Interactions of tunicate immunomodulatory proteins with mammalian cells

The ability of a tunicate immunomodulatory protein, tunIL1, to interact with mammalian cells was investigated. TunIL1 is known to regulate inflammatory defence reactions in tunicates and to stimulate the proliferation of mammalian thymocytes. In the current study, tunIL1 was shown to enhance L929 fibroblast proliferation, induce IL-2 secretion from human mononuclear cells and enhance IL-2 receptor expression by EL-4 murine lymphoma cells. These biological activities are comparable with those of the mammalian inflammatory cytokine, IL-1. However, tunIL1 does not appear to stimulate its effects on mammalian cells by interacting with cell surface receptors in a manner analogous to mammalian IL-1. TunIL1 cannot block the binding of anti-IL-1 receptor antibodies to EL-4 cells, nor can anti-IL-1 receptor antibodies inhibit the capacity of tunIL1 to stimulate thymocyte proliferation. This indicates that tunIL1 does not induce its IL-1-like activities via structural homology to mammalian IL-1.