HUMAN LYMPHOCYTE-ACTIVATION IS ASSOCIATED WITH THE EARLY AND HIGH-LEVEL EXPRESSION OF THE ENDOGENOUS LECTIN CSL AT THE CELL-SURFACE

Lymphocytes undergo activation in response to antigens, cytokines, lec tins and antibodies interacting with specific cell-surface molecules o r through substances influencing signal transduction pathways. This st udy shows that human T- and B-cells stimulated using phorbol eaters or plant lectins express early (2 h using phorbol esters and 24 h using plant lectins) a high level of a polyvalent carbohydrate-binding prote in, the cerebellar soluble lectin (CSL), which is in part externalized . The lectin, immunologically related to CDw70, interacts with specifi c glycoprotein ligands of the lymphocyte surface, including CD3 on T-c ells and CD24 on B-cells. Major changes in phosphorylations associated with activation appear as largely CSL-dependent since they are specif ically inhibited by anti-CSL Fab fragments. It is suggested that the l ectin induces the clustering of specific cell-surface glycoproteins an d plays the role of an endogenous amplifier of activation signals.