Studying Immune Responses in the American Kestrel (Falco sparverius)

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The objectives of this study are to (1) investigate whether the immune system will respond to chemical stressors, such as new flame retardant compounds, and (2) determine if such chemical stressors influence white blood cells (WBC) responses after exposure to a viral pathogen mimicking bird flu.

Figure 1. The American kestrel, Falco sparverius

Figure 1. The American kestrel, Falco sparverius. Photo by USFWS digital library.

The Science Issue and Relevance: Landscape-level environmental changes induced by human activities have been linked to alterations in animal disease dynamics. Immunology, the study of the physiological mechanisms that animals use to defend their bodies against invasion by microbes, provides insight into animal responses to stressors. Generally, immune pathways are evolutionarily conserved, with humans showing the most diverse and refined pathways. Immunological responses in other animals, including birds, can sometimes be delineated using assays developed for humans. Bird species, such as long-distance migratory and predatory raptors (e.g., American kestrel, Falco sparverius), are a useful model that reflects ecosystem changes by virtue of its life history.

Methodology for Addressing the Issue: The objectives of this study are to (1) investigate whether the immune system will respond to chemical stressors, such as new flame retardant compounds, and (2) determine if such chemical stressors influence white blood cells (WBC) responses after exposure to a viral pathogen mimicking bird flu. For species other than chickens (Gallus gallus), modest specific information on immunological pathways exists for birds; the American kestrel was selected to explore the biomarker responses of immune status in a biologically realistic environmental scenario. Key proteins on WBC (e.g., CD4, specific to human T-helper cells) will be identified and quantified in unexposed hatchlings and those exposed to an organophosphorus flame retardant. Then, each group of kestrels will be challenged by a synthetic analog of viral double-stranded RNA polyinosinic:polycytidylic acid (poly I:C), a ligand that induces immune responses characteristic of those stimulated in viral infections. Blood will be collected in a blood stabilizer and overnighted to WARC; flow cytometry analyses will then be performed on live and fixed WBC. Possible reactions, including the enhancement or reduction in immune response, will be interpreted.

Figure 2. Hatchling American kestrels

Figure 2. Hatchling American kestrels.

Future Steps: WARC scientists will continue to collaborate with USGS-Patuxent in analyzing data on biological endpoints in morphology, development, and biochemistry. The information will be used by USEPA in their evaluation on the new flame retardant compounds; the data will be used in bird flu prevention studies with regards to potential vaccine administration using poly I:C.

 

 

 

 

 

 

 

 

 

Figure 3.  American kestrel white blood cells

Figure 3. American kestrel white blood cells (arrows) are isolated from whole blood by differential centrifugation.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 4. Flow cytometric dot plot

Figure 4. a) Flow cytometric dot plot showing isolated and gated (arrow) white blood cells (WBC) from an American kestrel hatchling after exposure to a flame retardant. Red blood cells at the origin are gated out of the analysis of the protein marker for T helper WBC. b) An analysis of the gated WBC stained for the CD4-fluorochrome marker indicating the presence of the immune cell type. Histogram overlays of the control isotype (red) and anti-CD4 fluorescence label (blue) allows for measuring the immune response by the cells analogous to chicken T helper cells.