Since the 1880’s, it has been known that extracts from certain plants could agglutinate red blood cells. In the 1940’s, agglutinins were discovered which could “select” types of cells based on their blood group activities.
Although “lectin” was originally coined to define agglutinins that could discriminate among types of red blood cells, today the term is used more generally and includes sugar-binding proteins from many sources regardless of their ability to agglutinate cells.
Lectins have been found in plants, viruses, microorganisms, and animals but despite their ubiquity, in many cases their biological function is unclear.