A review of recently published work is presented on the nature of the agglutination of human peripheral lymphocytes and cultured lymphoblastoid cells by the hemolymph agglutinins of two arachnoids, the Horsefoot (Limulus polyphemus), alias Horseshoe Crab, and the Saharan Scorpion (Androctonus australis). Microagglutination techniques were utilized to study the specificity of the whole serum and purified agglutinin(s) of Limulus and the whole serum agglutinin(s) of Androctonus. Peripheral human

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... ymphocytes of patients with chronic lymphocytic leukemia (CLL) gave higher agglutination titers and scores than did normal cells, with both species of invertebrate agglutinins. However, human B cells gave higher, although overlapping degrees of agglutination, than T cells. The major cell membrane receptor site for agglutinins of both species was the sialic acid moiety, N-acetyl neuraminic acid. Selected literature on plant and invertebrate agglutinins (lectins) was reviewed. These lectins are underscored as valuable cell membrane probes of surface receptors of human lymphocyte subpopulations.