Leucocyte common antigen family is a group of high molecular weight glycoproteins uniquely expressed on the surface of all leukocytes and their hemopoietic progenitor cells.
Members of this family differ by their protein sequence and carbohydrate structure. Each leukocyte population expresses LCA in a particular pattern. Thymocytes express the lowest molecular weight form, B lymphocytes express the highest molecular weight form. T lymphocytes express a variety of intermediate forms. All in all, LCA are a major constituent of lymphocyte membranes, occupying up to 10% of their surface.