Nature of Local Immunity in Lungs of Rabbits Immunized Against Pneumococci. ∗

Abstract

In a series of experiments designed to study the pathogenesis of experimental pneumococcus pneumonia in rabbits by the method employed by Lamar and Meltzer, 1 Winternitz and Hirschfelder 2 and Armstrong and Gaskell, 3 it was found that the intrabronchial insufflation of a broth culture of virulent type I pneumococcus leads to infection of the lungs, with a marked rise in body temperature within 24 hours, usually followed by death of the animal in 1 to 3 days. While pneumococci were recovered from the peripheral blood in only a few of the rabbits before death, blood agar plate cultures of the individual lobes of the lungs, the heart's blood and trachea, taken at autopsy, revealed large numbers of pneumococci. The leukocyte counts were not particularly significant, in that marked increases in numbers were observed in some rabbits and decidedly fewer numbers in others of the same series.

The pathological study of the lung tissues from these animals presents a fairly uniform picture. There is a marked acute inflammatory reaction, the polymorphonuclear leukocyte being the predominant cell of inflammation, with macrophages and lymphocytes in lesser numbers. Eosinophiles are only rarely seen. A diffuse edema of the lungs is common; when areas of consolidation occur they tend to be of a lobular type or the result of dense infiltrations of polymorphonuclear leukocytes in the perivascular and peribronchial lymphatics. The pulmonary lymph follicles are not unusually hyperplastic.