Comparison of europium and chromium release assays: Cytotoxicity in healthy individuals and patients with cervical carcinoma

Natural killer !NK) and lymphokine-activated killer (LAI) cell activities were measured in peripheral blood obtained from healthy women to compare a standard Cr-51 release assay with a nonradioactive europium (EU(3+)) release assay based on time-resolved fluorescence. The two types of cytotoxicity assays were first compared in paired determinations performed on 28 samples of peripheral blood mononuclear cells obtained from healthy women who had normal pap smears or no biopsy evidence of cervical squamous intraepithelial lesions (SIL). Target cells (NK-sensitive K562 and NK-resistant Raji cell lines) were labeled with Eu3+ only, Cr-51 only, or both labels and compared in cytotoxicity assays using fresh or interleukin 2 (IL-2)-activated effector cells. Spontaneous release in the Eu3+ release assay was comparable to that observed in the Cr-51 release assay, but maximum Eu3+ release always exceeded that of Cr-51. In 4-h assays, specific release of Eu3+ from target cells was more rapid than that of Cr-51, consistently resulting in 30 to 40% higher levels of activity. However, a significant linear correlation (P < 0.001) was observed between cytotoxicity levels based on measurements of Eu3+ and Cr-51 release in 4-h assays. The Eu3+ release assay was then used to measure NR and LAK activities in the peripheral blood of women with cervical SIL or cervical squamous cell carcinoma (SCC). Mean Nh activity of women with advanced SIL (121 lytic units [LU]) or SCC (93 LU) was found to be similar to that of controls (101 LU) or patients with normal cervical biopsies (30 LU), as was the ability to generate IL-2-stimulated Nh:activity. However, LAK activity during 18 h of incubation in the presence of IL-2 was reduced in patients with cervical SCC (P < 0.05) compared with that in normal controls. Results of Cr-51 assays performed in parallel with patient samples gave comparable results. Advantages of Eu3+ release assays for routine evaluation of cytotoxicity are discussed.