The How, Why and When of Immunological Testing

In vitro suppression of thymocyte apoptosis by metal-rich complex environmental mixtures: potential role of zinc and cadmium excess

Excessive amounts of heavy metals (e.g. Zn, Cu, Mn, Cr) are accumulated in river bottom sediments (RBS), being available to humans and animals along food chains. Increased exposure of mammals to certain metals (Cr, Cu) induces immunosuppresion, due to DNA damage and decreased survival of lymphoid cells. By contrast, excess of Zn and Cd causes inhibition of apoptosis thus suggesting increased survival of genetically mutated cells and higher cancer risks in exposed populations. Rat thymic lymphocytes represent a well-established model for apoptosis testing. The primary goal of our study was to assess the degree of apoptosis modulation with a number of RBS extracts differing in their metal contents. A series of freshly deposited RBS was collected at nine sampling stations along the Elbe River. All sediments were rich in Fe, Mn and Zn. The contents of Cu, Cr, Ni, Cd, Hg, Pb and As were much lower and interrelated. The short-term cytotoxicity of aqueous sediment extracts was assessed, using the following criteria: total cell counts; incidence of apoptosis and necrosis (morphological detection by fluorescent microscopy); and nuclear chromatin decay (by DNA flow cytometry). RBS extracts produced both apoptosis and necrosis of thymocytes. High contents of zinc and other heavy metals in the samples correlated with decreased thymocyte apoptosis (r= -0.543 to -0.608, P <0.01). The rates of thymocyte damage showed a distinct dependence on the time and region of sampling. Apoptosis modulation was also tested with pure salts of Mn(II), Zn(II), Cu(II), Cr(III) and Cd(II), at the test concentrations of 1, 10 and 100 microM. Cu(II) and Cr(III) proved to induce marked dose-related apoptosis, whereas Zn(II) ions caused significant suppression of apoptosis. These effects were similar to those trends observed with metal-rich sediments. In the present study. DNA flow cytometry proved to be a less sensitive index of cell death than morphological assay of apoptosis and/or necrosis. In summary, inhibition of lymphocyte apoptosis by RBS extracts and pure metals is associated with excess of zinc and, probably, cadmium. The proposed model of lymphoid cell apoptosis is a promising tool for screening cytotoxic effects of complex environmental samples.

Dose-response relationships of cytotoxicity, PFC response and histology in the spleen in rats treated with alkylating agents

Our previous study revealed the appropriate conditions for the plaque- forming cell (PFC) assay in rats. Using this assay in the present study, dose-response relationships of cytotoxicity, PFC response and histology in the spleen were evaluated in rats receiving alkylating agents. Rats were given a single intravenous administration of cyclophosphamide (CY) at a dose of 3, 10 or 30 mg/kg. Spleen weights and cellularity were decreased in the rats treated with 30 mg/kg. Suppressed PFC response wes observed in the rats receiving 10 mg/kg or more. In the rats treated with CY at 1, 3 or 10 mg/kg for 7 days, spleen weights and cellularity and PFC response were reduced at doses of 3 mg/kg or more. Treatment with the other alkylating agents, however, had a different consequence. Namely, in the rats treated with nitromin once or for 7 days, spleen weights and cellularity were decreased at a dose lower than that causing a reduction in the PFC response. In the rats treated with melphalan or chlorambucil, the weights and cellularity of the spleen tended to be decreased at a dose lower than that suppressing the PFC response. Histologically, in the case of CY, the marginal zone was narrow with cellular depletion in the rates receiving 3 mg/kg, whereas little change was seen in the periarteriolar lymphoid sheath (PALS). At a dose of 10 mg/kg, the marginal zone was markedly atrophied and slight atrophy of the PALS was seen. On the other hand, in the rats treated with nitromin, a dose-related decrease in the size of the spleen was seen without changes in the tissue architecture. Melphalan caused atrophy of both the marginal zone and the PALS at a dose suppressing PFC response. Regarding the red pulp, the extramedullary hematopoiesis disappeared with melphalan and nitromin, but not with CY. These results indicate that the decreases in weights and cellularity and histological changes in the spleen caused by the alkylating agents are detectable at the dose suppressing PFC response except for CY, which has a marked immunosuppressive action. Furthermore, the observed histological findings in the spleen were characteristic of each alkylating agent.