Communication between the nervous and immune systems has been investigated in terrestrial mammals and suggests that various stimuli such as stress and psychological factors as "perceived" by the brain may have an effect on immunocompetence. Neural-immune interactions were studied in the beluga, Delphinapterus leucas to investigate potential pathways whereby various stressors encountered in the wild or captive aquatic environment may alter immune response and potentially lead to disease.

Beluga lymphoid organs (spleen, thymus, lymph nodes, mesenteric associated lymphoid tissue, tonsil, GALT) were harvested during a sanctioned hunt and processed for light (LM) and electron microscopy (EM). The lymphoid organs examined showed similarities with a few differences to the traditional mammalian lymphoid organ morphology. Immunocytochemistry was carried out on these organs to study the innervation. Antibodies against tyrosine hydroxylase, the rate limiting enzyme in norepinephrine synthesis, and Neuropeptide-Y (NPY), a 36 amino acid peptide often found co-localized with norepinephrine were used to identify noradrenergic and NPY-positive nerve fibers. Noradrenergic and NPY-containing nerve fibers were associated not only with the smooth muscle of the vasculature but were closely associated with lymphocytes. Furthermore, noradrenergic and NPY-positive nerve terminals were seen closely abutting lymphocytes at the EM level.

Beluga peripheral blood lymphocytes were isolated and labeled with an antibody against beluga IgG. Analysis with a fluorescent activated cell sorter indicated an IgG positive population of approximately 10-15%. Preliminary radioligand binding studies showed the presence of beta adrenergic receptors on beluga peripheral blood lymphocytes. Beluga lymphocytes were incubated with norepinephrine and/or NPY in the presence of T and B cell mitogens to look at potential effects of these neurotransmitters on the proliferation response. No effects of norepinephrine or NPY on the proliferation response were apparent. Other immunological assays are currently being carried out to look at the potential functional significance of norepinephrine and NPY on peripheral blood lymphocytes of the beluga as well as on recently harvested lymphocytes from fresh spleen, thymus, and lymph node.

We have demonstrated an anatomical link between the nervous and immune systems in the beluga whereby various physical and psychological stressors may affect immunocompetence. Functional effects of neurotransmitters on beluga lymphocytes are currently being investigated.