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