It can be seen that the insects are the still attracting most research and researchers. However, an increasing interest is emerging to study new invertebrate groups, especially those where the genome is known. Even though Drosophila has been and still is an excellent model for immune studies, it is now clear that there are great differences between immune responses in Drosophila and that of several other invertebrates, which indeed calls for more research on other invertebrates

Based on the assumption that invertebrates as well as vertebrates possess factors regulating hematopoiesis, response to infection or wounding, studies dealing with the evolution of immunity have focused on the isolation and characterization of putative cytokine-related molecules from invertebrates. Until recently, most of our knowledge of cytokine- and cytokine receptor-like molecules in invertebrates has relied on functional assays and similarities at the physicochemical level. As such, a phylogenetic relationship between invertebrate cytokine-like molecules and invertebrate counterparts could not be convincingly demonstrated. In the present book, recent studies demonstrating cytokine-like activities and related signaling pathways in invertebrates are critically reviewed, focusing on findings from molecular biology and taking advantage of the completion of the genome from the fly Drosophila and the worm Caenorhabditis elegans.

The comparative approach to immunology can be traced to the era of Pasteur and Metchnikov in which observations regarding foreign recognition in invertebrates was a factor in the develop ment of the principal concepts that created the foundation of what now is the broad field of immunology. With each major experimental and conceptual breakthrough, the classical, albeit essential, question has been asked "are the immune systems of phylogenetically primitive vertebrates and invertebrates similar to that of mammals?" Somewhat surprisingly for the jawed verte brates, the general answer has been a qualified form of "yes", whereas for agnathans and invertebrate phyla it has been "no" so far. The apparent abruptness in the appearance of the immune system of vertebrates is linked to the introduction of the somatic generation of the diversity of its antigen specific receptors. Therefore the questions regarding the origin and evolution of the specific immune system revolve around this phenomenon. With respect to the origin of the system (aside from the or igin of the rearranging machinery itself, the study of which is still in its infancy) one can ask questions about the cellular and mo lecular contexts in which the mechanism was introduced.

Immunology of Annelids provides a state-of-the-art review of the biological and biochemical processes involved in defense reactions of annelids. The book covers phylogeny, taxonomy, and fundamental body structure to provide basic information essential to developing a full understanding of the defense system of an organism. Physiological aspects of the relationship between the immune systems and cells and their limitations are discussed in detail, and the role of cells in cellular defense, transplantation, and humoral defenses is explained. The importance of annelids and their defense reaction from the phylogenetic standpoint is examined in a chapter comparing vertebrate and invertebrate defense strategies. Immunology of Annelids is a practical reference for cell biologists, immunologists, evolutionary and developmental biologists, and other researchers who need insight into the development and hierarchy of immune reactions.

The biological bases of invertebrate immune responses have interested scientists for decades, from the first relevant observation by E. Metchnikoff in 1882, who discovered phagocytosis while studying starfish larvae. Invertebrate immunology first began to be appre ciated as an important field in the late 1960s and 1970s. However, in the following years there was much controversy regarding the question: do invertebrates offer insight into the origin of the sophisticated immune responses of the vertebrates? There are several reasons why progress in research on invertebrate immune competence has been painfully slow. One of the main impediments to the progress, as compared to the fast development of knowledge in the vertebrate systems, was the fact that most of the studies concentrated on "whole organism" assays, mainly on grafting tissues between allogeneic partners. Only in the last few years have more and more aspects of invertebrate immunity been investigated on the cellular, biochemical and molecular levels. These studies led to discoveries of novel defense reactions, new pathways of effector mechanisms which are elicited after recognition of "nonself', and complex, sometimes highly polymorphic genetic elements that control invertebrate immune reactions. The importance of invertebrate immunity for understanding "immunology" as a whole, despite the conflicting models and hypotheses, is now much more recognized than before. Although most of the 20 phyla belonging to the inver tebrates have different modes of life, body organizations, habitats occupied, and biochemical patterns, they show striking aspects of exceptional precision for discriminating between self and nonself.