CD4+ T cell proliferation response of HCV-immunized mice. The splenocytes were stained with CFSE dye and incubated with different stimulants for 4 days. Cells were stained for surface markers using anti-CD3+ and CD4+-antibodies and tested using flow cytometry. (A) Unstimulated cells showing no proliferation, (B) CE1E2 protein-stimulated cells showing proliferation of the cells which is indicated by the shift of fluoresecence in the cell population (circle), (C) Core peptide stimulated cells showing proliferation. Daughter cells contain half the fluorescent intensity of the parent cell.