Quantitative differences in lipid raft components between murine CD4⁺ and CD8⁺ T cells

Background: Lipid rafts have been shown to play a role in T cell maturation, activation as well as in the formation of immunological synapses in CD4⁺ helper and CD8⁺ cytotoxic T cells. However, the differential expression of lipid raft components between CD4⁺ and CD8⁺ T cells is still poorly defined. To examine this question, we analyzed the expression of GM1 in T cells from young and aged mice as well as the expression of the glycosylphosphatidylinositol (GPI)-linked protein Thy-1 and cholesterol in murine CD4⁺ and CD8⁺ T cell subpopulations. Results: We found that CD4⁺CD8- and CD8⁺CD4^- thymocytes at different stages of maturation display distinct GM1 surface expression. This phenomenon did not change with progressive aging, as these findings were consistent over the lifespan of the mouse. In the periphery, CD8⁺ T cells express significantly higher levels of GM1 than CD4⁺ T cells. In addition, we observed that GM1 levels increase over aging on CD8⁺ T cells but not in CD4⁺ T cells. We also verified that naïve (CD44^lo) and memory (CD44^hi) CD8⁺ T cells as well as naïve and memory CD4⁺ T cells express similar levels of GM1 on their surface. Furthermore, we found that CD8⁺ T cells express higher levels of the GPI-anchored cell surface protein Thy-1 associated with lipid raft domains as compared to CD4⁺ T cells. Finally, we observed higher levels of total cellular cholesterol in CD8⁺ T cells than CD4⁺ T cells. Conclusion: These results demonstrate heterogeneity of lipid raft components between CD4⁺ and CD8⁺ T cells in young and aged mice. Such differences in lipid raft composition may contribute to the differential CD4 and CD8 molecule signaling pathways as well as possibly to the effector responses mediated by these T cell subsets following TCR activation.