In vitro and in vivo immune responses in neonatally thymectomized Holstein-Friesian calves exposed to bovine viral diarrhea virus.
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Neonatally thymectomized and normal Holstein-Friesian calves were exposed to bovine viral diarrhea virus and challenged 22 days later. Baseline values in non-specific mitogen induced lymphocyte blastogenesis and serologic responses to tetanus toxoid and Brucella abortus strain 19 were established in neonatally thymectomized and normal calves. Neither viral recovery nor protective antibody production followed the very low level primary exposure to bovine viral diarrhea virus. The expected clinical response to an appropriate challenge inoculum did not occur, however, suggesting an immune response to bovine viral diarrhea virus had been initiated by the primary exposure. Five of eight calves developed protective serum levels of bovine viral diarrhea antibody. This may represent an example of immunologic priming. Exposure to low levels of bovine viral diarrhea virus also has potential implications in the pathogenesis of chronic bovine viral diarrhea wherein low level exposure may interfere with the development of protective levels of bovine viral diarrhea antibody as was observed in three calves. Circulating lymphocyte concentrations and results of non-specific mitogen stimulation of lymphocytes revealed a reduced phytohemagglutinin response in conjunction with a slightly increased response to bacterial lipopolysaccharide and pokeweed mitogen in the presence of moderate lymphopenia. The capacity of lymphocytes to respond to phytohemagglutinin was unchanged but an increased total response, as occurred in control thymectomized and intact calves, did not occur. The response to tetanus toxoid, a thymus-independent antigen, was increased following exposure to bovine viral diarrhea virus, perhaps reflecting an alteration in thymic-independent regulation. The lack of a differential response to Brucella abortus strain 19 implied competence in thymus-dependent helper cells. 1981.
