Abstract

The southern sea otter, Enhydra lutris nereis, is a "threatened population" under the U.S. Endangered Species Act of 1973. The population of 2,317 individuals continues to decline despite efforts by the U.S. Fish and Wildlife Service and state agencies to preserve and expand the numbers of this subspecies. High rates of death are in part due to pathogens that are common in the population but apparently have only recently caused severe mortality. A compromised immune system could partly contribute to mortality of southern sea otters. Therefore, the objective of this study was to develop an enzyme-linked immunosorbent assay (ELISA) to quantify antibodies, or immunoglobulins (Ig), in the sea otter. Southern sea otter IgG was purified from sera by means of caprylic acid/ammonium sulfate precipitation and affinity chromatography. Purified IgG was inoculated into BALB/c mice, a fusion between mouse spleen cells and mouse myeloma cells was performed, and resulting hybridomas were screened for the production of antibodies specific for sea otter IgG. Five monoclonal antibodies (mAb) specific for the IgG heavy chain from southern sea otters have been characterized. Two of these mAb were purified for use in a sandwich ELISA to obtain data on baseline levels of IgG in 38 healthy southern sea otters and 113 Alaskan sea otters. Mean serum IgG concentration differed significantly between Southern (9.52 mg/ml, n=9) and Alaskan (13.78 mg/ml, n=57) sub-adult sea otters. In other age classes, no significant differences in serum IgG concentrations were found between the two subspecies. Additional samples will be added to these baseline data. This ELISA may be useful as part of future studies to determine if the immune system of southern sea otters is compromised by pollutants, pathogens, or other stressors.

Acknowledgements

This work was supported by grants from the University of Wisconsin-La Crosse and the Zoological Society of Milwaukee County.