The CD123 protein, also known as the Interleukin-3 receptor subunit alpha (IL-3RA) or CD123, is a crucial component of the interleukin-3 (IL-3) receptor complex and belongs to the Type I cytokine receptor family, specifically the Class 5 subfamily. CD123 serves as the high-affinity receptor for IL-3, forming a heterodimeric receptor complex with the β chain (CSF2RB). This protein mediates the stimulatory effects of IL-3 on the proliferation and differentiation of various hematopoietic cells, including pluripotent hematopoietic stem cells and lineage-committed cells. CD123 is expressed on normal plasmacytoid dendritic cells, basophils, monocytes, and eosinophils, and is overexpressed in various hematologic malignancies. In clinical research, the expression of CD123 is associated with chemotherapy resistance and high-risk genetic alterations in certain leukemias, such as acute myeloid leukemia (AML).