Altered AP-1 (activating protein-1) activity and c-jun activation in T cells exposed to the amide class herbicide 3,4-dichloropropionanilide (DCPA)

The toxicity of the N-hydroxy and 6-hydroxy metabolites of 3,4-dichloropropionanilide does not depend on calcium release-activated calcium channel inhibition

Each year ~1 billion kg of herbicides are used worldwide to control the unwanted growth of plants. In the United States, over a quarter of a billion kg of herbicides are used, representing 28% of worldwide use. (Kiely, T., Donaldson, D., and Grube, A. [2004]. Pesticide Industry Sales and Usage. 2000 and 2001 Market Estimates. Available at: http://www.epa.gov/pesticides/pestsales/01pestsales/market_estimates2001.pdf. Accessed October 25, 2012.) Propanil (3,4-dichloropropionanilide [DCPA]) is a commonly used herbicide in the United States, with 2-4 million kg applied annually to 2 million acres of crop land. The immunomodulatory effects of DCPA have been well documented, but limited data are available on the effects of its metabolites. (Salazar, K. D., Ustyugova, I. V., Brundage, K. M., Barnett, J. B., and Schafer, R. [2008]. A review of the immunotoxicity of the pesticide 3,4-dichloropropionanalide. J. Toxicol. Environ. Health B Crit. Rev. 11, 630-645.) In mammals, hepatic enzymes metabolize DCPA, resulting in the production of 3,4-dichloroaniline (DCA). Further biotransformation of DCA leads to the production of 6-hydroxy-3,4-dichloroaniline (6OH-DCA) and N-hydroxy-3,4-dichloroaniline (NOH-DCA). We report, for the first time, the immunotoxic effects of DCPA metabolites on T-cell function. Human Jurkat T cells were exposed to varying concentrations of DCPA or its metabolites and assayed for effects on T-cell function. In addition, fluorine analogs of DCPA and DCA were investigated to determine the relative role of chlorine substituents on T-cell immunotoxicity. Here we report that exposure of Jurkat T cells to DCPA and DCA alters IL-2 secretion, nuclear factor of activated T cells (NFAT) activity, and calcium influx. However, exposure to 6OH-DCA and NOH-DCA reduces IL-2 secretion and NFAT activity but has no effect on calcium flux. When both chlorines in DCPA and DCA were substituted with fluorines all effects were abrogated. Our data indicate that metabolites of DCPA have differential effects on T-cell function and the presence of chlorines plays an important role in eliciting these effects.

Evaluating macrophages in immunotoxicity testing

Macrophages are the heterogeneous grouping of cells that are derived from monocytes. They have a multitude of functions depending on their final differentiated state. These functions range from phagocytosis to antigen presentation to bone destruction, to name a few. Their importance in both the innate and acquired immune functions is undeniable. Xenobiotics that degrade their functional status can have grave consequences. In this chapter, we provide an overview of the types of macrophages, their hematopoietic origin and a general discussion of the many different assays that are used to assess their functional status.

A review of the immunotoxicity of the pesticide 3,4-dichloropropionanalide

The pesticide 3,4-dichloropropionanilide (propanil or, alternatively, DCPA) is a member of the acetanilide chemical family and is predominantly used for the control of weeds on commercial rice crops worldwide. This article was written to provide a brief review of the general toxicity of propanil followed by a detailed summary of the immunotoxicity studies that were performed to date in mammalian in vivo and in vitro models. Propanil affects the immune system at organ, cellular, and molecular levels. Studies demonstrated that it produces thymic atrophy and splenomegaly and decreases developing T- and B-cell populations in the thymus and bone marrow. Natural killer (NK) cells and macrophages are critical components of the innate immune system. NK cell cytotoxicity and the ability of macrophages to phagocytose, kill pathogenic bacteria, and produce inflammatory cytokines are suppressed by propanil. Propanil also affects the respiratory burst of macrophages, inhibiting reactive oxygen and nitrogen species production. Molecular mechanisms responsible for propanil's effects have begun to be elucidated and include alterations in nuclear factor (NF)-kappaB transcription factor activity and intracellular Ca(2+) signaling. Propanil exposure alters a number of functions of mature T lymphocytes and B lymphocytes that impacts the adaptive immune response. T-cell cytotoxic activity and cytokine production are major T-cell functions inhibited by propanil. The humoral antibody response to model antigens and intact bacteria is differentially affected after propanil exposure. How these changes in innate and adaptive immune responses impact the host response to bacterial challenge or vaccination has begun to be examined.

