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 a nd biochemical function. Although sensitivity of the immune system to chemi cal exposure has been documented in laboratory animal and wildlife species, little work has been conducted on feral wildlife populations inhabiting co ntaminated sites. Immune function was measured in populations of wild cotto n 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 immun e organ mass and cellularity, hematology, irt vivo hypersensitivity, macrop hage function, killer cell activity, and lymphoproliferative responsiveness . In vitro proliferation 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% hig her for cotton rats collected from contaminated than reference sites in Sep tember 1991 and September 1992, respectively. Likewise, Con A-induced proli feration of splenocytes ranged form 20 to 53% higher in animals collected f rom contaminated than reference sites in three of four collection periods. The percentage of splenocytes (mean +/- SE) staining positive for Con A rec eptors was lower on contaminated sites (73.7 +/- 1.2%) than reference sites (77.0 +/- 1.4%) in September 1991. Other measures of immune function inclu ding macrophage metabolism, hypersensitivity, blood cellularity, and mass a nd cellularity of immune organs varied between contaminated and reference s ites. (C) 1999 Academic Press.