Serum IgM levels against select marine bacteria in the Atlantic sharpnose shark ( Rhizoprionodon terraenovae) from three estuaries

The Atlantic sharpnose shark ( Rhizoprionodon terraenovae) is abundant and easily captured throughout the southeastern United States. Therefore this species serves as an ideal model for generating basic immunological reagents to establish baseline information regarding the immunophysiology of sharks in the wild, and for attempting to correlate shark immune responses to potential pathogens with the quality of the habitat in which they reside. Sharpnose shark serum IgM was purified over a protein-A column and used to generate mouse polyclonal anti-sera to develop indirect ELISAs for quantifying bacteria-specific IgM antibody titers against Vibrio anguillarium, Vibrio cholerae, Vibrio parahaemolyticus, Vibrio charchariae, Escherichia coli, Mycobacterium fortuitum, and Mycobacterium marinum. Serum samples from Atlantic sharpnose sharks were collected in Charleston, SC, Beaufort, SC, and New Brunswick, GA estuaries during the early summer, and again from Charleston, SC in the fall of the same year. Relative antibody titers against E. coli, V. anguillarium, and V. parahaemolyticus differed among the three sampling locations, suggesting differences in microbial abundance or immunological responses in sharks from three locations. Overall, antibody titers in Charleston, SC sharks increased between summer and fall. A combination of chronic exposure to specific bacteria and increased antibody responses due to elevated water temperatures are likely responsible for elevated specific IgM in these sharks sampled in the fall. To our knowledge, this is the first study to examine IgM responses in elasmobranchs collected directly from their habitat.