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Modulation of immune responses in mice by d-limonene.

The immunotoxicologic effects of d-limonene were determined. This naturally occurring substance is widely used in food flavorings and is a common additive in cosmetics. In the present study, BALB/c mice were treated with d-limonene for 9 wk. Effects on T- and B-cell responses were determined after 4 and 8 wk of treatment. Concanavalin-A responses at 8 wk, but not 4 wk, were suppressed in treated mice. A similar trend was observed for phytohemagglutinin and lipopolysaccharide responses. Evidence was presented that d-limonene had polyclonal activator action. Mice primed with keyhole limpet hemocyanin (KLH) prior to initiation of d-limonene treatment had suppressed primary and secondary anti-KLH responses. Mice treated with d-limonene prior to KLH priming produced significant increased antibody responses. Additional evidence for polyclonal stimulation was obtained by histopathologic examination of secondary lymphoreticular tissue. Significant secondary follicle development and prominent lymphoid nodules and aggregates were found in the pancreas and intestinal mucosa, particularly apparent in mice receiving the highest d-limonene dosage. A subchronic LD50 study was conducted wherein BALB/c mice received 16 daily doses of d-limonene. An LD50 of approximately 0.0850 mg d-limonene/kg (corrected for 82% purity) was determined.