A simple assay for measurement of ovotransferrin - a marker of inflammation and infection in birds

1. Ovotransferrin is an acute-phase protein with iron-binding and immunomodulatory functions. In poultry, ovotransferrin levels increase in response to inflammation or infection, but little is known about responses in wild bird species. 2. We present a simple assay for the determination of ovotransferrin-like activity in the plasma of wild birds. The assay uses very small sample volumes, works with previously frozen plasma, is inexpensive to run, and requires only standard laboratory equipment and a spectrophotometer. Importantly, the assay does not require species-specific antibodies, making it applicable to a wide variety of species and particularly useful in comparative studies of immune function. 3. We detected significant variation in ovotransferrin concentrations among 22 bird species. Ovotransferrin concentrations were significantly repeatable among individuals, and concentrations increased significantly in response to a lipopolysaccharide challenge. 4. Within but not among species, concentrations of ovotransferrin were significantly and positively correlated with concentrations of haptoglobin, another acute-phase protein that also binds iron. Differences in concentrations of acute-phase proteins might reflect broader differences in immune strategies and responses to infection. Measuring ovotransferrin in addition to haptoglobin therefore provides fresh insights into differences in immunological defences among populations and species. 5. This assay will serve as a useful addition to the existing arsenal of field-friendly assays that have been developed for addressing questions in ecological immunology. 5. This assay will serve as a useful addition to the existing arsenal of field-friendly assays that have been developed for addressing questions in ecological immunology

Intense flight and endotoxin injection elicit similar effects on leukocyte distributions but dissimilar effects on plasma-based immunoplogical indices in pigeons

Most birds rely on flight for survival. Yet as an energetically taxing and physiologically integrative process, flight has many repercussions. Studying pigeons (Columba livia) and employing physiological and immunological indices that are relevant to ecologists working with wild birds, we determined what, if any, acute immune-like responses result from bouts of intense, non-migratory flight. We compared the effects of flight with the effects of a simulated bacterial infection. We also investigated indices in terms of their post-flight changes within individuals and their relationship with flight speed among individuals. Compared to un-flown controls, flown birds exhibited significant elevations in numbers of heterophils relative to numbers of lymphocytes and significant reductions in numbers of eosinophils and monocytes. Furthermore, within-individual changes in concentrations of an acute phase protein were greater in flown birds than in controls. However, none of the flight-affected indices showed any evidence of being related to flight speed. While some of the effects of flight were comparable to the effects of the simulated bacterial infection, other effects were observed only after one of these two physiological challenges. Our study suggests that flight by pigeons yields immune-like responses, and these responses have the potential to complicate the conclusions drawn by ecologists regarding immune function in free-living birds. Still, a better understanding of the repercussions of flight can help clarify the ties between the physiology of exercise and the disease ecology of migration and will ultimately assist in the broader goal of accounting for immunological variation within and among species

Baseline haptoglobin concentrations are repeatable and predictive of certain aspects of a subsequent experimentally-induced inflammatory response

Ecologists sometimes assume immunological indices reflect fundamental attributes of individuals—an important assumption if an index is to be interpreted in an evolutionary context since among-individual variation drives natural selection. Yet the extent to which individuals vary over different timescales is poorly understood. Haptoglobin, an acute phase protein, is an interesting parameter for studying variability as it is easily quantified and concentrations vary widely due to the molecule's role in inflammation, infection and trauma. We quantified haptoglobin in pigeon plasma samples collected over fourteen months and calculated repeatability to evaluate if haptoglobin concentration is a distinctive trait of individuals. We also explored the capacity of baseline haptoglobin concentrations to predict an array of physiological changes associated with a subsequent experimentally-induced inflammatory response. Maximum repeatability, which occurred over a short mid-winter interval, equaled 0.57. Baseline haptoglobin concentrations predicted response haptoglobin concentrations better than any other endotoxin-induced change. Overall, we identified several strengths and limitations of baseline [Hp] quantification. Acknowledging these qualities should lead to more refined conclusions in studies of the ecology and evolution of immune function

Seasonal patterns in immune indices reflect microbial loads on birds but not microbes in the wider environment

Documenting patterns in immune function is a first step to understanding immune variation, but to comprehend causes and consequences, antigen and parasite exposure that may drive such variation must be determined. We measured host-independent microbial exposure in five species of larks (Alaudidae) in the Arabian Desert by sampling ambient air for culturable microbes during late spring and winter, two periods with contrasting environmental conditions. We developed a novel technique to assay densities of microbes shed from birds, and we quantified four indices of constitutive innate immunity. Birds shed significantly more microbes during spring than winter, and all immune indices except one were also significantly higher during spring. In contrast, concentrations of airborne environmental microbes were higher in winter. Among all birds in both seasons, lysis titers were positively correlated with total densities of microbes shed from birds, suggesting that immune defenses are directed towards the microbes that birds carry, rather than microbes in the wider environment. Our findings highlight the relevance of quantifying non-specific immune challenges in ecological immunology studies, and reinforce the importance of both host-dependent and host-independent measures of antigenic pressure for understanding immune variation. Read More: http://www.esajournals.org/doi/abs/10.1890/ES11-00287.