Grantee Research Project Results

2001 Progress Report: Immunotoxicity of Both Nondegraded and Biodegraded Polychlorinated Biphenyls (PCBs)

EPA Grant Number: R826687
Title: Immunotoxicity of Both Nondegraded and Biodegraded Polychlorinated Biphenyls (PCBs)
Investigators: London, Lucille
Current Investigators: London, Lucille , Smithwick, Laura Ashley , Quensen, John , Morris, Pamela
Institution: Medical University of South Carolina
EPA Project Officer: Aja, Hayley
Project Period: September 15, 1998 through September 14, 2001
Project Period Covered by this Report: September 15, 2000 through September 14, 2001
Project Amount: $379,176
RFA: Exploratory Research - Human Health (1998) RFA Text |  Recipients Lists
Research Category: Human Health

Objective:

The long-term goal of this research project is to understand the biological process by which complex mixtures of contaminants can be degraded in the environment and to apply that knowledge to better understand potential human health effects associated with exposure. We have focused on the anaerobic dechlorination and aerobic biodegradation polychlorinated biphenyls (PCBs) and their subsequent immunotoxicological effects. The persistence of PCBs in the environment and their bioaccumulation in living organisms raises concerns regarding their immunotoxic potential and subsequent effects on health. This study will examine the immunotoxicity of: (1) parent PCBs (either individual congeners or Aroclor mixtures); (2) anaerobic dechlorination of Aroclor mixtures; (3) aerobic biodegradation of Aroclor mixtures; and (4) chemical fractionation of each of the above PCB mixtures. The mouse B cell proliferative response to the mitogen, lipopolysaccaride (LPS), which is a well-defined immunologic parameter, will be used as an indicator of immunotoxicity. We also will investigate the ability of PCBs and their biodegraded/dechlorinated products to modulate immunoglobulin secretion in vitro after LPS stimulation.

Progress Summary:

In initial studies, four commercial PCB mixtures (Aroclors), selected individual noncoplanar congeners, or two tertiary mixtures containing one congener from each class significantly decreased the in vitro LPS-induced proliferation of mouse splenocytes. In contrast, selected individual coplanar or mono-ortho-coplanar congeners did not inhibit splenocyte proliferation or viability at any concentration. These results suggest that mixtures of PCBs and/or congener class (specifically, noncoplanar congeners) may be more highly immunotoxic than individual planar or mono-ortho-coplanar congeners alone. This is significant because PCB mixtures, not individual congeners, were used industrially and now contaminate the environment. In addition, with respect to human toxicity, only those congeners that bioaccumulate have the potential to influence human health. Our results implicating noncoplanar congeners as potentially immunotoxic are significant because these congeners selectively bioaccumulate, and traditional means of assessing toxicity based on TEQ values may underestimate their importance. We have observed significant inhibition of LPS-induced proliferation of splenocytes by a number of additional noncoplanar congeners, regardless of their chlorine content, that have been shown to bioaccumulate in human milk. Further, microbial reductive dechlorination of PCBs occurs in most PCB-contaminated anaerobic sedimentary environments. This process often results in the accumulation of ortho-substituted PCB congeners. Dechlorination of PCBs (Aroclors 1242, 1254, and 1260) by anaerobic sediments from the Cooper River (polluted) and three additional sites have been evaluated. Congener- specific analysis reveals specific meta- and paradechlorination. We have evaluated these anaerobically dechlorinated PCB mixtures for inhibition of LPS-induced proliferation. Because these cultures exhibit meta- and paradechlorination, the percentage of ortho congeners in these cultures is increasing. Our results indicate that these meta- and paradechlorinated samples were still highly toxic (inhibited LPS-induced proliferation), suggesting that the remaining ortho congeners contribute to toxicity. Second, a distinct difference was observed in the ability of these samples to inhibit Ig secretion independent of proliferation. The Hudson River and Raisin River samples that had similar dechlorination patterns as well as a similar inhibition of LPS- induced proliferation did not express a proliferation independent inhibition of Ig secretion. However, the Silver Lake sample that expressed a different dechlorination pattern also inhibited Ig secretion independent of proliferation.

To further investigate the selective toxicity associated with noncoplanar congeners, we have separated Aroclor 1242 into two fractions: (1) contains ortho substituted congeners; and (2) contains meta- and parasubstituted congeners. Only that fraction containing ortho substituted congeners inhibited LPS-induced proliferation. We have further refined this separation procedure to produce three fractions: Fraction 1: ortho substituted congeners, some mono-ortho congeners; Fraction 2: some mono-ortho congeners, non-ortho congeners, and polychlorinated napthalenes (PCNs); and Fraction 3: polychlorinated dibenzofurans (PCDFs) and polychlorinated dibenzo-p-dioxins (PCDD). Using these fractions, we can examine the contribution of ortho- and non-ortho substituted congeners as well as co-contaminants of Aroclors to the overall toxicity of the mixtures. We also will be able to employ this separation technique to dechlorinated PCB mixtures.

Finally, we have modified an in vitro culture system to investigate the effect of PCBs, both individual congeners and Aroclor mixtures, on the ability of pre-B cells to express surface immunoglobulin. We have optimized conditions for control induction of surface immunoglobulin by LPS in these cells and its detection by flow cytometry utilizing antibodies specific for both the kappa light chain and the IgM heavy chain. Two key results were obtained. First, Aroclor 1242 did not inhibit the induction of surface immunoglobulin on 70Z/3 cells. We are in the process of confirming these results with Aroclors 1260, 1254, 1242, and 1221. Second, at high Aroclor concentrations, significant cell death occurred. We have initiated experiments to evaluate whether PCB-induced death is through an apoptotic mechanism.

Future Activities:

The majority of this past year was spent developing large-scale anaerobic PCB dechlorinating cultures, which would generate samples with different PCB congener profiles. We plan on evaluating these cultures over the next year with a keen eye on the noncoplanar toxicity issue. Other activities will include the following:

1. We will continue to investigate the effect of anaerobic dechlorination of Aroclor mixtures with a keen eye on specific dechlorination patterns (ortho versus meta and para) and employ column chromatography methods to separate congener subclasses.

2. We will determine whether exposure to the various Aroclor mixtures (parent and modified) and various individual PCB congeners (coplanar, mono-ortho-coplanar, noncoplanar) modulate the ability of LPS-stimulated B cells to secrete immunoglobulin, the key function of B cells.

3. We will evaluate Aroclor mixtures (parent or modifed) as well as individual PCB congeners on the ability of a pre-B cell clone to express and secrete immunoglobulin after exposure. These experiments could lead to a more mechanistic analysis of the effect of PCBs on B cell function.

4. We will investigate induction of apoptosis on a pre-B cell clone after exposure to Aroclor mixtures (parent or modifed) as well as individual PCB congeners.

Journal Articles:

No journal articles submitted with this report: View all 14 publications for this project

Supplemental Keywords:

PCBs, soils and sediments, health effects, bioremediation, southeast., Health, RFA, Scientific Discipline, PHYSICAL ASPECTS, Waste, Health Risk Assessment, Physical Processes, Risk Assessments, chemical mixtures, Environmental Chemistry, Analytical Chemistry, Biochemistry, Bioremediation, environmental mutagens, detoxification, ecological risk assessment, aerobic degradation, immune response, human exposure, immune systems, PCB, in situ bioremediation, bioaccumulation, biodegradation, complex mixtures, exposure, bioacummulation, aroclor, lipopolysaccarid, human health risk

Progress and Final Reports:

Original Abstract

1999

2000 Progress Report

Final Report