Association of occupational exposures with ex vivo functional immune response in workers handling carbon nanotubes and nanofibers

Abstract

The objective of this study was to evaluate the association between carbon nanotube and nanofiber (CNT/F) exposure and ex vivo responses of whole blood challenged with secondary stimulants, adjusting for potential confounders, in a cross-sectional study of 102 workers. Multi-day exposure was measured by CNT/F structure count (SC) and elemental carbon (EC) air concentrations. Demographic, lifestyle and other occupational covariate data were obtained via questionnaire. Whole blood collected from each participant was incubated for 18 hours with and without two microbial stimulants (lipopolysaccharide/LPS and staphylococcal enterotoxin type B/SEB) using TruCulture technology to evaluate immune cell activity. Following incubation, supernatants were preserved and analyzed for protein concentrations. The stimulant:null response ratio for each individual protein was analyzed using multiple linear regression, followed by principal component (PC) analysis to determine whether patterns of protein response were related to CNT/F exposure. Adjusting for confounders, CNT/F metrics (most strongly, the SC-based) were significantly (p < 0.05) inversely associated with stimulant:null ratios of several individual biomarkers: GM-CSF, IFN-γ, interleukin (IL)-2, IL-4, IL-5, IL-10, IL-17, and IL-23. CNT/F metrics were significantly inversely associated with PC1 (a weighted mean of most biomarkers, explaining 25% of the variance in the protein ratios) and PC2 (a biomarker contrast, explaining 14%). Among other occupational exposures, only solvent exposure was significant (inversely related to PC2). CNT/F exposure metrics were uniquely related to stimulant responses in challenged whole blood, illustrating reduced responsiveness to a secondary stimulus. This approach, if replicated in other exposed populations, may present a relatively sensitive method to evaluate human response to CNT/F or other occupational exposures.

Keywords: Carbon nanotubes; carbon nanofibers; epidemiology; immunosuppression; nanomaterials.

Fig. 1.

Spider plot of untransformed biomarker ratios by CNT structure count concentration tertile (TEM max). The radial axis of the plot represents the biomarker response (i.e., the mean value of stimulant:null ratios for the group of workers in each CNT exposure tertile), and the biomarkers are ordered by their mean biomarker response across the entire group of workers. * Untransformed biomarker ratio was significantly different among tertiles of exposure (p<0.05)

Fig. 2.

Heat map of the association of demographic, lifestyle, and occupational variables with transformed inflammatory biomarker response ratios.

Fig. 3.

Results of the comparative analysis for age, current solvent use (Sol-cur), and TEM-max. Comparative analysis of Diseases and Bio Functions considering all analytes (Fig. 3a) and only the analytes reaching significance at p<0.05 (Fig. 3b) were sorted in descending order from the most significant inverse association, represented by z-score, to TEM-max. Results of the specific analytes reaching significance for each measure and the interaction with TEM-max was represented in the Venn diagram (Fig. 3c).