Faculty Bibliography

This study describes the use of a panel of immune assays, originally developed by the National Toxicology Program for assessing xenobiotic-induced immunotoxicity in mice, to quantify the effects of sublethal malathion exposure on the immune responses of fish. For this study, Japanese medaka (Oryzias latipes) were exposed subchronically to the organophosphate pesticide malathion in a series of two experiments. In the first set of studies, fish were exposed for 7 or 14 d to untreated well water (i.e., controls) or to waterborne malathion at 0.2 or 0.8 mg/L. Following exposure, fish from each group were sacrificed and their kidneys (primary organ of leukopoiesis in fish and equivalent to mammalian bone marrow) were used to provide cells for assessing any malathion-induced effects upon nonspecific and acquired immune defense mechanisms. Effects upon humoral-mediated immunity were determined by enumerating antibody plaque-forming cell (PFC) numbers from a subset of fish exposed to malathion for 14 d and then injected intraperitoneally (ip) with sheep erythrocytes (sRBC). Results of these studies demonstrated that while malathion exposure had no significant effect upon hematocrit/leukocrit values or upon mitogen-stimulated T-cell lymphoproliferation, PFC numbers in the kidney of exposed fish were significantly reduced (compared to control fish) in a dose-dependent manner. In addition, total recoverable kidney cell numbers and viability, as well as superoxide anion production by kidney phagocytes, were reduced slightly (compared to control values) in fish exposed for 14 d to the highest malathion concentration tested. In the second set of experiments, medaka exposed for up to 21 d to either 0.1 or 0.3 mg malathion/L were challenged ip with an LD50 dose of the bacterial fish pathogen Yersinia ruckeri. Results from these infectivity studies demonstrated that exposure to either malathion concentration, for 14 or 21 d reduced host resistance against Yersinia infection. Taken together, these findings demonstrate the applicability of mammalian immune assays for predicting malathion-induced immunosuppression in a teleost fish, as well as the potential utility of a small laboratory fish to serve as an alternate model for mammals in immunotoxicological studies

Soluble and insoluble hexavalent chromium (Cr6+) agents are concomitantly released with ozone (O3) during welding. Although pulmonary/immunologic implications from exposure to each agent individually have been investigated, the effects from simultaneous exposure, as occurs under actual working conditions, are unclear. To investigate immunomodulatory effects of inhaled Cr6+, F-344 rats were exposed for 5 h/day, 5 days/week for 2 or 4 weeks to atmospheres containing soluble potassium chromate (K2CrO4) or insoluble barium chromate (BaCrO4), each alone at 360 micrograms Cr/m3 or in combination with 0.3 ppm O3. One day after the final exposure, rats were euthanized, their lungs were lavaged, and pulmonary macrophages (PAM) were recovered for assessment of basal and inducible functions. Rats inhaling K2CrO4-containing atmospheres had greater levels of total recoverable cells, neutrophils, and monocytes in bronchopulmonary lavage compared to rats exposed to insoluble Cr6+ atmospheres, O3 alone, or air; these rats also had a reduced percentage of PAM, although total PAM levels remained unaffected. Although Cr exposure-related changes in PAM functionality were evident, any dependence upon Cr solubility was variable. K2CrO4-containing atmospheres modulated PAM-inducible interleukins-1 and -6, and tumor necrosis factor-alpha production to a greater degree than those containing BaCrO4. Conversely, BaCrO4-containing atmospheres affected PAM basal nitric oxide production and interferon-gamma-primed/zymosan-stimulated reactive oxygen intermediate production to a greater extent than did those containing K2CrO4. In none of the PAM assays did co-inhalation of O3 result in a modulation of the effects obtained with either Cr6+ compound itself. The results indicate that, while immunomodulatory effects of inhaled Cr6+ upon PAM are related to particle solubility, the co-inhalation of O3 apparently does not cause further modifications of the metal-induced effects.

Through the efforts of different laboratories, a battery of immunological assays is available to predict the immunotoxicity of xenobiotics. These assays, originally developed in rodents, have been adapted for use in a variety of animal species and are now used routinely in these models to assess the immunotoxicity of different chemical classes. For example, our laboratory has employed assays that measure antibody-forming cell response to T-dependent antigens, T- and B-cell lymphoproliferation, macrophage function, and host resistance against infectious bacteria to assess metal-induced immunotoxicity in laboratory-reared Japanese medaka (Oryzias latipes); immunologically-related assays measuring antioxidant activity have also been used in this capacity. Results of the aforementioned investigations have shown the usefulness of these endpoints to reliably demonstrate chemical-mediated immunotoxicity in teleost systems. Many of these same endpoints have also proved successful for predicting the immunotoxic effects of contaminated aquatic environments in feral fish populations. For example, smallmouth bass collected from a chlorinated hydrocarbon-contaminated site demonstrated significant changes in blood cell profiles and kidney phagocyte function compared to fish collected from a 'clean water' reference site. Some of these same immune parameters have also been used successfully to predict the immunotoxicity of polluted aquatic environments in feral populations of fish-eating birds and harbor seals. While interspecies extrapolation is difficult and should be approached with caution due to variables such as metabolism and pharmacokinetics, results from these studies demonstrate the usefulness of these immune assays to predict the immunomodulating effects of xenobiotics in fish and other wildlife species, as well as the applicability of fish to serve as additional/alternate animal models for mammalian species in immunotoxicological studies