In order for allergy to exist, allergen sensitisation must first occur. Antigen-presenting cells, including macrophages and dendritic cells are responsible for detecting the allergen. This can occur in a variety of ways, including inhalation into the nose and lungs, as well as through the skin and the gastrointestinal tract. When cells containing an antigen interact with an allergen, there is perceived to be an invader, even though this substance is not believed to be harmful on a normal basis. Subsequently, the allergen is then absorbed into the antigen-presenting cell, processed and then displayed on the surface of the cell.
What happens next is that the cell then migrates and presents the allergen, this process stimulates the B-cell, and produces antibodies specific to the allergen. From here, these specific antibodies, (IgE) are then released and are able to attach themselves to receptors on various surfaces of other cells in the mucosal surfaces and on subsequent basophils contained within the blood.
There is a period of sensitisation, and afterwards comes a period of latency, then on subsequent re-exposure to the allergen the allergic response is triggered. In this process an allergen is able to connect with the IgE on the surfaces of the mast cell, and this causes the cell to release nasty and inflammatory cell mediators. These include histamine and other mediators, all of which act differently and cause a variety of symptoms in different organs.
In order to fully define allergy pathogenesis and develop novel therapeutic possibilities, the key may well be in further understanding the gut microbiome and advancing research into epigenetics.
Prince, B.T; Mandel, M.J; Nadeau, K; Singh, A.M. Gut Microbiome and the Development of Food Allergy and Allergic Disease. Pediatric Clinics of North America. 2015;62:1479-92 Xie, J; Lotoski L.C; Chooniedass, R; et al. Elevated antigen-driven IL-9 responses are prominent in peanut allergic humans. PLoS One. 2012;7(10):e45377 Nursing Times. (2006). The pathophysiology of allergic responses.