Lead at 2.5 and 5.0μM induced aberrant MH-II surface expression through increased MII exocytosis and increased autophagosome formation in Raw 267.4 cells

• Published in: Toxicology in vitro Vol. 27; no. 3; pp. 1018 - 1024
• Main Authors: Kerr, R.P., Krunkosky, T.M., Hurley, D.J., Cummings, B.S., Holladay, S.D., Gogal, R.M.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.04.2013
• Subjects: Animals; Antigen presenting cell; Antigens, CD - metabolism; Autophagy; Autophagy - drug effects; beta-N-Acetylhexosaminidases - metabolism; Cell Line; Cell Proliferation - drug effects; Cell Survival - drug effects; Endosomal trafficking; Environmental Pollutants - toxicity; Exocytosis - drug effects; Histocompatibility Antigens Class II - metabolism; Lead - toxicity; Lysosomal Membrane Proteins - metabolism; Lysosomal-Associated Membrane Protein 2 - metabolism; MHC-II; Mice; MIIC exocytosis; MIIC exocytosis; Antigen presenting cell; Autophagy; Endosomal trafficking; MHC-II
• ISSN: 0887-2333; 1879-3177
• DOI: 10.1016/j.tiv.2013.01.018

► Lead (Pb), at >25μM, increases MHC-II surface expression resulting in immune dysregulation. ► Data on exposure to environmentally relevant Pb levels in macrophages are lacking. ► Environmental Pb exposure inhibited metabolic activity and increased MHC-II surface expression. ► Environmental Pb exposure induced autophagy, and increased MHC-II trafficking, a novel finding. ► Pb exposure is a novel mechanism in which macrophages may enhance self-antigen expression. Aberrant major histocompatibility complex class II (MHC-II) surface expression on antigen presenting cells (APCs) is associated with dysregulated immune homeostasis. Lead (Pb) is known to increase MHC-II surface expression on murine peritoneal macrophages ex vivo at concentrations exceeding 25μM. Little data exist examining this effect at physiologically relevant concentrations. To address this deficit, we examined the effects of Pb on MHC-II surface expression, secondary T-cell activation markers (CD80, CD86, CD40), cell viability, cellular metabolic activity, and β-hexosaminidase activity in RAW 267.4 macrophage cell lines, with changes in cell ultrastructure evaluated by electron and confocal microscopy. Pb induced an increase in MHC-II, CD86, and lysosome-associated LAMP-1 and LAMP-2 surface mean expression during one doubling cycle (17h), which was mirrored by increased β-hexosaminidase activity. Although cell viability was unaffected, cellular metabolism was inhibited. Electron microscopy revealed evidence of lipid vacuolization, macroautophagy and myelin figure formation in cells cultured with either Pb or LPS. Confocal microscopy with antibodies against LC3B showed a punctate pattern consistent with the presence of mature autophagosomes. Collectively, these data suggest that 2.5–5.0μM Pb increased MHC-II surface expression by inhibiting metabolic activity, inducing autophagy, and increasing MHC-II trafficking in a macrophage cell line.