Data from: Reduced internalization of TNF-ɑ/TNFR1 down-regulates caspase dependent phagocytosis induced cell death (PICD) in neonatal monocytes

Phagocytosis-induced cell death (PICD) is diminished in cord blood monocytes (CBMO) as compared to cells from adults (PBMO) due to differences in the CD95-pathway. This may support a prolonged pro-inflammatory response with sequels of sustained inflammation as seen in neonatal sepsis. Here we hypothesized that TNF-α mediated induction of apoptosis is impaired in CBMO due to differences in the TNFR1-dependent internalization. Monocytes were infected with Escherichia coli-GFP (E. coli-GFP). Monocyte phenotype, phagocytic activity, induction of apoptosis, and TNF-α/TNF-receptor (TNFR) -expression were analysed. In the course of infection TNF-α-secretion of CBMO was reduced to 40% as compared to PBMO (p<0.05). Neutralization of TNF-α by an αTNF-α antibody reduced apoptotic PICD in PBMO four-fold (p < 0.05 vs. infection with E. coli). PICD in CBMO was reduced 5-fold compared to PBMO and showed less responsiveness to αTNF-α antibody. CBMO expressed less pro-apoptotic TNFR1, which, after administration of TNF-α or infection with E. coli was internalized to a lesser extent. With similar phagocytic capacity, reduced TNFR1 internalization in CBMO was accompanied by lower activation of caspase-8 (p < 0.05 vs. PBMO). Stronger caspase-8 activation in PBMO caused more activation of effector caspase-3 and apoptosis (all p < 0.05 vs. PBMO). Our results demonstrate that TNFR1 internalization is critical in mediating PICD in monocytes after infection with E.coli and is reduced in CBMO.与成人外周血单核细胞（peripheral blood monocytes, PBMO）相比，脐血单核细胞（cord blood monocytes, CBMO）中的吞噬诱导的细胞死亡（Phagocytosis-induced cell death, PICD）因CD95通路的差异而减弱，这可能会导致促炎反应持续延长，进而出现新生儿败血症中所见的持续性炎症后遗症。本研究假设，由于依赖肿瘤坏死因子受体1（Tumor necrosis factor receptor 1, TNFR1）的内化过程存在差异，CBMO中肿瘤坏死因子-α（Tumor necrosis factor-α, TNF-α）介导的细胞凋亡诱导作用受损。研究人员将单核细胞经绿色荧光蛋白标记的大肠杆菌（Escherichia coli-GFP, E. coli-GFP）感染，随后对单核细胞表型、吞噬活性、细胞凋亡诱导情况以及TNF-α/肿瘤坏死因子受体（TNFR）的表达水平进行了分析。感染过程中，CBMO的TNF-α分泌量仅为PBMO的40%（p<0.05）。通过抗TNF-α抗体中和TNF-α，可使PBMO的凋亡性PICD降低四倍（与大肠杆菌感染组相比，p < 0.05）。CBMO中的PICD较PBMO降低了五倍，且对抗TNF-α抗体的响应性更弱。CBMO表达的促凋亡型TNFR1水平更低，且在给予TNF-α或感染大肠杆菌后，其TNFR1的内化程度也更低。尽管吞噬能力无显著差异，但CBMO中TNFR1内化的减少伴随半胱天冬氨酸蛋白酶-8（cysteine aspartate-specific protease 8, caspase-8）的激活水平降低（与PBMO相比，p < 0.05）。PBMO中更强的caspase-8激活可引发更多的效应性半胱天冬氨酸蛋白酶-3（caspase-3）激活及细胞凋亡（所有指标与PBMO相比，p < 0.05）。本研究结果表明，TNFR1内化在大肠杆菌感染后单核细胞的PICD介导过程中发挥关键作用，且该过程在CBMO中受到削弱。