Thymic stromal lymphopoietin (TSLP) is a protein belonging to the cytokine family. It is known to play an important role in the maturation of T cell populations through activation of antigen presenting cells.

TSLP is produced mainly by non-hematopoietic cells such as fibroblasts, epithelial cells and different types of stromal or stromal-like cells. These cells are located in regions where TSLP activity is required.

It mainly impacts myeloid cells and induces the release of T cell-attracting chemokines from monocytes[citation needed] and enhances the maturation of myeloid (CD11c+) dendritic cells. TSLP has also been shown to activate the maturation of a specific subset of dendritic cells located within the epidermis, called Langerhans cells. Within the thymus TSLP activation of both myeloid and plasmacytoid (CD123+) dendritic cells results in the production of regulatory T cells. TSLP expression is linked to many disease states including asthma inflammatory arthritis, atopic dermatitis, eczema, eosinophilic esophagitis and other allergic states.[10][11] The factors inducing the activation of TSLP release are not clearly defined.