Influence of selective T-lymphocyte depletion on the lung pathology of gnotobiotic calves and the distribution of different T-lymphocyte subsets following challenge with bovine respiratory syncytial virus

The depletion of CD8(+) T-lymphocytes with a murine monoclonal antibody (mAb) specific for the CD8 molecule delayed the ability of three gnotobiotic calves to clear bovine respiratory syncytial virus (BRSV) from their lungs within 10 days after an experimental challenge with the virus. This protracted infection was associated with an enhanced pneumonic consolidation score (21.6 per cent) compared with seven control calves (7.4 per cent) and a histological lesion of active respiratory epithelial hypertrophy. Three gnotobiotic calves depleted of the CD4(+) subpopulation with the appropriate mAb also had enhanced macroscopic lesions (16.6 per cent) but the histological lesion was less active. The depletion of the gamma/delta TCR(+) WC1(+) subpopulation had no apparent effect on the macroscopic or microscopic pulmonary lesions. Although the depletion of the CD8(+) or the CD4(+) subpopulations enhanced the pulmonary lesions, no clinical signs of respiratory disease were detected. Immunoperoxidase labelling and image analysis of the lymphocyte subpopulations in lung tissue revealed an increase in the number of CD8(+) T cells after the infection of non-depleted, control calves, especially in the lamina propria of the large bronchioles. Calves depleted of individual lymphocyte subsets and infected with BRSV showed no compensatory increase in the remaining subpopulations and no lymphoreticular hyperplasia.