Description: The AA4.1 monoclonal antibody reacts with mouse C1qRp, an approximately 130-140 kDa C-type lectin-like type I transmembrane protein. The AA4.1 antigen was originally identified as an antigen expressed on early stages of B cell development in bone marrow. Adult spleen and fetal liver also have detectable numbers of AA4.1 positive cells. In combination with other markers of hematopoietic progenitor cells such as Thy-1, Sca-1, c-Kit, CD43, and CD24, the bone marrow Lymphoid-Committed Progenitors (CLP) can be segregated into more primitive and more differentiated subsets based on expression of AA4.1. Correlated expression of surface IgM (sIgM), CD23, and AA4.1 antigen has also been used to define three nonproliferative subpopulations of immature/transitional peripheral B cells designated: T1 (AA4.1+/CD23-/sIgMhi), T2 (AA4.1+/CD23+/sIgMhi), and T3 (AA4.1+/CD23+/sIgMlo). AA4.1 is also reported to be expressed in cytoplasmic vesicles in endothelial cells, megakaryoblasts, and platelets. It is reported that monoclonal antibodies AA4.1 and 493 recognize different epitopes of the same molecule.
