Elements of Adaptive Immunity Self-assemble
Putting together the Team! The mode of installment of the unique genomic sequences (VDJ); recombination activating genes (RAG 1/2); recombination signal sequences (RSS); major histocompatibility complex (MHC), which started to work in unison for the first time in the lymph nodes along the intestinal tract of the ancient sharks is not known. These elements now encode the entire adaptive immune system in vertebrate hosts, which have bone marrow, spleen and thymus. The elements of the entire system were acquired by the ancestral jawed gnathostomata cartilaginous fishes, the primordial sharks, some 500 hundred million years ago. It is presumed that the adaptive immune system was acquired in part through vertical inheritance, and in part through horizontal gene transfers. The horizontal gene transfers were postulated to be those of ancient retrotransposons: Transib transposons encoding rag1 to join a pre-existing rag2 gene)  (Figure 45). Herpesviral infections by the ancestor of the EBV from the amphioxus and sea urchin to the chondrichtyes gnathostomata, and from there upward on the evolutionary ladder, as carriers of the V(D)J/RAG1-2 sequences was also proposed (vide supra). The single elements of the adaptive immune system united first in the Placoderms and sharks; reviewed in [27, 147]. The idea of ancient herpesviral (ancestral EBV) horizontal gene transfer was elaborated on by Dreyfus et al . Neither Dreyfus, nor Sinkovics realized at the time of their publication, that H. H. Niller et al reported first in 2004 at an international conference in Balatonfüred, Hungary, that the EBV genome harbors a sequence identical (co-linear) with a part of the V(D)J genome (vide infra).