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Polyreactive antibodies are a major component of the natural antibody repertoire and are capable of binding a variety of structurally unrelated antigens. Many of the properties attributed to natural antibodies, in fact, are turning out to be due to polyreactive antibodies. In humans, each day, billions of cells undergo apoptosis. In the present experiments, we show by ImageStream technology that although polyreactive antibodies do not bind to live T cells they bind to both the plasma membrane and cytoplasm of late apoptotic cells, fix complement, generate the anaphylatoxin C5a and increase by as much as 5 fold complement-mediated phagocytosis by macrophages. Of particular importance, T cells undergoing apoptosis following infection with HIV also bind polyreactive antibodies and are phagocytosed. We conclude that the polyreactive antibodies in the natural antibody repertoire contribute in a major way to the clearance of cells made apoptotic by a variety of natural and infectious processes [ABSTRACT FROM AUTHOR]

• The macroalgae Saccharina latissima, Chondrus crispus, and Ulva reduced Alexandrium catenella densities by 60–80% in culture experiments. • In bottle and mesocosm experiments with bloom water, S. latissima and Ulva reduced Alexandrium catenella densities by 50–95%. • The sugar kelp, S. latissima , was capable of reducing the accumulation of saxitoxin in mussels below the US FDA closure limit for bivalves. • Allelochemicals were the most probable algacidal mechanism, although pH elevation, nutrient reduction, and macroalgae-attached bacteria may have also contributed in field-based experiments. • The aquaculture of seaweeds represents an environmentally friendly and potentially profit-generating measure to mitigate A. catenella -caused damage to the shellfish aquaculture and harvesting industries. Alexandrium catenella is a harmful algal bloom (HAB)-forming dinoflagellate that causes significant damage to the cultivation and harvest of shellfish due to its synthesis of paralytic shellfish toxins. To evaluate the potential for macroalgae aquaculture to mitigate A. catenella blooms, we determined the effects of three cultivable macroalgae - Saccharina latissima (sugar kelp) , Chondrus crispus (Irish moss) , and Ulva spp. - on A. catenella in culture- and field-based experiments. Co-culture growth assays of A. catenella exposed to environmentally realistic concentrations of each macroalgae showed that all species except low levels of C. crispus caused cell lysis and significant reductions in A. catenella densities relative to control treatments of 17–74% in 2–3 days and 42–96% in ~one week (p <0.05 for all assays). In a toxin accumulation experiment, S. latissima significantly lessened (p <0.05) saxitoxin (STX) accumulation in blue mussels (Mytilus edulis), keeping levels (71.80±1.98 µg STX 100 g−1) below US closure limits (80 µg STX 100 g−1) compared to the untreated control (93.47±8.11 µg STX 100 g−1). Bottle incubations of field-collected, bloom populations of A. catenella experienced significant reductions in cell densities of up to 95% when exposed to aquaculture concentrations of all three macroalgae (p <0.005 for all). The stocking of aquacultured S. latissima within mesocosms containing a bloom population of A. catenella (initial density: 3.2 × 104 cells L−1) reduced the population of A. catenella by 73% over 48 h (p <0.005) while Ulva addition caused a 54% reduction in A. catenella over 96 h (p <0.01). Among the three seaweeds, their ordered ability to inhibit A. catenella was S. latissima > Ulva spp. > C. crispus. Seaweeds' primary anti- A. catenella activity were allelopathic, while nutrient competition, pH elevation, and macroalgae-attached bacteria may have played a contributory role in some experiments. Collectively, these results suggest that the integration of macroalgae with shellfish-centric aquaculture establishments should be considered as a non-invasive, environmentally friendly, and potentially profit-generating measure to mitigate A. catenella -caused damage to the shellfish aquaculture industry. [ABSTRACT FROM AUTHOR]