Immunohistochemical characterization of lung lesions induced experimentally by Mycoplasma agalactiae and Mycoplasma bovis in goats

Goats aged 3 months were inoculated with a recent isolate of Mycoplasma aga lactiae (five animals) or Mycoplasma bovis (five animals) by a combined (in tratracheal + intranasal) route. Two control goats were inoculated by the s ame route with sterile mycoplasma broth. Animals were killed 14 or 21 days after infection. At necropsy, tracheal and lung tissue was taken for pathol ogical and immunohistochemical examination to determine changes in the lymp hocyte subpopulations in the bronchus-associated lymphoid tissue (BALT). Co nsolidation of the lungs was not observed in any animal, M. agalactiae or M . bovis was recovered from the respiratory tract and lung of all but two in fected animals. Both Mycoplasma spp. induced a moderate bronchointerstitial pneumonia, characterised by lymphoid hyperplasia of the BALT and infiltrat ion of mononuclear cells into the alveolar walls. The predominant phagocyti c cell in the pulmonary parenchyma and the airways was the macrophage. The main cellular type in the BALT was the CD3(+) T lymphocyte, and the ratio o f CD4(+) CD8(+) cells was >1. It is likely that cellular immune mechanisms, through the activation of CD4+ T lymphocytes, plays a prominent role in th e acute and subacute phase of these infections. (C) 2000 Harcourt Publisher s Ltd.