Quantifying Circulating IgY Antibody Responses against Select Opportunistic Bacterial Pathogens and Correlations with Body Condition Factors in Wild American Alligators, Alligator mississippiensis.

Bailey M Alston,John A Bowden,Charles D Rice,Thomas R Rainwater,Benjamin B Parrott,Philip M Wilkinson

doi:10.3390/biology11020269

Bailey M Alston, John A Bowden + Show 4 more

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https://doi.org/10.3390/biology11020269

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Abstract

Simple SummaryImmunoglobulin Y (IgY) was purified from American alligator, Alligator mississippiensis, serum and used to develop a monoclonal antibody (mAb AMY-9) specific for the heavy chains of IgY. This antibody tool was then used to develop an ELISA for quantifying serum antibody responses against whole bacterial pathogens in alligators sampled in Florida, USA and South Carolina, USA. Antibody responses against some of the bacteria were very robust and varied by location and year, and in general these antibody responses correlated well with body condition factors, such as body-mass-indices (BMI). A novel mAb is now available to the scientific community interested in disease ecology of alligators.Little is known about the disease ecology of American alligators (Alligator mississippiensis), and especially how they respond immunologically to emerging infectious diseases and zoonotic pathogens. In this study, we examined serum samples collected from wild alligators in Florida (2010–2011) and South Carolina (2011–2012, 2014–2017) for antibody responses to multiple bacteria. Immunoglobulin Y (IgY) was purified from serum to generate a mouse monoclonal antibody (mAb AMY-9) specific to the IgY heavy chain. An indirect ELISA was then developed for quantifying antibody responses against whole cell Escherichia coli, Vibrio parahaemolyticus, Vibrio vulnificus, Mycobacterium fortuitum, Erysipelothrix rhusiopthiae, and Streptococcus agalactiae. In Florida samples the primary differences in antibody levels were between January–March and late spring through summer and early fall (May-October), most likely reflecting seasonal influences in immune responses. Of note, differences over the months in antibody responses were confined to M. fortuitum, E. rhusiopthiae, V. vulnificus, and E. coli. Robust antibody responses in SC samples were observed in 2011, 2014, and 2015 against each bacterium except E. coli. All antibody responses were low in 2016 and 2017. Some of the highest antibody responses were against V. parahaemolyticus, M. fortuitum, and E. rhusiopthiae. One SC alligator estimated to be 70+ years old exhibited the highest measured antibody response against V. parahaemolyticus and M. fortuitum. By combining data from both sites, we show a clear correlation between body-mass-indices (BMI) and antibody titers in all six of the bacteria examined. Our study provides a critical antibody reagent and a proof-of-concept approach for studying the disease ecology of alligators in both the wild and in captivity.

Highlights

The American alligator, Alligator mississippiensis, is a crocodilian distributed throughout the Southeastern USA, from Texas to North Carolina [1]
Efforts to develop and characterize a monoclonal antibody (mAb) against alligator Immunoglobulin Y (IgY) were successful in that mAb AMY-9 reacted against the 65 kDa heavy chain of IgY in both purified and whole serum samples, indicating high specificity for epitopes located on the heavy chain not shared with the truncated form and light chain (Figure 1B)
Future studies will focus on viral pathogens, but we demonstrate that circulating alligator IgY is specific for various bacterial proteins, and antibody levels against whole bacteria protein antigens are robust and may vary by location, year of sampling, time of year of sampling, and relative BMI

Summary

Introduction

The American alligator, Alligator mississippiensis, is a crocodilian distributed throughout the Southeastern USA, from Texas to North Carolina [1]. (a precursor to the Endangered Species Act of 1973), and thereafter removed from the list in 1987 as populations recovered [2,3]. Alligators are categorized as a species of Least Concern by the International Union for Conservation of Nature [4], populations remain vulnerable to multiple conservation threats including habitat degradation, pollution, invasive species, and climate change [5]. Reproductive traits of alligators are key factors in the ability of these animals to withstand environmental stressors, and healthy habitat and adaptability to changing environmental factors are essential to reproductive success [6–8]. The crocodilian immune system is impacted by environmental stressors (e.g., pathogens), and a healthy immune system is a key measure of fitness in terms of ecological and evolutionary success [9–11]. While most aspects of innate immunity, including biochemical and cellular components are conserved across all vertebrates, much less is known about pathogen-specific immune responses in reptiles [14,15], crocodilians

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