Marine invertebrate immunodefense responses: Molecular and cellular approaches in tunicates

The reason for analyzing tunicate recognition systems is two-fold. First, they can be established as primitive models for understanding fundamental immunological mechanisms by analyzing either their individual cells in vivo or in vitro. Discovered mechanisms could provide alternatives to traditional mammalian (mouse, rat) and emerging models (fish, amphibians) in answering basic questions concerning immunity and disease. Moreover, their advantages lie in: (a) the simplicity of primitive systems (minimal hemopoietic sites), allowing a more effective dissection of variables; (b) their limited expense when compared to experimentation using vertebrates; and (c) their being socially non-controversial. Second, techniques of cell and molecular biology are equally applicable to tunicates as invertebrate models. Despite the considerable advances of recent years, many fundamental or conceptual aspects of immunological reactivity remain unresolved. A clear understanding of the system's evolutionary past will help to elucidate mechanisms which are complex and difficult to decipher in mammals, as we postulate, the immunorecognition systems of vertebrates evolved from simpler systems. Then tunicate immunodefense responses are excellent examples for analyses.