ABSTRACT
Human CRTh2(+) Th2 cells express IL-25 receptor (IL-25R) and IL-25 has been shown to potentiate production of Th2 cytokines. However, regulation of IL-25R and whether it participates in Th2 differentiation of human cells have not been examined. We sought to characterize IL-25R expression on CD4(+) T cells and determine whether IL-25 plays a role in Th2 differentiation. Naïve human CD4(+) T cells were activated in the presence of IL-25, IL-4 (Th2 conditions) or both cytokines to assess their relative influence on Th2 differentiation. For experiments with differentiated Th2 cells, CRTh2-expressing cells were isolated from differentiating cultures. IL-25R, GATA3, CRTh2 and Th2 cytokine expression were assessed by flow cytometry, qRT-PCR and ELISA. Expression of surface IL-25R was induced early during Th2 differentiation (2 days). Addition of IL-25 to naïve CD4(+) T cells revealed that it induces expression of its own receptor, more strongly than IL-4. IL-25 also increased the proportions of IL-4-, GATA3- and CRTh2-expressing cells and expression of IL-5 and IL-13. Activation of differentiated CRTh2(+) Th2 cells through the TCR or by CRTh2 agonist increased surface expression of IL-25R, though re-expression of CRTh2 following TCR downregulation was impeded by IL-25. These data suggest that IL-25 may play various roles in Th2 mediated immunity. We establish here it regulates expression of its own receptor and can initiate Th2 differentiation, though not as strongly as IL-4.
ABSTRACT
PGD2 has long been implicated in allergic diseases. Recent cloning of a second PGD2 receptor, DP2 (also known as CRTh2), led to a greater understanding of the physiological and pathophysiological implications of PGD2. PGD2 signaling through DP1 and DP2 mediates different and often opposite effects in many cell types of the immune system. Although mast cells (MC) are the largest source of PGD2 in the body, there is little information about their potential expression of DP2 and its functional significance. In this study, we show that tissue MC in human nasal polyps express DP2 protein, and that human MC lines and primary cultured human MC express mRNA as well as protein of DP2. By immunohistochemistry, we detected that 34% of MC in human nasal polyps expressed DP2. In addition, flow cytometry showed that 87% of the LAD2 human MC line and 98% of primary cultured human MC contained intracellular DP2. However, we could not detect surface expression of DP2 on human MC by single cell analysis using imaging flow cytometry. Blocking of endogenous PGD2 production with aspirin did not induce surface expression of DP2 in human MC. Two DP2 selective agonists, DK-PGD2 and 15R-15-methyl PGD2 induced dose-dependent intracellular calcium mobilization that was abrogated by pertussis toxin, but not by three DP2 selective antagonists. MC mediator release including degranulation was not affected by DP2 selective agonists. Thus, human MC express DP2 intracellularly rather than on their surface, and the function of DP2 in human MC is different than in other immune cells such as Th2 cells, eosinophils and basophils where it is expressed on the cell surface and induces Th2 cytokine and/or granule associated mediator release. Further studies to elucidate the role of intracellular DP2 in human MC may expand our understanding of this molecule and provide novel therapeutic opportunities.
