To better understand cetacean immunology, it is important to develop markers that identify specific leukocyte populations. We created a monoclonal antibody (mAb) library against leukocytes of the beluga whale (Delphinapterus leucas), and established five hybridoma clones that produce mAbs. Three of these mAbs (ID: BW-3C3, BW-2G4, and BW-2G6) react with mononuclear leukocytes including lymphocytes and monocytes. mAb BW-3C3 react to a fraction of the lymphocytes. The mAb-positive cells were identical to cells that also stained with polyclonal anti-whale IgM antibodies, indicating that the mAb BW-3C3 specifically reacts to B lymphocytes. mAb BW-2G4 specifically binds to monocytes that possess a reniformed nucleus. mAb BW-2G6 was found to bind to heterogeneous lymphocytes, namely, anti-whale IgM antibody-positive and -negative lymphocyte populations. This indicates that this mAb reacts with B and non-B lymphocyte fractions. The other two mAbs (ID: BW-4B10 and BW-4G12) react with polymorphonuclear granulocytes. Double staining with Giemsa-eosin showed that mAb BW-4B10 and mAb BW-4G12 specifically identify neutrophils and eosinophils, respectively. This panel of mAbs will be a useful tool for classifying leukocytes and for determining their localization in different tissues, which in turn would contribute to our understanding of cetacean immunology and allow evaluation of leukocyte function in infectious diseases.
A serologic survey of Brucella infection was performed in Caspian seals (Pusa caspica, n=71), Baikal seals (P. sibirica, n=7), ringed seals (P. hispida hispida, n=6), and beluga whales (Delphinapterus leucas, n=4) inhabiting Russian waters, by enzyme-linked immunosorbent assay (ELISA) using Brucella abortus and B. canis as antigens. The sera of 4 Caspian seals (4%) tested positive for B. abortus. The same sera samples demonstrated weaker yet detectable affinity for B. canis antigens. Several discrete bands against B. abortus and B. canis antigens were detected on Western blot analysis of the ELISA-positive seal sera; the bands against B. canis were weaker than those against B. abortus. The sera of 3 beluga whales (75%) were positive for B. abortus antigens but showed no binding to B. canis antigens in the ELISA. The positive whale sera showed a strong band appearance only against B. abortus antigens in the Western blot analysis. Many detected bands were discrete, while some of them had a smeared appearance. The present results indicate that Brucella infection occurred in Caspian seals and beluga whales inhabiting Russian waters, and that the Brucella strains infecting the seals and the whales were antigenetically distinct.
Although several Edwardsiella tarda infections have been reported, its pathogenic role in marine mammals has not been investigated at the genome level. We investigated the genome of E. tarda strain KC-Pc-HB1, isolated from the false killer whale (Pseudorca crassidens) found bycaught in South Korea. The obtained genome was similar to that of human pathogenic E. tarda strains, but distinct from other Edwardsiella species. Although type III and VI secretion systems, which are essential for the virulence of other Edwardsiella species, were absent, several virulence-related genes involved in the pathogenesis of E. tarda were found in the genome. These results provide important insights into the E. tarda infecting marine mammals and give valuable information on potential virulence factors in this pathogen.
Cetacean health may be potentially affected by anthropogenic sound. We have initiated investigations on the effect of low-frequency underwater sound on immunological gene transcript profiles of captive bottlenose dolphins (Tursiops truncatus) using a probe-based quantitative gene expression assay. Six immunologic genes (IL-2Rα, -4, -10, -12, TNFα and IFNγ) were selected for analysis using two validated housekeeping genes (PGK1 and HPRT1) as reference genes. Twenty-four blood samples from six clinically healthy individuals and six blood samples from individuals after sound exposures were available. The gene transcript profile of sound-exposed dolphins was consistent with a stress-induced TH2 shift profile as compared to controls. This study may lead to better understanding of the effects of anthropogenic sound on immune responses of cetaceans.
To reveal the reproductive biology in male bottlenose dolphins (Tursiops truncatus), circulating gonadotropins (follicle stimulating hormone [FSH] and luteinizing hormone [LH]) and testicular hormones (testosterone and inhibin) were monitored for 8−12 years in 2 captive bottlenose dolphins (Mars and Regulus). During the study period, Mars was undergoing sexual maturation, whereas Regulus was already mature at the beginning of the study. Assuming that Mars had reached sexual maturity when the significant increase in circulating testosterone levels was observed, serum concentration of inhibin was higher in the sexually immature stage than in the mature stage, whereas the serum concentration of FSH was higher in the sexually mature stage than in the immature stage. No difference was observed in the LH levels between pre- and post-sexual maturation. There was a significant increase in serum concentration of testosterone during spring in both animals. These results suggest that the mechanism responsible for regulating FSH secretion by inhibin functions during the sexually immature stage in this species.