Le(X) and related structures as adhesion molecules.

Le(x) (alpha 1-->3 fucosylated type 2 chain) functions as an adhesion molecule capable of Ca(2+)-mediated homotypic binding. Cells with high surface expression of Le(x) therefore exhibit strong self-aggregation (based on Le(x)-Le(x) interaction) in the presence of Ca2+. In this review, I have summarized several lines of supporting data for this concept, and the role of Le(x)-Le(x) interaction in the process of embryo compaction and autoaggregation of F9 teratocarcinoma cells. In general, cell adhesion events based on Le(x)-Le(x) interaction may be followed and reinforced by integrin- or Ig receptor-based adhesion systems. SLe(x), the 2-->3 sialosyl derivative of Le(x), and its positional isomer SLe(a), have been identified as the target molecules for selectin-dependent cell adhesion. Adhesion of leukocytes or tumour cells to ECs or platelets, which express E-selectin and P-selectin respectively, is initiated by this process. The target epitopes SLe(x) and SLe(a) are presented mainly on transmembrane glycoproteins having many clusters of O-linked carbohydrate chains. Therefore, inhibition of O-glycosylation may be effective for blocking selectin-mediated cell adhesion. The abundant presence of Le(x) epitope in the central nervous system, and the physiological changes of Le(x) expression as described in this monograph, reflect the adhesive properties of this molecule and its sialyosylated and/or fucosylated derivatives.