Brucella pinnipedialis hooded seal (Cystophora cristata) strain in the mouse model following exposure to PCB 153

Summary

Brucella spp. have been isolated from and serologically indicated in marine mammals from most of the world, with an exceptionally high prevalence in the declined Northeast Atlantic population of hooded seals (Cystophora cristata), and Brucella pinnipedialis hooded seal strain is shown to differ from other pinniped brucellae. Hooded seal meat was distributed for human consumption in Norway until 2007 when the commercial hunt was stopped. Persistent organic pollutants accumulate in the Arctic and studies indicate that exposure to these compounds may lead to inadequate immune function and disease. PCB 153 is found at high levels in the Arctic, including in hooded seal. The goal of the study was to evaluate the pathogenesis of B. pinnipedialis hooded seal strain in the mouse model and investigate whether the course of infection and the immunological response was affected following exposure to PCB 153. BALB/c mice were inoculated intraperitoneally with B. pinnipedialis hooded seal strain or Brucella suis 1330 (positive control). Two of four groups of 20 mice were exposed to PCB 153 in the food (4.08 µg/g). Mice were killed at one, three, six and twelve weeks post infection (p.i.). The number of colony forming units (CFU) in spleen, liver and kidney was evaluated. The spleens were aseptically removed and splenocytes were cultured in vitro and stimulated with Concanavalin A. RNA was extracted and cDNA produced. We validated the housekeeping gene β-actin with the ΔΔCt-method for gene expression studies with qRT-PCR for the cytokines IL-4, IL-10 and IFN-γ. Sequencing of the PCR-products and BLAST analysis confirmed the identity of the cytokines. B. pinnipedialis hooded seal strain was able to establish an infection but at a lower level than B. suis 1330. The infection with B. pinnipedialis was cleared from all organs within twelve weeks p.i. Further, the level of anti-Brucella antibodies in the B. pinnipedialis infected mice never reached the same level as in the B. suis 1330 infected mice, and started declining after week six p.i., while the mice infected with B. suis 1330 had a high level of antibodies still at twelve weeks p.i. Exposure to PCB 153 did not alter the number of CFU or the level of anti-Brucella antibodies neither for the B. suis 1330 nor for B. pinnipedialis infected mice. Preliminary results have not yet confirmed a change in the immunological response between the PCB-exposed and non PCB-exposed groups. The results indicate that B. pinnipedialis hooded seal strain has a lower pathogenicity than B. suis 1330 in the mouse model. This might indicate that B. pinnipedialis infection is not responsible for the decline in the Northeast Atlantic population of hooded seals.