Response to neonatally thymectomized Holstein calves to bacille Calmette Guérin.

Neonatally thymectomized and intact Holstein calves were inoculated intradermally with bacille Calmette Guérin mycobacteria at 4 to 6 months of age. The immune response of the calves was evaluated by in vitro lymphocyte stimulation, with a purified protein derivative of Mycobacterium bovis, and by a cervical skin test. Eight of te calves had been previously infected at 7 to 15 weeks of age with bovine viral diarrhea virus. The cutaneous and in vitro immune responses were not different in neonatally thymectomized calves, whether or not they had been previously infected with bovine viral diarrhea virus. However, a prominent histologic difference in the nature of the primary granulomatous lesions was observed in the thymectomized calves. These injection sites were characterized by few lymphocytes and an increased number of multinucleated giant cells. These observations were interpreted as manifestations of a deficient thymus-dependent effector response in the thymectomized calves.