A mouse model of pneumonitis induced by Chlamydia trachomatis: morphologic, microbiologic, and immunologic studies.

Swiss-Webster white mice were infected with Chlamydia trachomatis organisms through intranasal inoculation. It was found that a typical interstitial pneumonitis could be induced. Histopathologic findings showed that the lung infiltration was predominantly polymorphonuclear cells and was most prominant on Day 2. The cellular infiltrate gradually changed to mononuclear cells after Day 3. Intracytoplasmic inclusions were frequently found in the interstitial cells and occasionally in the bronchial epithelial cells. Typical chlamydial bodies (elementary, intermediate, and reticulate forms) were identified by electron microscopy. The organisms were recovered from mouse lungs on Days 1--7, with the highest yields on Day 2. This correlated with the peak of lung infiltration seen by histologic examination. Antibodies specific to the infecting immunotype began to appear between Day 7 and Day 10 after inoculation and lasted until Day 35 without a decline in titers. A delayed hypersensitivity reaction was observed by footpad test from Day 5 to Day 21, with the peak reaction at Day 7. This study showed that the mouse model could be used to study the immunopathogenesis of C trachomatis infection.