The study of the cetacean immune system has become increasingly important for the health maintenance of cetaceans in the wild as well as for those under human care. The incidence of mass die-offs, strandings, disease, and presence of environmental pollutants, has often been associated with a compromised immune system in these mammals. Initial efforts in our laboratory towards the investigation of the cetacean immune system focused on the morphological organization and innervation of lymphoid organs and cells, in the beluga whale, Delphinapterus leucas. These studies demonstrate the need for cetacean-specific reagents in order to further characterize the cetacean immune system.

Most of our efforts for development of cetacean-specific reagents have focused on the isolation of the gene for cetacean CD4, a protein present on the surface of T helper lymphocytes. A 500 base pair fragment of beluga CD4, isolated by PCR amplification, using primers to conserved regions of the human and mouse molecule, was used to probe a beluga cDNA library. Ten clones were identified by the probe, and two of these clones, appearing to have the correct size for the message of CD4, were sequenced. Results indicate approximately 50% identity at the amino acid level with human and mouse CD4.

Presently, we are adapting methodologies for expression of cetacean CD4. Antibodies will be generated against the protein for identification of cetacean T helper lymphocytes in the peripheral blood and organs of healthy cetaceans, as well as sick and/or stranded cetaceans. The same will be carried out for cetacean CD8, a protein found on the surface of cytotoxic T lymphocytes. In addition to its use as a reagent, the study of cetacean CD4 in comparison with human and mouse CD4, may prove insightful in regards to the evolution of the immunoglobulin genes, the recognition of foreign antigens in association with MHC class 11 molecules, and as a receptor for the human immunodeficiency virus.