Monocyte-macrophage system and polymorphonuclear leukocytes in workers exposed to low levels of metallic mercury

Our previous research (Soleo L, Vacca A, Vimercati L et al. Occup Environ M ed 1997;54:437-442) showed a reduction in tumor necrosis factor-alpha (TNF- alpha) serum levels in workers with prolonged exposure to low doses of inor ganic mercury, suggesting an in vivo functional defect of the monocyte-macr ophage system. On this basis, here we wondered whether workers exposed to l ower doses of metallic mercury displayed possible changes in the monocyte-m acrophage system. In this particular cohort of workers, we also sought for the effects of the exposure on the polymorphonuclear leukocytes (PMNL) chem otaxis. The monocyte-macrophage system and the natural killer (NK) cells we re examined in 19 exposed workers and in 25 unexposed workers, as the contr ol group (controls). Specifically, the circulating monocyte-macrophage cell s and their CD13, CD15 and CD33 subsets, serum cytokines (IL-8, GM-CSF and TNF-or) and the NK cells were analyzed. In seven exposed and seven controls randomly chosen workers the PMNL chemotaxis was also assessed. The selecte d indicator of mercury exposure were the levels of mercury in the urine (U- Hg), that was significantly higher in exposed workers than the controls (9. 7 +/-5.5 mug/l and 2.4 +/-1.2 mug/l, respectively). None of the exposed wor kers had shown signs of either acute or chronic inorganic mercury toxicity or any form of hypersensitivity. Several immunological variables tested, mo nocyte-macrophage cells and their subsets, NK cells and serum cytokines ove rlapped between the exposed and the control workers. When the workers were considered as a whole (exposed plus controls), no correlation was found bet ween current U-Hg and all immunological parameters. However, when exposed w orkers were studied separately, an inverse correlation was disclosed betwee n cumulative U-Hg and cells las percentage) expressing the CD13 (r = -0.599 ; P = 0.007) and CD15 (r = - 0.614; P = 0.005) molecules, and NK cells (r = - 0.455; P = 0.05). Moreover, a significant impairment in the PMNL chemota xis (t = 3.70; P = 0.003) was observed in the exposed workers. The results of our study suggest that the exposure to very low levels of metallic mercu ry led to subtle impairment of circulating monocyte and NK cells las percen tages) according to the increase in U-Hg levels, as well as of the PMNL che motactic function in this particular group of workers, even though they rem ain clinically asymptomatic. Therefore, we suggest that impairment of these parameters provide a sensitive indicator of metallic mercury and other che mical contaminants present in the environment. (C) 2001 Elsevier Science B. V. All rights reserved.