Modulatory Effects of Pb²⁺ on Virally Challenged Chicken Macrophage (HD‐11) and B‐Lymphocyte (DT40) Cell Lines In Vitro

Abstract

Elevated levels of lead have been found in waterfowl, due to human activities. Lead may cause immunomodulatory effects, but the mechanisms are largely unknown, especially after viral challenges. To characterize avian immunomodulatory hazards of lead (Pb)2+, we used chicken macrophage (HD‐11) and B‐lymphocyte (DT40) cell lines, as in vitro models for the innate and adaptive immune systems, respectively. The cells were activated via toll‐like receptor‐3 by polyinosinic–polycytidylic acid sodium salt (poly I:C), mimicking viral infections. Our results indicate that Pb2+ is cytotoxic to both cell lines, macrophages being more sensitive. De novo synthesis of glutathione plays an important role in protecting macrophages from Pb2+ intoxication, which might also be closely involved in the induction of nitric oxide after Pb2+ exposure. Stimulatory effects on cell proliferation were noticed at noncytotoxic Pb2+ concentrations as well. Exposure to Pb2+ could also affect the inflammatory status by inhibiting the pro‐inflammatory interferon (IFN)‐γ while promoting the production of anti‐inflammatory type I IFNs in both macrophages and B‐cells, and increasing intracellular IgM levels in B‐cells. These results suggest that the immunomodulatory effects of Pb2+ in birds are probably closely associated with disruption of immune cell proliferation and cytokine production, potentially causing disorders of the avian immune system. Environ Toxicol Chem 2020;39:1060–1070. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC

Modulatory Effects of Mercury (II) Chloride (HgCl2) on Chicken Macrophage and B‐Lymphocyte Cell Lines with Viral‐Like Challenges In Vitro

“…The poly I:C was reported to be recognized by TLR3, triggering several pathways such as nuclear factor κB (NF‐κB) and interferon receptor factors (IRFs) pathways, resulting in generation of a spectrum of cytokines including proinflammatory cytokines (e.g., IL‐8 and IL‐18) via the NF‐κB pathway and antiviral type I IFNs (IFN‐α and ‐β) via IRFs pathways (Alexopoulou et al, 2001; Moynagh, 2005; Sen & Sarkar, 2005; Kawasaki & Kawai, 2014). Our results demonstrated a significant increase in IFN‐α levels due to Hg 2+ exposure in both cell lines, especially DT40 cells (Figure 6C and D), similar to what was observed in Pb 2+ ‐exposed HD‐11 and DT40 cells (Han et al, 2020). Although the expression of type I IFNs was documented to be lifted in HD‐11 cells after 2 h of incubation with poly I:C (Peroval et al, 2013), different IFN‐α levels after poly I:C activation were not found in the qPCR or the ELISA assays after 24 h of exposure in the present study.…”

“…Compared with other trace metal ions, Hg 2+ has a relatively high toxicity. For example, the toxicity of lead (Pb) 2+ was evaluated in the same cell types with much higher EC50 values, namely, 480 μM for HD‐11 macrophages and 1700 μM for DT40 lymphocytes (Han et al, 2020 ). Therefore, although inorganic Hg 2+ is generally regarded to be less toxic than MeHg, it could still be a trace metal ion of concern.…”

“…Downregulation of inducible nitric oxide synthase in cells of the J774A.1 murine macrophage cell line by Hg 2+ was demonstrated in both gene expression profiles as well as protein levels (Kim et al, 2002 ). However, increased nitric oxide levels were found in activated macrophage cell lines after noncytotoxic levels of cadmium (Cd) 2+ and Pb 2+ exposure (García‐Mendoza et al, 2019 ; Han et al, 2020 ), suggesting possible deviating mechanisms among divalent trace metal irons. Once the GSH synthesis was blocked by BSO, less nitric oxide was produced by activated HD‐11 cells exposed to Hg 2+ between 0.5 and 5 µM (Figure 4 ).…”

Toxic metal exposure as a possible risk factor for COVID-19 and other respiratory infectious diseases

“…Lead inhalation in sensitized guinea pigs was shown to alter IFN-γ/IL-4 ratio, being indicative of reduction in Th1/Th2 balance ( Boskabady et al, 2012 ). Pb 2+ was also shown to be toxic to both B-lymphocytes and especially macrophages, also resulting in reduced IFN-γ production and causing aberrant immune response to viral and bacterial pathogens ( Han et al, 2020 ). These findings corroborate the observed inverse correlation between blood lead levels and T cell count in Pb-exposed subjects ( Mishra et al, 2010 ).…”

Increased cytotoxicity of Pb2+ with co-exposures to a mitochondrial uncoupler and mitochondrial calcium uniporter inhibitor

“…While the added concentrations of Pb 2+ selected for this study do not cause overt cell death on their own, they are associated with alterations in other markers of cellular health at these low levels. 14,[32][33][34] It is crucial that we understand how co-exposures may exacerbate specic cellular mechanisms that may lead to the observed additive toxicity. An in-depth knowledge of the pathways that become disrupted in the context of specic chemical mixtures is essential to the eld of predictive toxicology in mixture work.…”