BACKGROUND: The IRE1a-XBP1 pathway is a conserved adaptive mediator of the 
unfolded protein response. The pathway is indispensable for the development of 
secretory cells by facilitating protein folding and enhancing secretory 
capacity. In the immune system, it is known to function in dendritic cells, 
plasma cells, and eosinophil development and differentiation, while its role in 
T helper cell is unexplored. Here, we investigated the role of the IRE1a-XBP1 
pathway in regulating activation and differentiation of type-2 T helper cell 
(Th2), a major T helper cell type involved in allergy, asthma, helminth 
infection, pregnancy, and tumor immunosuppression.
METHODS: We perturbed the IRE1a-XBP1 pathway and interrogated its role in Th2 
cell differentiation. We performed genome-wide transcriptomic analysis of 
differential gene expression to reveal IRE1a-XBP1 pathway-regulated genes and 
predict their biological role. To identify direct target genes of XBP1 and 
define XBP1's regulatory network, we performed XBP1 ChIPmentation (ChIP-seq). We 
validated our predictions by flow cytometry, ELISA, and qPCR. We also used a 
fluorescent ubiquitin cell cycle indicator mouse to demonstrate the role of XBP1 
in the cell cycle.
RESULTS: We show that Th2 lymphocytes induce the IRE1a-XBP1 pathway during in 
vitro and in vivo activation. Genome-wide transcriptomic analysis of 
differential gene expression by perturbing the IRE1a-XBP1 pathway reveals 
XBP1-controlled genes and biological pathways. Performing XBP1 ChIPmentation 
(ChIP-seq) and integrating with transcriptomic data, we identify XBP1-controlled 
direct target genes and its transcriptional regulatory network. We observed that 
the IRE1a-XBP1 pathway controls cytokine secretion and the expression of two Th2 
signature cytokines, IL13 and IL5. We also discovered that the IRE1a-XBP1 
pathway facilitates activation-dependent Th2 cell proliferation by facilitating 
cell cycle progression through S and G2/M phase.
CONCLUSIONS: We confirm and detail the critical role of the IRE1a-XBP1 pathway 
during Th2 lymphocyte activation in regulating cytokine expression, secretion, 
and cell proliferation. Our high-quality genome-wide XBP1 ChIP and gene 
expression data provide a rich resource for investigating XBP1-regulated genes. 
We provide a browsable online database available at http://data.teichlab.org .