Changes in lymphocyte subsets in the bronchus-associated lymphoid tissue of goats naturally infected with different Mycoplasma species

The distribution of cells containing lysozyme, S-100 protein, CD3, CD4, CD8 , major histocompatibility complex class II antigen and immunoglubin G (IgG ) was analysed in the bronchus-associated lymphoid tissue (BALT) of goats n aturally infected with three Mycoplasma species. This study included the im munohistochemical characterization of the pneumonic lesions of 18 goats (3- 5 months old) infected with one of the following Mycoplasma species: M. myc oides ssp. mycoides, Large Colony type (goats no 1-6), M. mycoides ssp. cap ri (goats no 7-12) and M. capricolum ssp. capricolum (goat no. 13-18). Micr oscopically, infected animals showed a moderate bronco-interstitial pneumon ia, characterized by lymphoid hyperplasia of the BALT and infiltration of m ononuclear cells in the alveolar walls and airways. The main cellular type in the BALT was represented by CD3(+) T lymphocytes, and the ratio of CD4():CD8(+) cells was >2. The BALT showed large germinal centres mainly compos ed of IgG(+) B lymphocytes, with numerous S-100(+) follicular dendritic cel ls. The presence of follicular dendritic cells confirmed the high degree of organization of this lymphoid tissue. The immunohistochemical results show ed that activated T lymphocytes, particularly in the CD4 subset, and IgG(+) B cells, play a major role in the immune response of the caprine lung infe cted with these species of mycoplasmas.