Differentiation of innate type-2 effector cells.

Type-2 immune responses are the underlying cause of many allergic diseases and provide protection against parasitic infection. Effective type-2 immune responses are generated by type-2 helper CD4(+) T cells (Th2) as well as type-2 innate effector cells. While we have learned a great deal about how CD4(+) Th2 cells regulate their Th2 cytokine gene transcription, we still do not know how type-2 innate effector cells acquire their capacity to express Th2 cytokine genes. Furthermore, it remains poorly understood how Th2 cytokines regulate the differentiation of innate type-2 progenitor cells. In this review, we will focus on (1) the long distance interaction between the sites of allergic inflammation and the site of hematopoiesis in the bone marrow, (2) the characteristics of innate type-2 progenitors, and (3) the molecular mechanisms by which innate type-2 effector cells acquire the capacity to produce type-2 cytokines.