The SH-3 and SH-4 antibodies recognize distinct epitopes on CD73 from human mesenchymal stem cells

Mesenchymal stem cells (MSCs) are pluripotent cells in the bone marrow that have the capacity to differentiate along a number of connective tissue lin eages, including cartilage, bone, adipose tissue, and stroma. The SH-3 and SH-4 monoclonal antibodies recognize epitopes present on the surface of hum an MSCs. This study describes the isolation and characterization of the ant igen that is recognized by these antibodies. A protein of molecular weight approximately 67 kDa was immunoprecipitated from a solubilized membrane pre paration of human MSCs using the SH-3 antibody. Analysis of peptides derive d from this protein by mass spectrometry and sequencing identified it as CD 73 (ecto-5'-nucleotidase). The SH-4 antibody was also shown to react with p urified bovine CD73 by immunoblotting, but the SH-3 antibody failed to reac t with the bovine protein. These results indicate that both SH-3 and SH-4 e pitopes are present on CD73, but they are distinct. CD73, present in lympho id tissue, plays a role in the activation of B-lymphocytes and in signal tr ansduction in the hematopoietic compartment of bone marrow. The role that C D73 may play in bone marrow stromal interactions and in the differentiation of MSCs is discussed. (C) 2001 Elsevier Science.