Past studies have demonstrated substantial physiological similarities between invertebrate and vertebrate immunity. However, such functional similarities might also reflect the convergent evolution of otherwise unrelated systems. Only detailed molecular comparisons will confirm true homology. The long term goal of identifying and characterizing invertebrate recognition molecules is specifically designed to provide such molecular comparisons. Urochordates represent the closest extant ancestor of the chordates, and so have a substantial chance of yielding identifiable molecular homologies with vetebrate immune- related molecules. Monoclonal antibodies directed against urocordate cell surface antigens will be obtained and screened for their capacity to inhibit immunological reactivity in in vitro assays of cytotoxicity and cell proliferation. Inhibitory monoclonal antibodies will be used to purify putative recognition molecules. Unlike previous, unsuccessful investigations, this protocol does not assume that invertebrate recognition structures share similarity with their vertebrate equivalents. i.e. It does not rely on the capacity of anti-vertebrate molecular probes to cross-react with invertebrate determinants, but should identify urochordate recognition structures in the context of their native functions. This project aims to identify and characterize molecules that mediate immunological recognition among invertebrates. Previous analyses suggest that specific immunological recognition is not solely a vertebrate trait. Many invertebrates exhibit adaptive histocompatibility responses that bear considerable similarity to vertebrate immune reactions. Indeed, it is postulated that the adaptive immune systems of higher (vertebrate) animals evolved directly from more primitive systems of recognition that are still expressed among advanced invertebrates. If this hypothesis proves to be true, invertebrates may assume an important role as model systems for the analysis of fundamental imunological mechanisms that remain disguised by the complexity of vertebrate systems. However, before such invertebrate models can be applied to the rationalization of complex problems, the evolutionary homology of vertebrate and invertebrate immunorecognition must be examined. The results of this research on the immunorecognition structures in tunicates should make a substantial contribution toward this goal.
