1Texas A&M University, College Station, TX, USA; 2U.S. Navy Marine Mammal Program, SPAWARSYSCEN, San Diego, CA, USA; 3Loma Linda University, Loma Linda, CA, USA; 4The Scripps Research Institute, La Jolla, CA, USA
Evidence from a variety of disciplines supports a bidirectional communication between the nervous system and the immune system. Various kinds of environmental challenges as perceived by the nervous system can affect an animal’s ability to fight off pathogens that may compromise the immune system and result in disease or mortality. Neural-immune interactions have applications for cetaceans in the wild and for those kept under human care. Environmental pollutants (oil, industrial toxins, noise), extreme changes in temperature, housing conditions, social interactions, as well as the level of difficulty in learning a task, have been shown to cause changes in immunocompetence in other mammals.
Our laboratory has investigated aspects of both the nervous and immune systems in cetaceans including: general morphology of cetacean lymphoid organs at the light and electron microscopic levels, the autonomic innervation of lymphoid organs at the light and electron microscopic levels, characterization of lymphocytes in cetacean peripheral blood, functional lymphocyte studies, and molecular characterization of important immunologic proteins. Morphology of cetacean lymphoid organs at the light and electron microscopic levels reveals similar structure to lymphoid organs of other mammals with some unique features. Innervation of lymphoid organs reveal postganglionic sympathetic nerve fibers containing tyrosine hydroxylase (TH) (the rate-limiting enzyme for catecholamine synthesis) and neuropeptide Y are closely associated with lymphoid cells in these organs. Moreover, TH-positive nerve terminals are observed in close apposition with lymphocytes in the spleen at the electron microscopic level. Ligand binding studies show the presence of beta-adrenergic receptors on cetacean peripheral blood lymphocytes. Major histocompatibility class II expression reveals constitutive expression on T lymphocytes as well as B lymphocytes. At the molecular level, the T helper cell surface protein, CD4, reveals differences in immunoglobulin domain structure with an increase in potential glycosylation sites and unique substitutions in the cytoplasmic domain. Preliminary functional investigations show a decrease in proliferation of lymphocytes after incubation with isoproterenol (a beta-adrenergic agonist).
Using available cetacean-specific immunologic reagents that we and our collaborators have developed we are currently measuring immunocompetence and nervous system activation in cetaceans, before, during, and after environmental challenges. Pharmacologic and behavioral means may be applied to lessen the effects on the nervous and immune systems and help to promote health and viability in these mammals.