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Human NK Cells Differ More in Their KIR2DL1-Dependent Thresholds for HLA-Cw6-Mediated Inhibition than in Their Maximal Killing Capacity

Figure 3

The threshold in MHC-I mediated NK cell inhibition depends on the expression level of KIR2DL1.

A) Lysis of different target cells by three NK cell clones, as determined by radioactive release assays, plotted against target MHC-I cell surface expression. Open symbols represent lysis of untransfected 221 cells. Circles show a clone inhibited by MHC; triangles show a clone not inhibited by MHC; and squares show a clone whose activity increased as function of target MHC level. B) Lysis of target cells by one NK cell clone as a function of target MHC-I cell surface expression. A sigmoid curve was fitted to the data (using the Origin software) and the amount of MHC-I required to inhibit lysis to half its maximum, the EC50, was determined. C) Where inhibition of lysis was observed, EC50 was determined for different clones phenotyped for KIR2DL1, NKG2A, LIR1 and CD94 expression. Each clone may express one or more receptors. Medians are indicated and statistical significance of differences was determined with the non-parametric Mann-Whitney test. **P<0.005; ns, not significant. D) Correlation between EC50 and receptor expression level, obtained by performing a regression analysis to evaluate the contribution of each receptor – or combination of receptors – to the EC50 data. R2 is the correlation measure, and the higher it is, the higher the correlation. More details are given in Table S1.

Figure 3

doi: https://doi.org/10.1371/journal.pone.0024927.g003