Purified human CD4⁺ T lymphocytes demonstrate activation-dependent expression of granzyme B but not granzyme A. (A) Human CD4⁺ T lymphocytes exhibit a differential increase in side scatter (SSC)/granularity and forward scatter (FSC)/size when activated by IL-2, CD3/CD28, or CD3/CD46. (B) Granzyme B expression in human CD4⁺ T cells activated by IL-2, CD3/CD28, or CD3/CD46. (C) Western blot analysis for perforin expression (top panel) in purified human CD4⁺ T lymphocytes activated by IL-2, CD3/CD28, or CD3/CD46. Partially purified perforin is shown as a positive control. The Western blot was reprobed (bottom panel) with an antiactin antibody to assess for protein loading. (D) Representative FACS analysis demonstrating the kinetics of activation and granzyme expression in CD3/CD46-stimulated CD4⁺ T lymphocytes over 6 days. Data shown are representative of 3 or more independent donor samples. Percentages of total cells in each quadrant are indicated in the upper right corner of each subpanel in panels B and D.