Lectins are a special group of proteins that bind to specific carbohydrate groups on cell walls or membranes. They were first described in 1888 and were named for the ability possessed by some of the proteins to agglutinate red blood cells belonging to certain human blood groups selectively. Lectins are still often utilized for this purpose, but are also widely used in laboratories to isolate glycoproteins for observation and study. Many lectins are derived from the seeds of leguminous plants, but a number of other sources for the proteins have also been identified. The proteins are often subdivided into an array of subcategories, such as galectins, collectins, and annexins, based on shared characteristics.

The culture of rat enteroglial cells illustrated above was labeled with Texas Red conjugated to wheat germ agglutinin, a lectin that selectively binds with sialic acid residues. The culture was subsequently labeled for the cytoskeletal F-actin network with Alexa Fluor 488, and for DNA in the cell nucleus with the ultraviolet-absorbing probe DAPI. Images were recorded in grayscale with a QImaging Retiga Fast-EXi camera system coupled to an Olympus BX-51 microscope equipped with bandpass emission fluorescence filter optical blocks provided by Omega Optical. During the processing stage, individual image channels were pseudocolored with RGB values corresponding to each of the fluorophore emission spectral profiles.