96-31846 Marchalonis The combinatorial immune response of vertebrates is a complex and precisely regulated defense system. An understanding of the fundamental nature and mechanisms of operation of this system may be gained by exploration of its evolutionary origins. This will be done by determining whether the most primitive jawed vertebrates, represented by sharks, possess the genetic and biochemical machinery to generate a completely diverse immune response. Studies have clearly demonstrated that the genes specifying immunoglobulin segments and the biochemical machinery (recombinase activating gene RAG1) necessary for their rearrangement emerged early in the evolution of vertebrates, being definitively present in all gnathanstomes. The high degree of variable region diversity in light chains, in heavy chains, and in the newly discovered immunoglobulin IgW as well as the differences in the arrangement of gene segments have disclosed novel mechanisms that offer new perspectives in understanding the origins and the function of the immune system. The proposed objectives of this grant are: to characterize the shark recombination activating genes RAG1 and RAG2; to determine the structure, genomic organization, and the molecular mechanism for generating diversity in the primordial class of immunoglobulin called IgW; and to determine the genomic organization and diversity of expression of light and heavy chains that are involved in generating the major serum immunoglobulin IgM. The results of these studies should allow investigators to develop realistic hypotheses regarding the origins of combinatorial immune system which is characteristic of vertebrates which in turn should lead to novel approaches to understanding and to manipulating the immune system of all vertebrates. %%% The combinatorial immune response of vertebrates is a complex and precisely regulated defense system. An understanding of the fundamental nature and mechanisms of operation of this system may be gained by exploration of it s evolutionary origins. This will be done by determining whether the most primitive jawed vertebrates, represented by sharks, possess the genetic and biochemical machinery to generate a completely diverse immune response. The results of these studies should allow investigators to develop realistic hypotheses regarding the origins of combinatorial immune system which is characteristic of vertebrates which in turn should lead to novel approaches to understanding and to manipulating the immune system of all vertebrates. ***
