To investigate the role of bronchus-associated lymphoid tissue (BALT) in delayed-type hypersensitive reaction of the lung, we examined light microscopic findings of the lung and BALT in both normal rabbits and rabbits sensitized intravenously (IV), subcutaneously (SC), and intratracheally (IT) with heat-killed bacillus Calmette-Guerin (BCG).
The rabbits were divided into 5 groups according to the route of sensitization as follows: nonsensitized control group, primary immune response group (IV group), and secondary immune response groups (SC→IV, IV→IV, IV→IT group).
The following results were obtained.
1) BALT in normal rabbits was seen along the air way from main bronchus to bronchioles. BALT was divisible into 4 different areas: lymphoepithelial layer (LE), dome area (DA), follicular area (FA), and parafollicular area (PFA). LE was nonciliated epithelia, and devoid of mucous goblet cells. Massive infiltration of small lymphocytes could be seen, and there was also a slight degree of infiltration of macrophages and plasma cells in LE. FA had characteristics of B cell zone, and postcapillary venules with high endothelium could befound in PFA.
2) Alveolitis and epithelioid cell granulomas were seen in the lungs of all BCG-sensitized groups. The rabbits of IV→IV group developed most extensive granulomatous response in the lungs. There was marked accumulation of pyroninophilic lymphocytes and plasma cells around the granulomas and within the alveolar septa.
3) In the BALT of the secondarily IT sensitized group (IV→IT group), 2 days after secondary sensitization an acid fast organism could be found within a large sized mononuclear cell of LE. In the BALT of the IV sensitized groups (IV, SC→IV, IV→IV group), acid fast organisms could not be seen, but epithelioid cell granulomas could be found.
4) In the course of granulomatous response in the lungs induced by the BCG-sensitization, the number of BALT with FA decreased 2-4 days after secondary IV or IT sensitization in the secondary immune response groups and after primary IV sensitization in the primary immune response group, and then recovered gradually. In LE and DA the number of pyroninophilic lymphocytes and plasma cells increased.
The above results suggest that BALT may induce the local immune response in the lung by uptake of antigen and control the production of immunoglobulins in FA, which may modify the delayed-type hypersensitive reaction in the lung.
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