Altered Toll-Like Receptor Signalling in Children with Down Syndrome

Abstract

Toll-like receptors (TLRs) are the key in initiating innate immune responses. TLR2 is crucial in recognising lipopeptides from gram-positive bacteria and is implicated in chronic inflammation. Children with Down syndrome (DS) are prone to infections from these pathogens and have an increased risk of autoimmunity. Sparstolonin B (SsnB) is a TLR antagonist which attenuates cytokine production and improves outcomes in sepsis. We hypothesised that TLR signalling may be abnormal in children with DS and contribute to their clinical phenotype. We evaluated TLR pathways in 3 ways: determining the expression of TLR2 on the surface of neutrophils and monocytes by flow cytometry, examining the gene expression of key regulatory proteins involved in TLR signal propagation, MyD88, IRAK4, and TRIF, by quantitative PCR, and lastly determining the cytokine production by ELISA following immunomodulation with proinflammatory stimuli (lipopolysaccharide (LPS), Pam3Csk4) and the anti-inflammatory agent SsnB. We report TLR2 expression being significantly increased on neutrophils, total monocytes, and intermediate and nonclassical monocytes in children with DS (n=20, mean age 8.8±SD 5.3 years, female n=11) compared to controls (n=15, mean age 6.2±4.2 years, female n=5). At baseline, the expression of MyD88 was significantly lower, and TRIF significantly raised in children with DS. The TLR antagonist SsnB was effective in reducing TLR2 and CD11b expression and abrogating cytokine production in both cohorts. We conclude that TLR signalling and the TLR2 pathway are dysregulated in DS, and this disparate innate immunity may contribute to chronic inflammation in DS. SsnB attenuates proinflammatory mediators and may be of therapeutic benefit.

Immune Dysregulation in Children With Down Syndrome

“…Non-classical monocyte have been implicated in various disease states such as cancer, sepsis and chronic inflammation (51). We reported significantly elevated TLR-4 on non-classical monocytes in children with DS vs. controls (43), and greater TLR-2 expression on intermediate and non-classical sub-types (52). This portrays a pro-inflammatory phenotype of monocyte subpopulations in DS.…”

“…It is possible that dysregulation of this receptor and its pathways may be abnormal in DS, and our research on these immune signals supports this theory. Indeed, anomalous TLR2 signaling has been associated with unregulated proinflammatory cytokine production and autoimmunity (52,82).…”

Perinatal Opioid Exposure Primes the Peripheral Immune System Toward Hyperreactivity

“…Specifically, biomarkers in neonates could provide estimation of extent of immune system abnormalities and CNS injury and provide pharmacodynamic support to guide duration or degree of treatment for neonatal opioid withdrawal syndrome or supportive care in neonatal intensive care units. In this context, durable changes in PBMC reactivity may be an effective biomarker, and clinical utility may prove high given the ease of access to these cells and well-defined clinical stimulation protocols ( 37 , 43 ). However, while these in vitro PBMC assays are clinically relevant, they are distinctly different than studying the complex, multidimensional in vivo response to inflammation, sepsis, and systemic sensitization catalyzed by an LPS challenge.…”

“…Here, we extend our investigation of opioid-induced inflammation by thoroughly defining the peripheral immune signaling and reactivity of opioid-exposed PBMCs using an established in vitro assay and biomarker platform ( 35 , 37 , 43 – 50 ). These data enhance the understanding of important inflammatory mechanisms, an essential step to inform future development of appropriate therapeutic interventions for infants who are exposed to opioids during gestation.…”

Autoimmunity and Genetic Syndromes: A Focus on Down Syndrome

“…TLRs are integral plasma membrane proteins that initiate a signaling cascade following a broad range of endogenous and exogenous stimuli, robustly activating the innate immune system. Accurate regulation of TLR pathways is crucial not only for protection against infections but also for prevention of damages deriving from an excess of cytokine production and the consequent autoimmunity that characterizes individuals with DS [ 23 ].…”