EVIDENCE FOR THE EXISTENCE OF GANGLIOSIDE-ENRICHED PLASMA-MEMBRANE DOMAINS IN HUMAN PERIPHERAL LYMPHOCYTES

In human peripheral blood lymphocytes (PBL) monosialoganglioside GM3 a ppears to be the major ganglioside on the cell plasma membrane. We hav e analyzed the expression and distribution pattern of GM3 molecules on the lymphocyte plasma membrane by flow cytometry, immunofluorescence, and immunoelectron microscopy, using an anti-GM3 monoclonal antibody. Both CD4+ and CD8+ T lymphocyte subpopulations showed substantial GM3 expression, as determined by thin-layer chromatography and flow cytom etric analysis. A clustered distribution of GM3 molecules on the cell surface, revealed by immunofluorescence and immunogold electron micros copy, clearly indicated the presence of GM3 molecule-enriched plasma m embrane domains. To better define these domains, we analyzed the gangl ioside and protein composition of buoyant low-density Triton-insoluble (LDTI) lymphocyte fractions. The results show that GM3 is enriched si milar to 20-fold in LDTI fraction, as compared with total cell lysates . In addition, CD4 and lck molecules are selectively recovered in the same LDTI fraction isolated from human PBL. These findings, together w ith the observation that anti-CD4 co-immunoprecipitated GM3, support t he hypothesis of a possible GM3-CD4 interaction and suggest a role for gangliosides as structural components of the membrane multimolecular signaling complex involved in T-cell activation, antigen recognition, and other dynamic lymphocytic plasma membrane functions.