Joined: Oct. 2002
Interesting new article on the origin of NK cells, a possible "bridge" between innate and adaptive immunity.
|Urochordates and the origin of natural killer cells: Identification of a CD94/NKR-P1-related receptor in blood cells of Botryllus |
Konstantin Khalturin *, Matthias Becker *, Baruch Rinkevich , and Thomas C. G. Bosch *
*Zoological Institute, Christian Albrechts University Kiel, Olshausenstrasse 40, 24098 Kiel, Germany; and National Institute of Oceanography, Tel Shikmona, P.O. Box 8030, Haifa 31080, Israel
Published online before print January 7, 2003
Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0234104100
Transplantation immunity based on the recognition of MHC molecules is well described in vertebrates. Vertebrates, however, do not undergo transplantation reaction naturally. The phylogenetically closest group in which transplantation reactions can occur is the Urochordata. Therefore, these animals occupy a key position for understanding the evolution of the vertebrate immune system. When screening for genes differentially expressed during allorecognition in Botryllus schlosseri, we isolated a gene coding for a type II transmembrane protein with a C-type lectin-binding domain and close similarity to vertebrates CD94 and NKR-P1. Here we show that the gene, BsCD94-1, is differentially regulated during allorecognition and that a subpopulation of blood cells carries the corresponding receptor on its cell surface. Southern blot analysis with DNA from individual colonies and intronless BsCD94-1 probe reveal variation between individuals at the genomic level. CD94 in vertebrates is one of the markers for natural killer cells and binds to MHC class I molecules. Natural killer cells play a major role in recognition and elimination of allogeneic cells. Their evolutionary origin, however, remained unknown. The results presented here indicate that the elaboration of the vertebrate immune system may have its roots in an ancestral population of cells in the urochordate blood.