The human cell surface glycoprotein complex (gp 120,200) recognized by monoclonal antibody K20 is a component binding to phytohaemagglutinin on T cells.

Monoclonal antibody K20 recognizes a human glycoprotein complex that is not restricted to haematopoietic lineages but is preferentially expressed on early haematopoietic cells, T cells, and monocytes. This glycoprotein complex is made of a constant 120,000-140,000 Mr subunit noncovalently associated at the cell surface with subunits of higher Mr ranging from 150,000 to 200,000 on different cell types. Internal labelling with [35S]methionine and pulse-chase experiments revealed that in the cell the 120,000 Mr glycoprotein of this complex is also noncovalently associated with a 100,000 Mr glycoprotein, and that both glycoproteins are independently biosynthesized. This glycoprotein complex is shown by immunoprecipitation by lectin plus antilectin antibodies and by sequential immunoprecipitations to be one of the cell surface structures bound by phytohaemagglutinin on the surface of normal T cells.