Echinoderm Immunology: Bacterial Clearance by the Sea Urchin Strongylocentrotus Purpuratus.

Characteristics of bacterial clearance were investigated in the purple sea urchin, Strongylocentrotus purpuratus (Echinodermata: Echinoidea). Primary clearance kinetics were determined for three bacteria, a marine Gram negative motile rod, a marine Gram positive non-motile rod, and a Gram negative freshwater fish pathogen, Aeromonas salmonicida. Clearance kinetics differed for each of the three bacteria. Secondary clearance rates were not significantly different from primary clearance rates for any of the three bacteria, regardless of the time interval between inoculations (9-21 days), implying a probable absence of immunologic memory. During primary clearance, total coelomocyte counts declined 93% by 90 min post injection. All four coelomocyte types declined, however the relative proportions of each type changed during the six-hour sampling period. In cell-free coelomic fluid, viable counts of marine bacteria declined, with different kinetics for the two species. Viable counts in sea water controls did not change. Declines in viable counts may be due to bactericidal activity and/or agglutination, although bacterial agglutination was not observed.