Abstract

Natural killer (NK) cells are an important part of the innate immune system of mammals. However, little is known about NK-like cell activity in the eastern oyster (Crassostrea virginica) or American lobster (Homarus americanus), two economically important species, or about the role these cells play in defense against pathogens. NK-like cell activity of oyster and lobster hemolymph cells was measured by a flow cytometric assay in which hemocytes were incubated with DiO-labeled K-562 target cells and propidium iodide to label dead cells. For every individual oyster and lobster tested, higher effector-to-target cell ratios resulted in higher levels of target cell death. Moreover, NK-like activity of individual oysters was further enhanced by recombinant human interleukin-2 (IL-2). There is evidence that IL-2 also enhanced lobster hemocyte NK-like activity. Our data demonstrate for the first time the presence of NK-like cell activity in marine invertebrates. This activity was enhanced by physiologically relevant concentrations of mammalian IL-2, which further suggests that some structural and functional homologues of the mammalian innate immune functions are conserved in invertebrates such as oysters and lobsters.