A histological and immunohistochemical study of the humoral immune system of the lungs in young thoroughbred horses

Lungs were obtained from 16 Thoroughbred horses, aged 1 day to 2 years, which had died or been humanely killed for reasons unrelated to disease of the lower respiratory tract. The lungs were then subjected to a histological and immunohistochemical examination of the humoral immune system. At birth there was no evidence of organized lymphoid tissue, and lymphocytes and plasma cells were virtually absent in all tissue compartments in the first week of life. However, by 12 weeks; foals exhibited well developed bronchus-and bronchiole-associated lymphoid tissue, but this had regressed progressively at and 2 years of age. Plasma cells were present in large numbers in the walls of bronchi and bronchioles in foals aged 8 to 12 weeks. IgA-producing plasma cells were common in the lower respiratory tract of these young horses, in addition to IgG- and Ig;IgM-producing plasma cells. (C) 1999 W.B. Saunders Company Limited.