The role of basophils in allergic inflammation

In recent years there has been growing evidence to suggest a major role for basophils in allergy despite being one of the rarest leukocytes. These blood-borne cells have clearly been observed to invade other tissues such as skin or lung affected by allergic inflammation. More recent studies have shown that basophil responses — typified by degranulation — correlate with the severity of allergic reactions in food allergy. However, despite studies suggesting major input in governing allergy symptoms their immunomodulatory roles are less clearly defined. While basophils are an important early source for pro-allergic Th2-type cytokines, interleukins 4 and 13 (IL-4 and IL-13), it is unclear whether they play a role in initiating allergic immunity or merely enhance existing allergy. In this regard, mouse models of allergy are more supportive of a key innate immune function of basophils in orchestrating Th2-type immunity and allergy, and potentially acting as antigen presenting cells. However, these important roles have not been observed in primary human basophils although there is clear evidence to suggest that they crucially promote group 2 innate lymphoid cells (ILC2s) in atopic dermatitis. Shedding more light on these immunomodulatory roles of human basophils, and differentiating them from their rodent counterparts, will provide much needed greater understanding of this elusive cell type, especially in view of developing new therapeutic strategies against allergy.