3,4-Dichloropropionanilide (DCPA) inhibits T-cell activation by altering the intracellular calcium concentration following store depletion

Stimulation of T cells through the T-cell receptor results in the activation of a series of signaling pathways that leads to the secretion of interleukin (IL)-2 and cell proliferation. Influx of calcium (Ca(2+)) from the extracellular environment, following internal Ca(2+) store depletion, provides the elevated and sustained intracellular calcium concentration ([Ca(2+)](i)) critical for optimal T-cell activation. Our laboratory has documented that exposure to the herbicide 3,4-dichloropropionanilide (DCPA) inhibits intracellular signaling events that have one or more Ca(2+) dependent steps. Herein we report that DCPA attenuates the normal elevated and sustained [Ca(2+)](i) that follows internal store depletion in the human leukemic Jurkat T cell line and primary mouse T cells. DCPA did not alter the depletion of internal Ca(2+) stores when stimulated by anti-CD3 or thapsigargin demonstrating that early inositol 1,4,5-triphosphate-mediated signaling and depletion of Ca(2+) stores were unaffected. 2-Aminoethyldiphenol borate (2-APB) is known to alter the store-operated Ca(2+) (SOC) influx that follows Ca(2+) store depletion. Exposure of Jurkat cells to either DCPA or 50 microM 2-APB attenuated the increase in [Ca(2+)](i) following thapsigargin or anti-CD3 induced store depletion in a similar manner. At low concentrations, 2-APB enhances SOC influx but this enhancement is abrogated in the presence of DCPA. This alteration in [Ca(2+)](i), when exposed to DCPA, significantly reduces nuclear levels of nuclear factor of activated T cells (NFAT) and IL-2 secretion. The plasma membrane polarization profile is not altered by DCPA exposure. Taken together, these data indicate that DCPA inhibits T-cell activation by altering Ca(2+) homeostasis following store depletion.

Differential response of Mono Mac 6, BEAS-2B, and Jurkat cells to indoor dust

BACKGROUND

Airway toxicity of indoor dust is not sufficiently understood.

OBJECTIVES

Our goal in this study was to describe the effects of indoor dust on human monocyte, epithelial, and lymphocyte cell lines. We aimed to a) obtain a comprehensive and intelligible outline of the transcriptional response; b) correlate differential transcription with cellular protein secretion; c) identify cell line-specific features; and d) search for indoor dust-specific responses.

METHODS

Settled dust was sampled in 42 German households, and various contaminants were characterized. We exposed Mono Mac 6, BEAS-2B, and Jurkat cells to 500 microg/mL indoor dust for 6 hr. Outcome parameters included the transcriptional profile of an oligonucleotide microarray covering 1,232 genes. Significantly enriched Gene Ontology themes were calculated. Supernatant protein levels of 24 inflammatory response proteins served to confirm transcriptional results.

RESULTS

An intraclass correlation coefficient of 0.8 indicated reasonable microarray reproducibility. The transcriptional profile was characterized by enhancement of detoxification and a danger and defense response. Differential gene regulation correlated with protein secretion (Goodman and Kruskal's gamma coefficient: 0.72; p < 0.01). Mono Mac 6 cells revealed the highest fraction of differentially expressed genes, dominated by up-regulation of various cytokines and chemokines. BEAS-2B cells revealed weaker changes in a limited set of inflammatory response proteins. No significant changes were observed in Jurkat cells.

CONCLUSIONS

Monocytes are particularly responsive to indoor dust. We observed a classical T-helper 1-dominated immune response, which suggested that bioorganic contaminants are relevant effectors in indoor dust.