Chromium in stainless steel welding fume suppresses lung defense responses against bacterial infection in rats

Pulmonary infections have been reported to be increased in welders. Previous animal studies have indicated that manual metal arc, stainless steel welding fume(MMA-SS) increased susceptibility to lung infections. MMA-SS is composed of a complex of metals (e.g., iron, chromium, nickel). The objective was to determine which metal component of MMA-SS welding fume alters lung defense responses. At Day 0, rats were intratracheally instilled one time with saline or MMA-SS at a concentration of 2 mg/rat. Additional rats were treated with the metal constituents, Fe2O3, NiO, or Cr2Na2O7 alone or in combination, at concentrations that are present in the dose used for MMA-SS treatment. At Day 3, rats were intratracheally inoculated with 5 x 103 Listeria monocytogenes. At Days 6, 8 and 10, homogenized left lungs were cultured, and colony-forming units were counted after an overnight incubation to assess pulmonary bacterial clearance. At Day 3 (prior to infection) and at Days 6, 8 and 10, right lungs were lavaged to recover cells and fluid from the airspaces to measure lung injury, inflammation, and cytokine secretion. The production of reactive oxygen species by phagocytes recovered from the lungs was measured. Exposure to MMA-SS, soluble Cr, or the mixture of all three metals before infection significantly increased bacterial lung burden and tissue damage when compared to control. Animals treated with NiO or Fe2O3 did not differ from control. Animals pre-treated with soluble Cr had alterations in inflammation and in the production of different cytokines (TNF alpha, IL-6, IL-2, and IL-12) involved in lung immune responses. This study indicates that soluble Cr present in MMA-SS is likely the primary component responsible for the suppression of lung defense responses associated with stainless steel welding fumes.