Wang Qi, Westra Johanna, van der Geest Kornelis S M, Moser Jill, Bijzet Johan, Kuiper Timara, Lorencetti Pedro G, Joosten Leo A B, Netea Mihai G, Heeringa Peter, Brouwer Elisabeth, Boots Annemieke M H
Department of Rheumatology and Clinical Immunology, University of Groningen, University Medical Center Groningen, Hanzeplein 1, P.O. Box 30001, 9700 RB Groningen, The Netherlands.
Department of Critical Care, University of Groningen, University Medical Center Groningen, Hanzeplein 1, P.O. Box 30001, 9700 RB Groningen, The Netherlands; Department of Pathology and Medical Biology, University of Groningen, University Medical Center Groningen, Hanzeplein 1, P.O. Box 30001, 9700 RB Groningen, The Netherlands.
Exp Gerontol. 2016 Jun;78:39-46. doi: 10.1016/j.exger.2016.02.016. Epub 2016 Mar 2.
Human aging is associated with remodeling of the immune system. While most studies on immunosenescence have focused on adaptive immunity, the effects of aging on innate immunity are not well understood. Here, we investigated whether aging affects cytokine responses to a wide range of well-defined pattern recognition receptor (PRR) ligands, such as ligands for Toll-like receptors (TLRs), C-type lectin receptors (CLRs), NOD-like receptors (NLRs), retinoic-acid-inducible gene-I like receptors (RLRs) and the cytosolic DNA sensor absent in melanoma 2 (AIM2).
Blood was collected from 16 young (20-39 years) and 18 elderly (60-84 years) healthy participants. Pro-inflammatory cytokine (TNF-α, IL-1β, IL-6, and IL-8) production in a whole blood assay (WBA) after stimulation with TLR ligands (Pam3csk4, poly(I:C), LPS, CpG), CLR ligand (β-glucan), NLR ligand (MDP), RLR ligands (5'ppp-dsDNA and poly(I:C)/lyovec) and the AIM2 ligand (poly(dA:dT) was assessed by ELISA. TLR2 and TLR4 expression by leukocytes and monocytes was determined by flow-cytometry. Expression of AIM2 by peripheral blood mononuclear cells (PBMC) was assessed by qRT-PCR and Western blot.
Cytokine responses to Pam3csk4, poly(I:C) and CpG, β-glucan, MDP, 5'ppp-dsDNA and poly(I:C)/lyovec were comparable between young and old participants. We observed a higher IL-8 response following stimulation of elderly blood samples with the TLR4 ligand LPS, which was associated with higher proportions of TLR4 expressing monocytes. Interestingly, stimulation of whole blood cells with the AIM2 ligand poly(dA:dT) resulted in significantly lower cytokine responses in old participants. Moreover, these lower cytokine responses were associated with lower AIM2 protein expression and activation in PBMC of old participants.
Our findings reveal an age-dependent reduction of AIM2 expression and activation which may explain reduced cytokine responses to the cytosolic DNA mimic poly(dA:dT) in healthy elderly individuals. Reduced AIM2-mediated sensing with age may contribute to increased vulnerability to bacterial or viral infections in the elderly.
人类衰老与免疫系统重塑相关。虽然大多数关于免疫衰老的研究都集中在适应性免疫上，但衰老对固有免疫的影响尚未得到充分了解。在此，我们研究了衰老是否会影响细胞因子对多种明确的模式识别受体（PRR）配体的反应，例如Toll样受体（TLR）、C型凝集素受体（CLR）、NOD样受体（NLR）、维甲酸诱导基因I样受体（RLR）以及黑色素瘤2中缺失的胞质DNA传感器（AIM2）的配体。
采集16名年轻（20 - 39岁）和18名老年（60 - 84岁）健康参与者的血液。在用TLR配体（Pam3csk4、聚肌胞苷酸、脂多糖、CpG）、CLR配体（β-葡聚糖）、NLR配体（MDP）、RLR配体（5'三磷酸双链DNA和聚肌胞苷酸/脂质体）以及AIM2配体（聚（dA:dT））刺激后，通过酶联免疫吸附测定（ELISA）评估全血检测（WBA）中促炎细胞因子（肿瘤坏死因子-α、白细胞介素-1β、白细胞介素-6和白细胞介素-8）的产生。通过流式细胞术测定白细胞和单核细胞中TLR2和TLR4的表达。通过定量逆转录聚合酶链反应（qRT-PCR）和蛋白质免疫印迹法评估外周血单个核细胞（PBMC）中AIM2的表达。
年轻和老年参与者对Pam3csk4、聚肌胞苷酸、CpG、β-葡聚糖、MDP、5'三磷酸双链DNA和聚肌胞苷酸/脂质体的细胞因子反应相当。我们观察到，在用TLR4配体脂多糖刺激老年血液样本后，白细胞介素-8反应更高，这与表达TLR4的单核细胞比例更高有关。有趣的是，用AIM2配体聚（dA:dT）刺激全血细胞后，老年参与者的细胞因子反应明显较低。此外，这些较低的细胞因子反应与老年参与者PBMC中AIM2蛋白表达和激活较低有关。
我们的研究结果揭示了AIM2表达和激活的年龄依赖性降低，这可能解释了健康老年人对胞质DNA模拟物聚（dA:dT）的细胞因子反应降低的原因。随着年龄增长，AIM2介导的传感减少可能导致老年人对细菌或病毒感染的易感性增加。
