Lectins are proteins or glycoproteins of non-immune origin that agglutinate cells and/or precipitate complex carbohydrates. Lectins are capable of binding glycoproteins even in presence of various detergents. The agglutination activity of these highly specific carbohydrate-binding molecules is usually inhibited by a simple monosaccharide, but for some lectins, di, tri, and even polysaccharides are required. Lectins are isolated from a wide variety of natural sources, including seeds, plant roots and bark, fungi, bacteria, seaweed and sponges, mollusks, fish eggs, body fluids of invertebrates and lower vertebrates, and from mammalian cell membranes. The precise physiological role of lectins in nature is still unknown, but they have proved to be very valuable in a wide variety of applications in vitro, including:

1. Blood grouping and erythrocyte agglutination studies.

2. Mitogenic stimulation of lymphocytes.

3. Lymphocyte subpopulation studies.

4. Fractionation of cells and other particles.

5. Histochemical studies of normal and pathological conditions.

Lens culinaris agglutinin (LCA) occurs in two forms designated LCA60 and LCA120 according to their mol. wt. of approx. 60,000 and 120,000 respectively. Neither LCA60 nor LCA120 is blood group specific. LCA60, also referred to as LCAII, Ricin D or RCL III is extremely toxic, inhibits protein synthesis and has an affinity for N-acetyl-D-galactosamine. LCA120, also referred to as LCAI or RCL (I + II), is an agglutinin and has an affinity for terminal β-D-galactosyl residues. Conjugates are prepared from affinity purified agglutinin LCA120.