to allergens such as pollen, dust mites and mosquito bites.

The paper’s senior author Caroline Sokol and her colleagues found that a poorly understood type of immune cell, known as GD3, plays a big role in allergic reactions. These cells produce a molecule called IL-3 which makes sensory neurons more responsive to allergens in the skin.

IL-3 makes sensory neurons more sensitive to allergens, making them react more easily without directly causing the itch. This happens through a signaling process that triggers the production of certain molecules, which then starts the allergic immune response.

“These weird, very ancient but funny cell types make it absolutely essential for this mosquito-induced itch,” Sokol told Popular Science. “It’s also essential for the downstream allergic immune response to it.”

In a series of experiments, the team found that the removal of IL-3 molecules or GD3 cells in mice, as well as blocking the signaling pathway, made the animals more resistant to itchiness and immune-activating ability of certain allergens.

“By establishing a pathway that controls allergen responsiveness, we have identified a new cellular and molecular circuit that can be targeted to treat and prevent allergic responses including itching,” explained Sokol in a statement.

The number of GD3 cells and their activity appear to be age-dependent, the authors noted. They are now planning to investigate why some people develop more severe allergic reactions than others.

“Allergies are increasing in number, and it’s not just that we’re better at diagnosing them,” Sokol emphasized. “We really need to get to the bottom of why, and there are a lot of questions, but that’s what makes it a fun area of science and medicine to be in.”