Ultrastructural studies of chlamydia-infected air sacs of chicks

The air sac of chicks inoculated with Chlamydia psittaci was examined ultrastructurally. The epithelial cells had minute chlamydial inclusion bodies consisting of a few reticulate bodies in the initial stages of infection. In the epithelial cells in the early and middle stage of infection, small- to medium-sized chlamydial inclusion bodies were found in the cytoplasm adjacent to the Golgi apparatus and surrounded with many mitochondria. The cytoplasm having chlamydial inclusion bodies was rich in free ribosomes and rough endoplasmic reticulum. Chlamydial inclusion bodies in the epithelial cells in the late stages of infection were enlarged and contained many intermediate and elementary bodies. The cytoplasm of the involved epithelial cells had dilated endoplasmic reticulum, and swollen and degenerated mitochondria, and were poor in ribosomes and myelin figure-like structures. Subsequently, the epithelial cells were desquamated from the air sac wall. Macrophages and a few heterophils also were infiltrated into the intercellular spaces. Chlamydiae multiplied actively in the macrophages. It was concluded that airsacculitis was initiated with epithelial cell changes resulting from chlamydial multiplication.