Inhibition of in vitro cytokine production by human peripheral blood mononuclear cells treated with xenobiotics: implications for the prediction of general toxicity and immunotoxicity.

The use of human peripheral blood mononuclear cells (PBMC) as an in vitro system to predict in vivo toxicity was investigated. For 58 chemicals, the effect on cytokine secretion (IL-5, IFNgamma and TNFalpha) by phytohaemagglutinin-activated PBMC was measured, IC50 values were calculated and correlations of these endpoints with human LC50 values were determined. The best result was obtained with IFNgamma as an endpoint for which the calculated R(2) value was 0.58 which is comparable with the R(2) values for the classical neutral red uptake (NRU) assays using murine 3T3 cells and normal human keratinocytes (R(2)=0.56 and 0.59, respectively). When for each chemical the lowest IC50 value of the three endpoints was correlated with LC50 the calculated R(2) increased slightly to 0.63. A specific strength of our test is that it corrects several outliers (diazepam, digoxin, malathion and verapamil hydrochloride) which do not fit in the linear regression analysis for IC50 values obtained with the classical 3T3 NRU assay. Furthermore, 2,4-dichlorophenoxyacetic acid, cyclosporine A and pentachlorophenol had a 10 times lower IC50 value than the estimated human LC50 value and were identified as immunotoxic alerts. In conclusion, new endpoints investigated in this study contribute to the prediction of immunotoxic effects and correct outliers of classical cytotoxicity assays.

Limited effect of selected organic pollutants on cytokine production by peripheral blood leukocytes.

To test the hypothesis that some persistent organic pollutants contribute to the increased prevalence of allergic disease, the effects of selected compounds on cytokine production by PBMC from control and allergic donors were evaluated. Cells were cultured for six days in the presence of a xenobiotic (PCB 153, hexachlorobenzene, pentachlorobenzene, pentachlorophenol, lindane, atrazine or DMSO vehicle) with phytohemagglutinin (PHA) or Dermatophagoides pteronyssinus extract, then for one day in the presence of PHA + phorbol 12-myristate 13-acetate. PCB 153 reduced the levels of IL-10, IFN-gamma and TNF-alpha. Hexachlorobenzene reduced the levels of IL-5, IL-10 and IFN-gamma. Pentachlorobenzene reduced IL-6 levels. Pentachlorophenol reduced IL-5 levels. Lindane and atrazine reduced both IL-5 and IFN-gamma. In addition, lindane reduced TNF-alpha levels. As these compounds had similar effects on cells from allergic and non-allergic donors, and as these effects were, in all cases, very limited indeed, the potential deleterious impact of the xenobiotics tested on the allergic response seems unlikely.

Inhibition of cytokine production by the herbicide atrazine. Search for nuclear receptor targets.

The hematological toxicity of the commonly used triazine herbicides is a cause for concern. In a search for molecular targets of these compounds, as their effects paralleled those seen with dexamethasone (DEX), we first looked for interaction with the glucocorticoid receptor. In contrast to the effects on proliferation and cytokine production of DEX, those induced by atrazine were not prevented by the glucocorticoid antagonist RU486. Also, whereas DEX was able to inhibit the promoter activity of genes regulated by NF-kappaB, atrazine failed to do so. We next looked for interaction with members of the peroxisome proliferator-activated receptor (PPAR) family. No peroxisome proliferation was observed in the liver or kidneys of mice treated with atrazine. Moreover, no PPAR-mediated induction of promoter activity was seen on targets of PPARalpha, PPARgamma, or PPARdelta. Similarly, neither atrazine nor simazine were able to stimulate RORalpha-mediated promoter activity. Finally, no binding of atrazine to the AR was observed. In conclusion, the effects of atrazine-type herbicides most probably do not result from interaction with the above-mentioned nuclear receptors.