Indicators of Immunotoxicity in Populations of Cotton Rats (Sigmodon hispidus) Inhabiting an Abandoned Oil Refinery

Wildlife species inhabiting contaminated sites are often exposed to complex mixtures of chemicals, many of which have known effects on physiological and biochemical function. Although sensitivity of the immune system to chemical exposure has been documented in laboratory animal and wildlife species, little work has been conducted on feral wildlife populations inhabiting contaminated sites. Immune function was measured in populations of wild cotton rats (Sigmodon hispidus) inhabiting replicated reference and contaminated study sites at an abandoned oil refinery in Oklahoma four times from 1991 to 1992. Several measures of immunocompetence were examined including immune organ mass and cellularity, hematology,in vivohypersensitivity, macrophage function, killer cell activity, and lymphoproliferative responsiveness.In vitroproliferation of splenocytes, either spontaneous or induced with concanavalin A (Con A), was the most consistent and reliable indicator of immunotoxicity. Spontaneous proliferation of splenocytes was 48 and 24% higher for cotton rats collected from contaminated than reference sites in September 1991 and September 1992, respectively. Likewise, Con A-induced proliferation of splenocytes ranged form 20 to 53% higher in animals collected from contaminated than reference sites in three of four collection periods. The percentage of splenocytes (mean±SE) staining positive for Con A receptors was lower on contaminated sites (73.7±1.2%) than reference sites (77.0±1.4%) in September 1991. Other measures of immune function including macrophage metabolism, hypersensitivity, blood cellularity, and mass and cellularity of immune organs varied between contaminated and reference sites.