Intracellular Cytopathic Effects of Marine Brucella on Beluga and Human Monocytes
IAAAM 2009
Cara L. Field1,2; Jennifer Higgins1; J. Lawrence Dunn1; Tracy Romano1
1Mystic Aquarium and Institute for Exploration, Mystic, CT, USA; 2University of Connecticut, Dept of Marine Sciences, Groton, CT, USA

Abstract

Marine Brucella species have been isolated from marine mammals worldwide; however, the pathogenicity of these marine species has not been characterized. Lesions attributed to marine Brucella include osteomyelitis, neurobrucellosis, and abortion, though Brucella has also been isolated from animals with no apparent lesions. Marine Brucella species are zoonotic as evidenced by four documented human cases. Terrestrial Brucella cause significant morbidity in host-adapted species, while non-host adapted species may either become chronically infected or clear the infection, depending in part on the lipopolysaccharide structure of the Brucella. Infection of mononuclear phagocytes occurs through lipid raft-mediated entry or phagocytosis, and the Brucella replicates intracellularly after attenuating the host cell response. We hypothesize that marine Brucella have a predilection for, and are phagocytosed preferentially by, marine mammal mononuclear phagocytic cells, and diminish host cell immune response by causing a reduction of respiratory burst activity. We further propose that human mononuclear phagocytes, as non-host adapted cells, will display a more robust response to infection than marine mammal mononuclear phagocytes.

Phagocytosis and respiratory burst activity of beluga and human monocytes and granulocytes were evaluated using flow cytometry. Whole blood was incubated with dichlorodihydrofluorescein diacetate (DCFDA), a marker of reactive oxygen species, and challenged with either Staphylococcus aureus or marine Brucella labeled with propidium iodide. Cellular response was evaluated over a 2 hour time course post-infection.

Beluga monocytes and granulocytes both phagocytosed large numbers of S. aureus. As is the case with terrestrial Brucella species, marine Brucella was phagocytosed primarily by monocytes, with minimal granulocyte response in comparison to S. aureus infection. As expected, respiratory burst activity was highest in beluga granulocytes infected with S. aureus, though Brucella-infected granulocytes also displayed a low level of respiratory burst activity. Monocyte respiratory burst response to Brucella was low, consistent with the proposed mechanism of reduced intracellular response to this pathogen. However monocyte respiratory burst response to S. aureus was also unexpectedly low, indicating either reduced intracellular response or an inability to properly detect the maximal host cell response.

Human monocytes and granulocytes both phagocytosed large amounts of Brucella as well as S. aureus, unlike beluga granulocytes which displayed a minimal phagocytic response to Brucella infection. Respiratory burst activity was again highest in human granulocytes infected with S. aureus. Human monocytes infected with S. aureus and granulocytes and monocytes infected with Brucella displayed minimal respiratory burst activity.

The above results support the hypothesis that beluga mononuclear phagocytic cells have a predilection for the phagocytosis of marine Brucella in comparison to granulocytes, though this response is not apparent for human granulocytes and monocytes. The differential respiratory burst response between monocytes and granulocytes in response to infection with S. aureus may be attributed to monocyte production of reactive oxygen species which may not be adequately measured by the fluorescent probe (DCFDA) used in these experiments. Studies are underway to evaluate cytokine production by human and beluga mononuclear phagocytes to further characterize the intracellular response to this pathogen.

Speaker Information
(click the speaker's name to view other papers and abstracts submitted by this speaker)

Cara L. Field
Mystic Aquarium and Institute for Exploration
Mystic, CT, USA


MAIN : Immunology : Marine Brucella
Powered By VIN

Friendly Reminder to Our Colleagues: Use of VIN content is limited to personal reference by VIN members. No portion of any VIN content may be copied or distributed without the expressed written permission of VIN.

Clinicians are reminded that you are ultimately responsible for the care of your patients. Any content that concerns treatment of your cases should be deemed recommendations by colleagues for you to consider in your case management decisions. Dosages should be confirmed prior to dispensing medications unfamiliar to you. To better understand the origins and logic behind these policies, and to discuss them with your colleagues, click here.

Images posted by VIN community members and displayed via VIN should not be considered of diagnostic quality and the ultimate interpretation of the images lies with the attending clinician. Suggestions, discussions and interpretation related to posted images are only that -- suggestions and recommendations which may be based upon less than diagnostic quality information.

CONTACT US

777 W. Covell Blvd., Davis, CA 95616

vingram@vin.com

PHONE

  • Toll Free: 800-700-4636
  • From UK: 01-45-222-6154
  • From anywhere: (1)-530-756-4881
  • From Australia: 02-6145-2357
SAID=27