The cluster of differentiation 81 (CD81)， a member of the transmembrane 4 superfamily， is primarily found to be expressed in a wide variety of cells including T and B cells of vertebrates as a critical modulator. In the present study， the open reading frame of a CD81 gene homolog (Lja-CD81) was cloned in lamprey， Lampetra japonica， which is 702 bp long and encodes a protein of 233-amino acids. Although Lja-CD81 seems to be close to CD9 molecules in their full-length sequences， Lja-CD81 possesses higher identity to vertebrates' CD81 than to CD9 (including a lamprey CD9) molecules in their large extracellular loops. In addition， it also possesses a myristoylation site (Met-Gly-Val-Glu-Gly-Cys-Leu-Ly... More
The cluster of differentiation 81 (CD81)， a member of the transmembrane 4 superfamily， is primarily found to be expressed in a wide variety of cells including T and B cells of vertebrates as a critical modulator. In the present study， the open reading frame of a CD81 gene homolog (Lja-CD81) was cloned in lamprey， Lampetra japonica， which is 702 bp long and encodes a protein of 233-amino acids. Although Lja-CD81 seems to be close to CD9 molecules in their full-length sequences， Lja-CD81 possesses higher identity to vertebrates' CD81 than to CD9 (including a lamprey CD9) molecules in their large extracellular loops. In addition， it also possesses a myristoylation site (Met-Gly-Val-Glu-Gly-Cys-Leu-Lys) in its N-terminal region which is identical to the N-terminal regions of CD81 molecules. These data suggest that CD9 and CD81 molecules diverged no later than the emergence of jawless vertebrates. The mRNA levels of Lja-CD81 in lymphocytes and supraneural myeloid bodies were up-regulated significantly after stimulation with mixed antigens， and a similar expressional pattern of Lja-CD81 at protein level was also confirmed. Furthermore， Lja-CD81 was found to be co-localized with variable lymphocyte receptor B (VLRB) evenly on the cell membrane of peripheral blood lymphocytes isolated from control group， but they were found to aggregate on one side of the membrane of peripheral blood VLRB+ lymphocytes after stimulation with mixed antigens. All these results indicate that the Lja-CD81 identified in lamprey may play an important role in the immune response of lamprey VLRB+ lymphocytes.
