TSLP is a hemopoietic protein that was initially identified from mouse thymic stromal cell line that promoted the development of B cells. TSLP overlaps biological activities with IL-7 and can co-stimulate growth of thymocytes and mature T cells alongside supporting lymphopoiesis. Human TSLP shares approximately 43% amino acid sequence identity with mouse TSLP. Human TSLP has been detected in many tissues although the highest level of expression has been found in the heart, liver, testis and prostate. TSLP signals through a heterodimeric receptor complex that consists of IL-7R-alpha and the TSLP-R.