FIG. 1.

Correlations of serum IL-18 levels with NK cell numbers and cytotoxicity. IL-18 concentrations in the sera of 26 HIV-infected persons were measured by a commercial ELISA kit, and the absolute numbers of different NK cells subsets present in their peripheral blood after gating on the viable lymphocyte population were determined by flow cytometry. (A) Representative flow cytometry data showing the gates used to identify the three different subsets of NK cells. The panel on the right shows results for CD3⁻ CD16⁺ CD56⁺ NK cells. (B to D) Pearson correlations between serum concentrations of IL-18 and their absolute numbers of CD3⁻ CD56⁺ (B), CD56⁺ CD16⁺ (C), and CD3⁻ CD16⁺ (D) NK cells. The two parameters showed a statistically significant negative correlations (P = 0.04; r = −0.40 for panel B), (P = 0.006; r = −0.52 for panel C) and (P = 0.008; r = −0.52 for panel D). (E) Spontaneous NK cell activities of freshly isolated PBMC from these patients against K562 cells in a standard ⁵¹Cr-release assay. The serum IL-18 concentrations were plotted against NK cell-mediated cytotoxicities of the PBMC from HIV/AIDS patients. A bimodal effect of the serum IL-18 concentrations on NK cell-mediated cytotoxicities is evident.