EdU incorporation is an alternative non-radioactive assay to [(3)H]thymidine uptake for in vitro measurement of mice T-cell proliferations.

Rationale: T lymphocyte proliferations can be measured by [(3)H]thymidine incorporation. However, many labs avoid this technique because of the need to use radioactive substrates. In addition, [(3)H]thymidine incorporation method does not permit simultaneous characterization of the proliferating cells. We developed the 5-ethynyl-2'-deoxyuridine (EdU) and Cu(I)-catalyzed cycloaddition "click" reaction assay to measure T-cell responses by flow cytometry.

Methods: Spleen cells from normal, immune-deficient purine nucleoside phosphorylase (PNP) defective (PNP-/-) mice or PNP-/- mice with partial immune reconstitution were stimulated with anti-CD3 antibodies. The correlation (r) between [(3)H]thymidine and EdU incorporations into stimulated T cells was measured and the stimulation index (SI), the ratio between stimulated and non-stimulated cells, was calculated. Flow cytometry was used to characterize the proliferating cells.

Results: EdU and [(3)H]thymidine incorporation into normal spleen cells were strongly correlated (r=0.89). Following stimulation, EdU incorporation into spleen cells from normal and immune-reconstituted PNP-/- mice was significantly increased compared to PNP-/- immune-deficient mice. Immune-deficient PNP-/- mice had increased [(3)H]thymidine and EdU incorporation into non-stimulated spleen cells, indicative of spontaneous proliferation. Analysis of EdU incorporation showed that the increased proliferation was due primarily to cells expressing CD3, CD4 and IgM.

Conclusion: EdU-Click technology accurately measures proliferation of murine T lymphocyte and can be used as an alternative to [(3)H]thymidine assays. The EdU-Click technology also allows identification of proliferating cells.