Abstract

Peripheral blood mononuclear cell (PBMC) cytotoxicity against S. typhi (wild type or mutant strain TYT1231)-infected U937 cells was significantly higher than its lytic effect against noninfected cells (control) at the various effector-to-target cell ratio used (30:1, 50:1 and 70:1). Natural killer cell activity [expressed as % specific lysis (mean ± SEM); 30:1 (25.4 ± 3.6, 25.1 and 16.3 = 3.3); 50:1 (27.8 ± 3.7, 26.7 ± 4.5 and 20.9 ± 2.9) and 70:1 ratio (33.2 ± 5.9, 29.4 ± 4.2 and 22.8 ± 2.8), respectively] appeared to be dependent on such ratios and independent of the S strain studied. Most (80%) of individual samples tested showed at least a 20% specific lysis increase over their own control; essentially no changes or smaller increases in NKC activity were observed in all other samples. Similar results were obtained when using highly purified NKC (HPNKC) preparations as effector cells [NKC activity (mean ± SEM); 5:1 (46.2 ± 4.7, 43.2 ± 5.0 and 25.2 ± 2,3) and 10:1 effector-to-target cell ratio (49.3 ± 4.9, 44.7 ± 5.2 and 27.2 ± 2.6, respectively)]. All individual samples tested showed at least a 20% specific lysis increase over their own control. These results show that S. typhi-infected U937 cells are a significantly better target for NKCs than control cells and indicate that intracellular bacteria survival capacity is not a critical factor for infected cells becoming a NKC target.