Differentiation of IL-22 levels in inflammatory diseases using a high sensitivity ELISA

Introduction

Interleukin-22 (IL-22), an IL-10 cytokine family member⁽¹⁾, is produced by a variety of immune cells including Th1, TH17, and Th22 T helper cells, CD8+ T-cells, NK cells, ILC3, neutropils, and macrophages⁽²⁾. IL-22 cruically participates in regulating the integrity of epithelisal barriers by modulating inflammation mucus production, additional aspects of wound healing⁽³⁾, and has been noted to be substantially induced in patients with various chronic inflammatory conditions. IL-22's upregulation in psoriasis (PS), rheumatoid arthritis (RA), systemic lupus erythematosus⁽⁴⁾ (SLE), inflammatory bowel disease⁽⁵⁾, Crohn's disease⁽⁶⁾, cystic fibrosis⁽⁷⁾, and atopic dermatisit⁽⁸⁾ (AD) has been well documented, with IL-22 often considered a hallmark of IL-17 driven immune responses⁽⁹⁾. Furthermore, IL-22 protein has been proposed as a stratification biomarker for psoriatic arthritis therapeutic choice between IL-17 and TNF inhibitions⁽¹⁰⁾, to correlate with the severity of clinical sequelae of Sjogren's Syndrome⁽¹¹⁾, and IL-22 mRNA expression stratifies AD responses to fezakinumab⁽⁹⁾. In healthy individuals, IL-22 activity resulting from low level expression may be functionally neutralized, at least in selected tissues such as the intestinal tract, by the binding to soluble IL-22 binding protein (IL-22BP) expressed locally by dendritic cells⁽¹²⁾. However, in these pathologies, inhibition of IL-22 by IL-22BP is presumably overcome by elevated expression of IL-22 protein.

First published in British Journal of Dermatology, Volume 188, Issue Supplement_3, June 2023, ljad162.049, https://doi.org/10.1093/bjd/ljad162.049

Objective

Explore ranges of IL-22 serum concentrations to differentiate between healthy donors (HD) and select autoimmune disease patients with a simple-to-use, high sensitivity ELISA.

Methods

A commercial sandwich ELISA (PBL Assay Science, 41701-1) quantifying human IL-22 was characterized and used to assess IL-22 concentration in sera from HD and patients exhibiting one of several autoimmune patients.

Results

This high sensitivity ELISA,m having a manufacturer-stated LLOQ of 0.78 pg/ml, exhibit good assay precision, dilutional linearity, and spike recovery using HD serum. Parallelism was demonstrated using serum samples from four AD patients and three HD. Addition of a 10-to-100-fold mass excess of exgenous recombinant IL-22BP reduced the ability of the assay to quantify IL-22 suggesting that at least one antigenic region recognized by ELISA antibodies may be sterically hindered by IL-22BP binding to IL-22. However, such high levels of 10 and 100 ng/ml of IL-22BP are unlikely to be achieved in vivo, and therefore may not adversely affect quantitation of physiological levels of IL-22 protein by this assay.

Commercially sourced HD sera (NHS) concentrations of IL-22 exceeded the assay LLOQ in 23 of 24 samples (96%) with a mean IL-22 concentration of 1.84 +/- 1.33 pg/ml. Commercial sera from AD (n=10, 100%). PS (n=10, 100%), RA (n=10, 100%), SLE (n=10, 100%) patients were similarly analyzed and yielded mean levels of 14.8 +/- 11.2, 5.1 +/- 0.91, and 3.1 +/- 0.74 pg/ml, respectively.

Conclusions

IL-22 measured in AD (and PS) sera exhibit sufficiently broad ranges of concentrations such that statistical differences between AD and all other groups were not readily achievable with this number of samples. Notably, these commercially obtained serum samples were not controlled for overall severity of any disease at the time of sample collection, Sample sets were randomly obtained from a population of individuals self-identifying as AD sufferers, as were the other patient samples. With mean serum IL-22 in AD appearing to trend as substantially elevated, an opportunity exists to explore IL-22 trends along with other biomarkers in clinically identified and possibly symptom-stratified populations of AD patients. Should this trend toward IL-22 elevation be fully substantiated in AD, therapeutic stratification and precision medicine approaches may be conceivable based on serum IL-22 protein concentrations, supporting other investigators' earlier work examining IL-22 mRNA⁽⁹⁾. The baseline readability of endogenous IL-22 in HD sera using this ELISA is also highly advantageous.

Ketwords

Atopic dermatitis, IL-22, ELISA, autoimmune, basal level

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