Immunoelectron microscopy of T cell receptors and membrane lipids

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High-affinity antigen receptor on T cells consists of ligand-binding α and β chains and signaling chains, γ, δ, ε and ζ chains. Cross-linking by multivalent antigen results in the aggregation of the bound IgG/α or β chain complexes at the cell surface, triggering cell activation, and subsequent internalization through coated pits. However, the precise topographical alterations of the signaling chains during stimulation remain unclarified despite their importance in ligand-binding/signaling coupling. We examined the distribution of T cell antigen receptor and membrane lipid, sphingomyelin, during stimulation as revealed by immunogold electron microscopy. Immunolocalization of γ, δ, ε and ζ chains was homogeneously distributed on the cell surfaces before stimulation, while cross-linking with multivalent antigen, caused a distinct aggregation of these signaling chains on the cell membrane. Moreover, ζ chain was localized on the sphingomyelin-rich membrane areas. These findings show new aspects toward the investigation of transmembrane signaling of T cell response.