The 30-F1 monoclonal antibody specifically recognizes CD24 which is also known as Heat-Stable Antigen (HSA or HsAg). CD24 is a highly glycosylated sialoprotein that is glycosylphosphatidylinositol (GPI)-linked to the cell membrane. CD24 is encoded by Cd24a (CD24a antigen) and is variably expressed on thymocytes, lymphocytes, monocytes, granulocytes, and erythrocytes. Hematopoietic stem cells of the embryonic yolk sac and fetal liver express CD24. The expressed levels of CD24 vary during the developmental stages of cells within the T and B cell lineages. In the bone marrow, hematopoietic progenitors acquire CD24 expression upon commitment to the lymphocyte lineage. Immature B cells in the bone marrow and spleen of adult mice express high levels of CD24, whereas mature peripheral B cells express intermediate levels of CD24. The majority of thymocytes express high levels of CD24, whereas mature thymic and peripheral T cells do not express CD24. In contrast, γδ TCR-bearing thymocytes which emigrate to the spleen are CD24+. Dendritic cells of the thymus, spleen, and liver and epidermal Langerhans cells reportedly express CD24 whereas NK cells and plasma cells do not. CD24 can function as an adhesion molecule and serve as a ligand for CD62P (P-selectin). It can be involved in the costimulation of CD4+ T cells by B cells as well as function as a "co-inducer" of in vitro thymocyte maturation. 30-F1 and other CD24-specific monoclonal antibodies, such as, M1/69 and J11d, can show subtle differences in the staining patterns for different lymphocyte populations. For this reason, the consistent use of the same CD24-specific antibody is recommended during research studies.