Acute Respiratory Exposure of Human Volunteers to Octamethylcyclotetrasiloxane (D4): Absence of Immunological Effects

Abstract Humans are exposed to silicones in a number of commercial and consumer products. Some of these silicones, including octamethycyclotetrasiloxane (D 4 ), are volatile. Therefore, there is a potential for respiratory exposure. A pharmacokinetic analysis of respiratory exposure to D 4 is presented in the accompanying paper (M. J. Utell et al., 1998, Toxicol. Sci. 44, 206–213). Possible immune effects of respiratory exposure to D 4 are investigated in this paper. Normal volunteers were exposed to 10 ppm D 4 or air for 1 h via a mouthpiece using a double-blind, crossover study design. Assays were chosen to screen for immunotoxicity or a systemic inflammatory response. Assessment of immunotoxicity included enumeration of peripheral lymphocyte subsets and functional assays using peripheral blood mononuclear cells. Because in humans there is no direct test for adjuvant effect of respiratory exposure, we analyzed proinflammatory cytokines and acute-phase reactants in peripheral blood, markers for a systemic inflammatory response, as surrogate markers for adjuvancy. These tests were repeated when the volunteers were reexposed to D 4 approximately 3 months after this initial exposure. Blood was obtained prior to exposure, immediately postexposure, and 6 and 24 h postexposure. In these short-term, controlled human exposures, no immunotoxic or proinflammatory effects of respiratory exposure to D 4 were found.