Histologic analysis of an immune response in the lung parenchyma of mice. Angiopathy accompanies inflammatory cell influx.

To determine the histologic changes occurring during a pulmonary immune response, the lungs of antigen-primed C57BL/6 mice were examined on various days after intratracheal challenge with 10(8) sheep erythrocytes. The response was characterized by 1) dense perivascular aggregates composed largely of mononuclear cells; 2) endothelial cell hypertrophy and subendothelial inflammatory cell collections in vessels of a variety of sizes; 3) variable degrees of focal, reversible vascular injury (angiopathy) of both muscular arteries and small veins; and 4) increased cellularity of alveolar walls. Inflammatory cells appeared to emanate from small veins and venules and from minute thin-walled vessels adjacent to large arteries. The reaction peaked at 3 to 4 days and then gradually declined over a period of 6 weeks, never quite reaching baseline. We believe that this experimental model will be an important means of further defining both the mechanisms of lymphocyte entry to the lungs in response to antigen and the factors controlling the pathogenesis of related angiopathies.