Proliferative Responses of Harbor Seal (Phoca vitulina) T Lymphocytes to Model Marine Pollutants

Abstract

In recent years, population declines related to viral outbreaks in marine mammals have been associated with polluted coastal waters and high tissue concentrations of certain persistent, lipophilic contaminants. Such observations suggest a contributing role of contaminant-induced suppression of cell-mediated immunity leading to decreased host resistance. Here, we assessed the effects of the prototypic polycyclic aromatic hydrocarbon (PAH), benzo [a]pyrene (B[a]P), and two polychlorinated biphenyls (PCBs), CB-156 and CB-80, on the T-cell proliferative response to mitogen in harbor seal peripheral lymphocytes. Despite the variability associated with our samples from free-ranging harbor seals, we observed a clear suppressive effect of B[a]P (10 uM) exposure on T cell mitogenesis. Exposures to 10 uM CB-156 and CB-80, and 1.0 and 0.1 uM B[a]P, did not produce significant depression in lymphoproliferation. Exposure to the model PAH at 10 uM resulted in a 61% (range 34 -97%) average reduction in lymphoproliferation. We were able to rule out a direct cytotoxic effect of B[a]P, indicating that observed effects were due to altered T cell function. Based on our in vitro results, we hypothesize that extensive accumulation of PAH by top-trophic-level marine mammals could alter T cell activation in vivo and impaired cell-mediated immunity against viral pathogens.Keywords: Benzo[a]pyrene; Harbor seal; Immunotoxicity; Lymphoproliferation; PAH; PCB INTRODUCTIONUnderstanding immune alterations related to environmental contamination has become an important priority in marine mammal research because of the high incidence in recent years of mass mortality events, unexplained population declines, and strandings among marine mammal populations (Dietz et al., 1989; Marine Mammal Commission, 1999;Kennedy et al., 2000). These events have been largely attributed to disease outbreaks caused by established or newly identified members of the genus Morbillivirus (Geraci et al., 1982;Osterhaus and Vedder, 1988;Duignan et al., 1995). Common features of these massive die-offs include highly polluted habitat and high tissue concentrations in affected individuals of persistent, lipophilic contaminants, including those known to have deleterious effects on the immune systems of rodents and humans (Hall et al., 1992;Visser et al., 1993;Reijnders, 1994). Whereas contaminant-induced immune suppression has been suggested as a major contributing factor in marine mammal disease epizootics, causal relationships and potential mechanisms of immunotoxicity have not been established (Olsson et al., 1994; Marine Mammal Commission, 1999;van Loveren et al., 2000).The harbor seal (Phoca vitulina) is an ideal model organism for investigating contaminant-induced immune alterations in marine mammals. Fish-eating seals are longlived, maintain large adipose deposits, and occupy high trophic levels in the marine food chain, thus accumulating relatively high levels of lipophilic contaminants (Boon et al., 1987;Young et al., 1998; Neale, unpublished data). Among marine m...

Contaminant Loads And Hematological Correlates In The Harbor Seal (Phoca vitulina) Of San Francisco Bay, California

“…If such factors covaried with contaminant levels, it would not be possible to distinguish their relative contributions or causal proximity to alterations in hematological parameters. Other environmental contaminants also were present in SFB, such as polycyclic aromatic hydrocarbons and heavy metals, which could affect immune function and blood values in these seals (Turk & Casteel, 1997;Neale et al, 2002).…”

“…Organochlorines such as polychlorinated biphenyls (PCBs) and DDT and its metabolites are ubiquitous environmental contaminants and are associated with various physiological disorders, such as impaired immunological function and reproductive success in harbor seals (Reijnders, 1980(Reijnders, , 1986Ross et al, 1996), decreased circulating vitamin A and thyroid hormone levels in juvenile habor and gray (Halichoerus grypus) seals (Brouwer et al, 1989;Jenssen et al, 2003), depressed humoral immune responses in northern fur seal (Callorhinus ursinus) pups (Beckmen et al, 2003), and decreased lymphocyte responses in bottlenose dolphin (Tursiops truncatus; Lahvis et al, 1995). In addition, Neale et al (2002) found that model PCBs depressed proliferation of harbor seal T lymphocytes in vitro. Brominated flame retardants are a novel class of environmental contaminants; within this group, the polybrominated diphenyl ethers (PBDEs) are currently used in large quantities, disperse similarly to PCBs and DDT, and bioaccumulate and biomagnify (Sellstrom et al, 1993;Meerts et al, 2001).…”

PAH‐ and PCB‐induced Alterations of Protein Tyrosine Kinase and Cytokine Gene Transcription in Harbor Seal (Phoca Vitulina) PBMC

“…Activation of T lymphocytes via T cell receptor (TCR) signaling begins with protein tyrosine kinase (PTK) activation, which initiates a cascade of intracellular signaling that transfers the signal to other molecules and eventually carries it to the nucleus, where gene transcription for the production of cytokines and other mediators of lymphocyte function occurs (a very similar process occurs in B cells). Previously, we demonstrated that certain PCB and PAH compounds suppressed in vitro mitogen-stimulated T cell proliferation in the harbor seal (Neale et al 2002). To explore potential mechanisms of this effect, here we exposed harbor seal leukocytes to the prototypic immunotoxic PAH, benzo[a ]pyrene (BaP), and 3,3 0 ,4,4 0 ,5,5 0 -hexachlorobiphenyl (CB-169), a model immunotoxic PCB, in vitro, and examined, via realtime PCR, the relative expression of certain genes important in T cell activation and function.…”

Dynamics of Vibrio with Virulence Genes Detected in Pacific Harbor Seals (Phoca vitulina richardii) Off California: Implications for Marine Mammal Health

“…Seals suffering from contaminant burden also may become immuno-compromised, therefore, more susceptible to virulent pathogens [53,61].…”