Immunocytochemical localization of CDw60 antigens on human peripheral T cells

About 25-35% of human T cells display the CDw60 ganglioside (9-O-acetyl-GD3 ) antigen at the cell surface [E.P. Rieber, in W. Knapp, B. Dorken, W.R. Gi lks, E.P. Rieber, R.E. Schmidt, H. Stein, A.E.G.K. von dem Borne (Eds.), Le ucocyte Typing IV, Oxford University, Oxford, 1989, p. 361.]. Other leucocy tes do not express this antigen on the cell surface. This led us to investi gate its presence by flow cytometry and immunoelectron microscopy (IEM). Fl ow cytometric analysis of isolated peripheral T cells showed 26% of the cel l population to have the CDw60 antigen expressed on the cell surface wherea s 74% did not. Similarly, IEM analysis of 262 random T cells by the preembe dding immunogold labeling technique revealed CDw60 surface expression to be tetrapartite: (a) the majority of 63.7% of the T cells did not show any su rface associated gold label; (b) 19.5% were of low CDw60 surface exposition , corresponding to a linear density of 0.05-2.0 gold markers per mum; (c) a bout 13.4% showed a medium surface exposition with a linear density of 2.1- 4.5 gold markers per mum; and (d) a high exposition, ranging from 4.6 to 9. 0 gold markers per mum, was seen at 3.4% of the T cells. From postembedding label experiments, which additionally make access to the antigen localized within the cytoplasm, it was found that nearly all T cells contained low l evels of intracellular CDw60. Most of it was found to be associated with th e cytoplasmic membrane or vesicles, derived from the Golgi. Immunogold conj ugates associated with the cytoplasmic membrane showed a linear density up to 0.6 gold markers per mum. The asymmetric expression of the CDw60 antigen on human T cells and its occurrence in nearly all T cells suggests that it s surface presentation is tightly regulated. (C) 2000 Elsevier Science Ltd. All rights reserved.