Lipopolysaccharide-Elicited TSLPR Expression Enriches a Functionally Discrete Subset of Human CD14⁺ CD1c⁺ Monocytes

Thymic stromal lymphopoietin (TSLP) is a cytokine produced mainly by epithelial cells in response to inflammatory or microbial stimuli and binds to the TSLP receptor (TSLPR) complex, a heterodimer composed of TSLPR and IL-7 receptor α (CD127). TSLP activates multiple immune cell subsets expressing the TSLPR complex and plays a role in several models of disease. Although human monocytes express TSLPR and CD127 mRNAs in response to the TLR4 agonist LPS, their responsiveness to TSLP is poorly defined. We demonstrate that TSLP enhances human CD14⁺ monocyte CCL17 production in response to LPS and IL-4. Surprisingly, only a subset of CD14⁺ CD16^- monocytes, TSLPR⁺ monocytes (TSLPR⁺ mono), expresses TSLPR complex upon LPS stimulation in an NF-κB- and p38-dependent manner. Phenotypic, functional, and transcriptomic analysis revealed specific features of TSLPR⁺ mono, including higher CCL17 and IL-10 production and increased expression of genes with important immune functions (i.e., GAS6, ALOX15B, FCGR2B, LAIR1). Strikingly, TSLPR⁺ mono express higher levels of the dendritic cell marker CD1c. This evidence led us to identify a subset of peripheral blood CD14⁺ CD1c⁺ cells that expresses the highest levels of TSLPR upon LPS stimulation. The translational relevance of these findings is highlighted by the higher expression of TSLPR and CD127 mRNAs in monocytes isolated from patients with Gram-negative sepsis compared with healthy control subjects. Our results emphasize a phenotypic and functional heterogeneity in an apparently homogeneous population of human CD14⁺ CD16^- monocytes and prompt further ontogenetic and functional analysis of CD14⁺ CD1c⁺ and LPS-activated CD14⁺ CD1c⁺ TSLPR⁺ mono.