Distribution of Ia antigens and T lymphocyte subpopulations in rat lungs

In order to examine the mechanisms of specific immunity in the lung, the distribution of Ia antigens and T lymphocyte populations was determined using immunoperoxidase-staining of cryostat sections of lungs from specific pathogen-free rats. BALT was found to be divided into three regions of lymphoid tissue. The central region was primarily composed of B cells, and was surrounded by a peripheral region of T cells (MRC OX-19⁺) which included both T helper (W3/25⁺) and T suppressor/cytotoxic (MRC OX-8⁺) cells. The subepithelial region contained a dense network of W3/25⁺, non-T cells. A majority of BALT cells, including the lymphoepithelial cells, were Ia⁺. The alveolar walls were found to contain numerous Ia⁺ dendritic-shaped cells. Alveolar macrophages found in sections, as well as those collected using bronchoalveolar lavage, were Ia^- and W3/25^-. Mechanisms for the induction of immunity within both BALT and the alveolar region are proposed.