Mercury (Hg), a chemical pollutant, poses a significant risk to human health globally. It is considered a hazardous substance present on the Earth's surface. The World Health Organization (WHO) has included Hg among the top 10 chemicals that greatly endanger public health (World Health Organization, 2020). In its inorganic forms, such as mercuric chloride (HgCl₂), where mercury is present as the Hg2+ ion (+2 oxidation state), it is commonly emitted through industrial processes and can cause significant harm to human biological systems, including the immune system (Mehmood et al., 2024).

The toxicity of HgCl2 is closely associated with its ability to generate reactive oxygen species (ROS), leading to oxidative stress, cell damage, chronic inflammation, and derangement of essential biochemical functions (Ajsuvakova et al., 2020; Liu et al., 2021). Recent studies have shown that inorganic Hg compounds can induce lipid peroxidation, and cause deoxyribonucleic acid (DNA) mutations, leading to cell apoptosis or necrosis (Pollard et al., 2019; Waheed et al., 2020; Wu et al., 2024). In addition, exposure to HgCl2 has been associated with changes in the immune system, such as microglial activation in the central nervous system (CNS), and the release of pro-inflammatory cytokines that exacerbate tissue damage (Liu et al., 2021).

Hg can modulate the activity of various immune cells, including neutrophils, macrophages, natural killer (NK) cells, and B and T lymphocytes, leading to alterations in cytokine production, phagocytic capacity, and lymphocyte proliferation (Anka et al., 2022; Pollard et al., 2019). Additionally, exposure to Hg2+ has been implicated in the induction of autoimmune responses, potentially via molecular mimicry. In this context, Hg2+ forms complexes with host proteins that elicit immune activation, and the resulting autoantibodies may cross-react with unmodified self-antigens due to structural similarities (Wu et al., 2024).

In response to exposure to HgCl2, pro-inflammatory mediators are activated, including NLRP3 (NOD-, LRR- and pyrin domain-containing protein 3) inflammasome, stimulating the secretion of interleukin 1β (IL-1β) and inducing pyroptosis. Furthermore, Hg stimulates the production of interleukin 6 (IL-6) and tumor necrosis factor-α (TNFα), which amplifies the inflammatory response through activation of the nuclear factor-κB (NF-κB) pathway, resulting in cellular damage and immune dysfunctions (Wang et al., 2024).

Exposure to Hg has been associated with significant changes in the purinergic system, contributing to cellular dysfunction and neurological damage. It can also impact the functionality of purinergic receptors and associated enzymes, disrupting purinergic homeostasis and worsening pathological processes (Cruz et al., 2013; Sakamoto et al., 2014; Senger et al., 2006a). Ectonucleotidases are inhibited by Hg, resulting in the accumulation of these nucleotides and the hyperactivation of P2X and P2Y receptors (Senger et al., 2006b). This imbalance in extracellular nucleotide homeostasis promotes exacerbated inflammatory responses and contribute to Hg-associated neurotoxicity (Senger et al., 2006a).

In addition, studies suggest that metals also modulate ionotropic receptors that are part of purinergic signaling, such as the purinergic receptors P2X subtype 7 (P2X7) purinergic receptors (Assmann et al., 2021; Sakamoto et al., 2014). Adenosine A1 and A2A receptors are essential in the regulation of human peripheral blood immune cells. The A1 receptor functions to modulate the immune system, although this is still poorly understood. The A2A receptor has an anti-inflammatory effect, stimulating the production of regulatory T cells. In addition, it inhibits chemokine receptors, reducing inflammation (Zhong et al., 2022).

Human peripheral blood mononuclear cells (PBMCs) are primary cells found in the peripheral blood and they contain a single nucleus (such as lymphocytes, monocytes, NK cells, or dendritic cells) (Kleiveland and Kleiveland, 2015). These cells serve as a line of defense against infection and disease. PBMCs are commonly used to study the behavior of immune cells in response to pathogen exposure, and factors affecting long-term immunity (Derbois et al., 2023; Verhoeckx et al., 2015).

Although Hg2+ can be toxic to various biological systems, little is known about HgCl2‘s effects on peripheral human blood immune cells (Cederbrant and Hultman, 2000; Contrino et al., 1988; dos Santos Chemelo et al., 2021; Roos et al., 2001). Considering the health risks to human health associated with HgCl2 and given that detailed mechanisms of Hg2+ toxicity remain elusive, this study investigated the cytotoxic, pro-oxidative, and inflammatory effects, as well as potential changes in the purinergic system caused by HgCl2 in an in vitro model of PBMCs.