However, although the role of the IL-33/ST2 axis in Th2/IL-31 and Th17 immune responses, characterizing the development of allergic respiratory diseases, has been recently clarified [38,39], the relationship between IL-31 and IL-33 in osteoporosis is quite peculiar and the data from the literature are often contradictory. This evidence concerns the gene IL33 and osteoporosis.