Measurement of serum immunoglobulin concentration in killer whales and sea otters by radial immunodiffusion

Killer whales and sea otters maintained in captivity are the subjects of routine health monitoring programs, and interest in immunologic studies in sea otters has been rising recently in response to potential impacts from infectious disease and environmental pollution on the threatened southern sea otter population. Development of species-specific reagents for immunologic studies in these two marine mammals is currently in its infancy. In this study, killer whale and sea otter immunoglobulin-specific polyclonal antibodies were generated, and used to develop tests for serum Ig concentration in the killer whale (Orcinus orca) and the southern (Enhydra lutris nereis) and northern sea otter (Enhydra lutris lutris). Killer whale serum IgG was purified using caprylic acid/ammonium sulfate precipitation. Sea otter plasma IgG was purified using protein-A-agarose. Polyclonal anti-Ig antisera were produced in rabbits, and specificity confirmed by immunoelectrophoresis. Radial immunodiffusion was used to measure Ig concentration in serum or plasma samples derived from 21 captive killer whales, 18 wild and 4 captive southern sea otters and 15 wild and 4 captive northern sea otters grouped by age. Mean killer whale serum Ig concentration (+/-95% confidence interval) ranged from 15.04 +/- 3.97 g/l for animals aged 0-5 years to 26.65 +/- 9.8 g/l for animals aged >10 years. Mean sea otter serum Ig concentration (+/-95% confidence interval) ranged from 28.39 +/- 11.00 g/l for southern sub-adults to 32.76 +/- 11.58 g/l for southern adults. No significant difference in serum Ig concentration was found between southern and northern sea otters. Serum Ig concentrations in two northern sea otter pups were low compared to those of adult sea otters. The two serum Ig quantitation assays produced were highly specific and reproducible and will be useful additions to the limited number of tests available for immune function in these marine mammal species.