Half-Lives, Body Distribution and Lack of Interconversion of Serum 19S and 7S IgM of Sharks

Passive administration of radiolabeled purified proteins derived from nurse and lemon shark serum to the homologous species revealed that the serum 7S IgM is neither a precursor nor a degradation product of the 19S IgM. The studies also showed that the 19S IgM is predominantly intravascular, as is the IgM of higher vertebrates, whereas the 7S IgM is distributed both extracellularly and intravascularly, as is the IgG in higher species. The half-lives of the 7S and 19S IgM depend on the species of shark, but the half-life of 19S IgM is comparable to that of man. In order to maintain the relatively high serum concentrations of 7S and 19S IgM in the shark, the rate of synthesis of both of these molecules exceeds that of higher vertebrates and totals 100 to 150 mg/kg/day.