Significant health risk has been brought about by increased level of irradiation from ozone holes, industrial pollutants and nuclear leakages. Although the global ozone holes have been decreased in recent years, the area of ozone holes still increased significantly in some regions, such as Argentina and Antarctica (Ohneiser et al., 2022), which caused increase of ultraviolet (UV) radiation. The smoke dust and waste gas from coal combustion always contain some radioactive metal elements, such as uranium (Yang et al., 2016) and polonium (Ouyang et al., 2018), which may increase the levels of ionizing radiation in atmosphere. Nuclear leakages always lead to significant panic among populations and serious contamination in eco- environment. For instance, Chernobyl accident led to thousands' death and malignant tumors in the surrounding regions, and persistent contamination in local soil and water. In addition, the sewage discharge from Fukushima I Nuclear Power Plant in Japan will lead to massive radioactive elements, such as carbon 14 and iodide 129, enter into global ocean, which may cause death and developmental malformation of aquatic organisms and irradiation-related diseases among coastal residents. Cellular genome instability is the mode of action underlying irradiation-induced impairments, which always causes genetic mutation, developmental malformation and malignant tumors (Richardson and Jasin, 2000). Immune cells are the main targets of irradiation damage, such as lymphocytes (Kanegasaki et al., 2019) and neutrophils (Hu et al., 2023). It has been documented that high dose or long-term irradiation, including UVC and ionizing radiation, can lead to human immune diseases, such as myelodysplastic syndromes (MDS) and leukemia (Griffin et al., 2023; Zharlyganova et al., 2008).

However, the previous mechanistic studies focused on the repair process of DNA damage, which failed to link molecular mechanisms to the disease phenotypes (Mavragani et al., 2017; Zhang et al., 2023). Omics approaches have been used to reveal the molecular events in immune cells exposed to irradiation, such as transcriptomics (Liu et al., 2019) and proteomics (Nishida et al., 2020). Although these omics approaches can provide a global insight of molecular information based on the abundance changes of gene expression, the molecular information is not specific to uncover the causal toxicological mechanism of irradiation-induced immune diseases, because that some gene expression changes may result from the toxicity endpoint (Lujan et al., 2020; Shen et al., 2015). The cascade of molecular events forwards to the toxicity endpoint is critical for illustrating the causal mechanism. In addition, some key gene targets in the cascade could be used as potential biomarkers of disease treatment or diagnosis. For instance, some long non-coding RNAs (lncRNA) have been used as the biomarkers of cancer treatment and diagnosis, e.g. MALAT-1 for lung cancer, because of the stability and specificity of lncRNA in human blood circulation system (Badowski et al., 2022). Therefore, an approved framework which distributes molecular events into the causal links among various biological processes is essential to reveal the toxicological mechanism underlying irradiation-induced immune impairment.

Adverse outcome pathway (AOP) provides an approved framework containing the cascade of molecular events which starts from molecular initiating event (MIE) to adverse outcome (AO). AOP describes a model which contains the development progress of chemical or physical agents-induced toxicity and disease (Song et al., 2020). Assemblages of the AOPs which share one or more biological processes can be interconnected to generate an AOP network. AOP network has been proved to provide the causal mechanism underlying specific phenotypic outcomes (Pogrmic-Majkic et al., 2022; Song et al., 2020; Tian et al., 2022; Xia et al., 2021). Incorporating omics data into the description of key events (KEs) by assignment of pathway annotations (e.g. Gene Ontology) to each KE in the scale of AOP knowledge base (AOP-KB) has been validated in our previous studies (Tian et al., 2022; Tian et al., 2023; Xia et al., 2021).

Here, we revealed toxicological mechanism underlying irradiation-induced immune impairment by integrating transcriptomic dose-response with AOP network analysis. Firstly, we evaluated the dose-response of genome instability in human lymphocytes exposed to two typical irradiations, UVC and Fe ionizing radiation (Fe IR), respectively. Secondly, we used transcriptomic dose-response in human lymphocytes to identify the molecular events, including mRNA and lncRNA, responding to UVC and Fe IR. Moreover, AOP network analyses were performed to map the molecular events to the KE cascade of the AOP which could be caused by the corresponding irradiation. Finally, the molecular mechanisms underlying irradiation-induced immune impairment were linked to the pathway to human leukemia, and a pair of lncRNA-mRNA was identified as potential biomarkers of immune impairment. Our study may provide a novel paradigm for the next-generation risk assessment of the adverse effects of environmental irradiation.