Many of us are familiar with the itchiness that can accompany an allergic response, along with the urge to scratch when we know we shouldn’t. Scientists are now one step closer to understanding what triggers such allergic responses.

Dendritic cells (DCs) are white blood cells that patrol the body on the look-out for foreign antigens that might pose a threat. Upon detecting a potential threat — sometimes a harmless allergen — certain DCs in the skin can become activated and migrate to the lymph nodes where they interact with T cells in order to initiate an allergic immune response. 

DCs can detect potential invaders using receptors on their surface. However, in a paper recently published in Immunity, researchers from Massachusetts General Hospital and Harvard Medical School found that allergy-initiating DCs isolated from mice did not become activated in response to model allergens, suggesting there must be other factors required for their activation and subsequent migration in living systems.  

Suspecting that the culprit was sensory neurons in close proximity to these DCs in the skin, the researchers injected mice with a chemical that blocks the function of sensory neurons and found that it prevented an allergic response. Furthermore, they showed that certain sensory neurons release a neuropeptide called Substance P in response to allergens. And when Substance P was injected into mice, it caused DCs to move to their lymph nodes, leading to an allergic response. 

Not only does this finding highlight the importance of looking at immune responses both in isolation and within living organisms, the discovery of the role of sensory neurons and Substance P in allergic responses identifies a potential target for allergy medications.