外源凝集素(Lectin)是蛋白质,能凝集红细胞、淋巴细胞、肿瘤细胞及精子、细菌、真菌等。在自然界中广泛分布,主要存在于植物的种子里,特别是豆科植物种子里,而在植物的其它部位如根、茎、叶内也同样存在。目前已从1,000多种植物中获得外源凝集素。不仅如此,无脊椎动物(例如蜗牛和马蹄形蟹)以及低等脊椎动物(例如鳗)也都含有此类物质。Stillmark(1888) Lectin is a protein that agglutinates red blood cells, lymphocytes, tumor cells and sperm, bacteria, fungi and the like. Widely distributed in nature, mainly in the seeds of plants, especially leguminous seeds, but also in other parts of the plant roots, stems and leaves also exist. So far, lectins have been obtained from more than 1,000 kinds of plants. Not only that, invertebrates (such as snails and horseshoe crabs), but also lower vertebrates (such as eels) also contain such substances. Stillmark (1888)