Figure 8. NK cells mediate specific lysis of activated CD8⁺ T cells in the absence of 2B4 in vitro and in vivo.

(A) WT (black bars) or 2B4-KO (white bars) LAK cell killing (mean ± SD) of WT CD8⁺ T cell targets, activated in vitro with various doses of ConA. (B) Specific lysis (mean ± SD) of WT or CD48-KO ConA-activated CD8⁺ T cells by WT (left) or by Prf1-KO (right) LAK cells is shown at various effector to target (E/T) ratios. (C and D) A modified in vivo cytotoxicity assay was done by injecting CFSE-labeled splenocytes (3 × 10⁷) from LCMV-infected (day 4 p.i.) congenic (Ly5.1⁺) WT mice into uninfected or LCMV-infected (day 4 p.i.) WT and 2B4-KO mice (Ly5.2⁺, n = 5–6/group), some of which were depleted of NK cells 1 day prior to infection. Five hours after transfer, the proportion of activated (CD44^hiCD43[1B11]⁺) donor (Ly5.1⁺CFSE⁺) cells was determined in each mouse. (C) Representative CD44 and CD43(1B11) expression by donor Ly5.1⁺CFSE⁺ CD8⁺ T cells. Numbers are the percentage of donor (Ly5.1⁺CFSE⁺) CD8⁺ T cells that are CD44^hiCD43(1B11)⁺ for the representative sample shown. (D) Top graphs depict the percentage of activated CD44^hiCD43(1B11)⁺ donor (Ly5.1⁺CFSE⁺) CD8⁺ T cells in isotype- (left) or anti-NK1.1–treated (right) WT and 2B4-KO mice. Lower left plot demonstrates the proportion of naive phenotype (CD44^loCD43[1B11]^–) donor (Ly5.1⁺CFSE⁺) CD8⁺ T cells in isotype-treated WT and 2B4-KO mice. Lower right plot depicts the percentage of activated CD44^hiCD43(1B11)⁺ donor (Ly5.1⁺CFSE⁺) CD8⁺ T cells in Prf1-KO and 2B4/Prf1-KO mice. Results are presented as mean ± SD. **P < 0.01 (2-tailed unpaired Student’s t test). Data are from 1 of 3 similar experiments.