Fluoresceinated alpha 2-macroglofilen as a probe for studying macrophages

The potential value of fluorescein-conjugated human α2-macroglobulin as a probe for studying macrophages in murine peritoneal exudate and spleen cell suspensions has been investigated using a fluorescence-activated cell sorter. These studies revealed that the number of α2-macroglobulin-positive cells in the mixtures examined correlated closely with their macrophage content as determined morphologically. Furthermore cells separated on the FACS on the basis of their strong α2-macroglobulin binding exhibited macrophage morphology and expressed Fc receptors on their surface. Conversely the α2-macroglobulin-negative population contained few macrophages or Fc rosette-forming cells. Extensive blocking and comparative binding studies with a number of purified human α2-macroglobulin preparations and derivatives thereof, and a variety of purified proteins, confirmed that the binding of fluorescein-conjugated α2-macroglobulin to peritoneal exudate cells was specific. Furthermore the binding occurs in a highly reproducible manner. These observations suggest that fluorescein-conjugated α2-macroglobulin in conjugation with flow cytometry is a sensitive and reliable method for both identifying and isolating subpopulations of macrophages.