Post-activation NK cells have reduced cytolytic activity.

<p>A. Post-activation CD25⁺ and non-activated CD25⁻ NK cells were isolated from spleens of B16-bearing mice and were incubated immediately with activating antibodies against NKG2D or NKp46 in the presence of anti-CD107 antibody to detect degranulation. While the degranulation had to be induced in CD25⁻ NK cells by the activating antibodies (top row), CD25⁺ NK cells degranulated spontaneously. B. Post-activation CD25⁺ NK cells isolated from spleens of B16-bearing mice and control NK cells isolated from normal spleens were expanded for 7 days in IL-2 in vitro. Western analyses (top) using three independent isolations each revealed reduced protein levels of granzyme B and perforin but similar levels of β-actin in post-activation NK cells. Intracellular cytometry analyses (bottom) of NK1.1⁺ cells showed that only control but not post-activation NK cells contained populations with high levels of granzyme B and perforin. C. NK cells that had been activated in vivo in B16-bearing mice (left) or in vitro (right) and control NK cells were sorted and expanded in IL-2. Lysis assays revealed reduced cytotoxicity of post-activation NK cells both towards B16 (upper) and towards MC38 cells (lower) when compared to control NK cells. Data are shown +/− SD. Analyses were done in at least three independent experiments giving similar results.