Cetacean immunology continues to be one aspect of marine mammal health in which little is known. While researchers have made great strides in characterizing acquired immunity, the lack of diagnostic tools available to marine mammal veterinarians continues to lag behind that of other species. Understanding cetacean immune function is critical in the diagnosis, treatment, and management of diseases in both free-ranging and collection dolphin populations. By establishing and comparing immune function of free-ranging and managed collection populations, researchers and veterinarians can evaluate the effects of age, housing (collection vs. free-ranging), infectious diseases, toxin exposure, and other factors on immune function among distinct populations.
In order to gain further insight into cetacean immunology, we recently developed an assay to quantify bottlenose dolphin immunoglobulin G (IgG), a predominant antibody sub-class of the humoral immune system. The enzyme-linked immunosorbent assay (ELISA) was used to establish reference ranges in 3 separate populations of bottlenose dolphins. It also allowed us to compare IgG levels between age groups, sex, and different housing conditions. Results showed that free-ranging Sarasota Bay bottlenose dolphins had significantly higher mean circulating IgG levels (9.1 mg/ml) when compared to 2 separate managed collection populations housed in closed pool systems (5.7 mg/ml) and open bay netted enclosures (6.2 mg/ml). When comparing complete blood cell count variables to IgG concentrations in serum, total white blood cell counts and eosinophil counts were the best predictors of IgG levels. This finding suggests that higher IgG levels in free-ranging dolphins are most likely attributable to a higher internal parasitic load. Dolphins in managed collections are fed frozen-thawed high-quality fish and are routinely treated with anti-parasite medications, where their free-ranging counterparts are not. These differences between populations emphasize the importance for establishing specific population reference ranges for immune function evaluation and overall health assessment.
Other applications for quantifying circulating IgG in dolphin serum, include its use in diagnosing immune disorders, such as agammaglobulinemia, immunosuppression or stimulation from drug therapy or infectious diseases, and disease syndromes associated with monoclonal gammopathies. The assay has also been used to quantify IgG in bottlenose dolphin colostrum and milk, and in diagnosing failure of passive transfer in neonates. An estimate of the onset of actively acquire humoral immunity in neonates can thus be established, along with recommendations for treatment of failure of passive transfer in both managed collections and stranded free-ranging dolphins.
Funding for the IgG project was provided by Merck Merial Veterinary Scholars.