Characterization of dendritic cell subsets and novel basophil progenitors involved in type 2 immune responses

Abstract

PART I Dendritic cells (DCs) play a critical role in directing immune responses. Previous studies have identified a variety of DC subsets and elucidated their context-dependent functions that parallel those of effector T helper (Th) cell subsets. However, little is known about DC subsets responsible for differentiation of Th2 cells governing allergic contact dermatitis. Here, I sought to determine the DC subset(s) that mediate Th2 priming in hapten-sensitized mice. I induced hapten-specific Th2 differentiation by sensitizing the mice with single application of fluorescein isothiocyanate (FITC) dissolved in acetone:dibutyl phthalate, and traced immune cells responsible for inducing Th2 differentiation process at the primary stimulation by using the mice enabling me to track Th2 priming in vivo and to delete basophils and specific DC subsets. My analysis revealed that IL-4 was produced in vivo as early as day 3 from CD4+ T cells with a single application of FITC. Basophils, despite producing IL-4 one day earlier than T cells, were found to be dispensable for Th2 differentiation. Instead, I demonstrated that $CD326^+$ dermal DCs and LCs were redundantly required for FITC-induced Th2 differentiation in vivo. Moreover, the cooperation of $CD326^+$ LCs and $CD11b^+$ DCs differentiated naive T cells into Th2 cells in vitro. Collectively, my findings highlight at least two DC subsets that play a critical role in polarizing na？ve $CD4^+$ T cells to Th2 cells and support a “two-hit” model for Th2 differentiation.

PART II Basophil is a least abundant granulocyte. It was considered as redundant population which mimics mast cells. Accumulating reports now consider basophils as important mediators in various allergic and helminth infection models. However, studies on basophil development are limited due to lack of studies on basophil progenitors and development. I introduce two novel basophil progenitors, characterized by $lineage^-ckit^-CD200R3^-MAR1^+$ and $lineage^-ckit^-CD200R3^+MAR1hi$. I demonstrated the differentiation of these progenitors into mature basophils both in vitro and in vivo. By administrating IL-3, I observed dramatic expansion of basophil progenitors. Importantly, the cytokine producing potential in basophil progenitors were greater than mature basophil and the cytokines required for optimal production of IL-4 and IL-13 by basophil progenitors were different. IL-3 was sufficient for optimal IL-4 production whereas IL-25, IL-33 and TSLP were needed for optimal IL-13 production. This findings will facilitate the current understanding of basophil progenitors and pathological roles in number of allergic diseases.