Lptn-mediated apoptosis occurs through Fas/FasL signaling pathway.

(A) Effects of ZB4 and 7C11 anti-Fas mAbs on the Lptn-induced inhibition of proliferation. Proliferation was assessed by [³H]-thymidine incorporation during the last 18 hours of 96-hour culture of CD4⁺ T cells activated via CD3, in the presence or absence of Lptn. Both anti-Fas mAbs (used at 1 μg/mL) were preincubated 1 hour before activation. Results are expressed as the mean count/min values ± SD of 3 separate experiments. (B) Protection by ZB4 mAb against Lptn-induced increase in DNA fragmentation. CD4⁺ T cells were preincubated with 1μg/mL of the antagonist ZB4 anti-Fas mAb prior to CD4⁺ T-cell stimulation for 2 days, as described in “Materials and methods.” Cells were then washed and subjected to the TUNEL assay, according to manufacturer's protocol. For each sample, an aliquot was treated for 10 minutes with DNase I, serving as positive control. After FITC-dUTP and TdT staining, analyses were performed by flow cytometry. Data represent values of mean fluorescence intensity ± SD (error bars) calculated from at least 3 independent experiments. ▪, CD3; ■, CD3 plus ZB4.