Interleukin-7 receptor α-chain haplotypes differentially affect soluble IL-7 receptor and IL-7 serum concentrations in children with type 1 diabetes

Exploring Interleukin Levels in Type 1 Diabetes and Periodontitis: A Review with a Focus on Childhood

Diabetes can trigger an increase in cytokine levels leading to the production of C-reactive protein and fibrinogen. These molecules promote subclinical inflammation, causing the expression of adhesive molecules and endothelial dysfunction. Despite the lack of a comprehensive panel for single-nucleotide polymorphisms (SNPs) for interleukins associated with type 1 diabetes mellitus (T1DM), understanding the inflammatory role of SNPs is crucial because periodontitis, the sixth complication of diabetes, is influenced via these genetic variations. This review focuses on the interleukin levels in T1DM patients with and without periodontitis, with a particular focus on childhood and on SNPs when reported. A search of PubMed and Scopus identified 21 relevant studies from the past five years. Several ILs were analyzed, emphasizing that T1DM still needs to be thoroughly explored regarding an IL polymorphisms panel; however, the last five years have led to the increased independence of this condition, causing autonomous inflammatory effects, which require further investigation. The periodontitis and T1DM association in children and adolescents represents a severe gap in the literature that should be filled; this scarce presence of studies serves as motivation for further clinical research.

Interleukin-7-dependent nonclassical monocytes and CD40 expression are affected in children with type 1 diabetes

The important role of IL-7 in the generation of self-reactive T-cells in autoimmune diseases is well established. Recent studies on autoimmunity-associated genetic polymorphisms indicated that differential IL-7 receptor (IL-7R) expression of monocytes may play a role in the underlying pathogenesis. The relevance of IL-7-mediated monocyte functions in type 1 diabetes remains elusive. In the present study, we characterized monocyte phenotype and IL-7-mediated effects in children with type 1 diabetes and healthy controls with multicolor flow cytometry and t-distributed Stochastic Neighbor-Embedded (t-SNE)-analyses. IL-7R expression of monocytes rapidly increased in vitro and was boosted through LPS. In the presence of IL-7, we detected lower monocyte IL-7R expression in type 1 diabetes patients as compared to healthy controls. This difference was most evident for the subset of nonclassical monocytes, which increased after IL-7 stimulation. t-SNE analyses revealed IL-7-dependent differences in monocyte subset distribution and expression of activation and maturation markers (i.e., HLA-DR, CD80, CD86, CD40). Notably, monocyte CD40 expression increased considerably by IL-7 and CD40/IL-7R co-expression differed between patients and controls. This study shows the unique effects of IL-7 on monocyte phenotype and functions. Lower IL-7R expression on IL-7-induced CD40_high monocytes and impaired IL-7 response characterize monocytes from patients with type 1 diabetes.

Biological functions and therapeutic opportunities of soluble cytokine receptors

Cytokines control the immune system by regulating the proliferation, differentiation and function of immune cells. They activate their target cells through binding to specific receptors, which either are transmembrane proteins or attached to the cell-surface via a GPI-anchor. Different tissues and individual cell types have unique expression profiles of cytokine receptors, and consequently this expression pattern dictates to which cytokines a given cell can respond. Furthermore, soluble variants of several cytokine receptors exist, which are generated by different molecular mechanisms, namely differential mRNA splicing, proteolytic cleavage of the membrane-tethered precursors, and release on extracellular vesicles. These soluble receptors shape the function of cytokines in different ways: they can serve as antagonistic decoy receptors which compete with their membrane-bound counterparts for the ligand, or they can form functional receptor/cytokine complexes which act as agonists and can even activate cells that would usually not respond to the ligand alone. In this review, we focus on the IL-2 and IL-6 families of cytokines and the so-called Th2 cytokines. We summarize for each cytokine which soluble receptors exist, were they originate from, how they are generated, and what their biological functions are. Furthermore, we give an outlook on how these soluble receptors can be exploited for therapeutic purposes.

IL7RA genetic variants differentially affect IL-7Rα expression and alternative splicing: a role in autoimmune and infectious diseases?

Interleukin-7 receptor α chain (IL-7Rα) single nucleotide polymorphisms (SNPs) are associated with susceptibility to immunopathologies like autoimmune and inflammatory diseases. The current hypothesis about underlying mechanisms is based on the regulation of IL-7 availability for self-reactive T cells by influencing the generation of a soluble (s)IL-7Rα variant. This assumption was mainly predicated on the well-defined IL7RA SNP rs6897932, which affects alternative splicing and causes aberrant generation of the sIL-7Rα variant with potential effects on the IL-7 serum reservoir. However, more recent studies shed light on novel functions of autoimmunity risk-associated IL7RA SNPs and characterized the largely neglected effect of rs6897932 on membrane (m)IL-7Rα expression. These findings as well as a described role of impaired mIL-7Rα expression and IL7RA SNP influence on chronic infectious diseases necessitates the reevaluation of previous findings on the role of IL7RA SNPs in immunopathology.

Higher Interleukin-7 serum concentrations in patients with cystic fibrosis correlate with impaired lung function

BACKGROUND

Patients with cystic fibrosis (CF) are highly susceptible to infection and colonization of pulmonary epithelia. Repeated and chronic infections may affect disease course and efficacy of host immune protection. Higher Interleukin (IL)-7 serum levels, indicating impaired T-cell response to IL-7, have been described for chronic viral and mycobacterial infections.

METHODS

Time course measures of IL-7 serum concentrations in patients with CF (n = 164; n = 78 for the second time point) and healthy controls (n = 60) were done. CF patients were characterized for disease severity parameters as well as infection status and association with IL-7 serum levels was determined.

RESULTS

CF patients had significantly higher IL-7 serum concentrations as compared to healthy controls (9.79 pg/ml, IQR 6.76-13.6 versus 4.55 pg/ml, IQR 2.76-9.51, p < .001). IL-7 serum levels were negatively correlated with individual CF patient's BMI (r = -0.19, p = .021) and a tendency of increased IL-7 levels in Staphylococcus aureus infected CF patients was found. Linear regression of multiple parameters revealed significant negative correlation of FEV1_%pred with IL-7 serum concentrations in patients with CF (ß-coefficient: -0.04, 95% confidence interval [-0.08; -0.003], p = .034). Time course analyses after 1 year +/- 6 months showed increased IL-7 serum levels (time point 1:9.26 pg/ml, IQR 6.94-13.12 time point 2:10.86 pg/ml, IQR 9.14-14.76, p = .016) that correlated negatively with decreased FEV1_%pred during CF disease course.

CONCLUSIONS

High IL-7 serum levels were found in CF patients and correlated with impaired lung function during CF disease course. As a candidate biomarker of T-cell dysfunction, higher IL-7 serum level may also indicate worsened immune competence of patients with CF.