Griffonia simplicifolia lectin (GSL I+II) is affinity puritied from a woody climbing shrub native to Africa. It consists of both lectins GSL I+II. GSL I+II shows specificity for blood group B greater than blood group A1. This lectin interacts with pulmonary microvascular endothelial cells, but does not readily interact with pulmonary arterial endothelial cells. This binding pattern has been successfully utilized to enrich cell populations in vitro that possess functional behaviors characteristic of those seen in vivo.Cy5, when bound to Griffonia simplicifolia Lectin (GSL I+II), can show the binding pattern of this lectin in cellular imaging and flow cytometry. The excitation wavelength required for Cy5 to fluoresce is high enough to avoid overlap with most other fluorochromes, making it useful for dual-labeling experiments. Because of this high excitation, there is typically less background from autofluorescence of biological specimens.