INVERTEBRATE CYTOKINES - TUNICATE CELL-PROLIFERATION STIMULATED BY AN INTERLEUKIN-1-LIKE MOLECULE

Tunicate pharyngeal cells include lymphocyte-like cells and granular amoebocytes. They are involved in the specific allogeneic and phagocytic reactions of tunicates. Little is known about their regulation or control. A tunicate interleukin 1 (IL-1)-like fraction is shown to stimulate the proliferation of these cells in vitro. This fraction, designated tunicate IL-1-beta, was isolated from tunicate hemolymph by gel filtration and chromatofocusing chromatography. Mitogenic responses to tunicate IL-1-beta were dose dependent and could be eliminated rapidly by removing tunicate IL-1-beta from culture medium. A second tunicate hemolymph fraction had no effect on tunicate cell proliferation even though it exhibited IL-1-like activity in a mouse thymocyte proliferation assay. Phytohemagglutinin did not act synergistically with either fraction. These data are discussed in terms of the function and evolution of IL-1-like molecules in invertebrates.