Ultrastructural Analysis of Chlamydia Pneumoniae in the Alzheimer's Brain.

We recently reported identification of the bacterium Chlamydia pneumoniae in affected brain regions of patients with Alzheimer's disease (AD) (Balin et al., 1998). In this report, we extend those initial observations to demonstrate that, in addition to the frequently described, standard morphological forms of the organism, pleiomorphic forms are also present in the AD brain. All AD and control brain tissues examined were verified to be PCR-positive and negative, respectively, for the organism. DNA sequence determination of PCR products so derived from total DNA of infected AD brains, as well as from total DNA of cell lines infected with the organism following isolation from these same patient samples, confirmed the presence of organism in relevant samples. Various morphologic forms of C. pneumoniae were identified in PCR-positive tissues and these were characterized based on membrane structure, core density, size, and immunolabeling profiles. Structures identified include the typical pear-shaped elementary body, as well as larger, spherical and oblong reticulate bodies. Intact C. pneumoniae were found both intracellularly and extracellularly in the sampled autopsy brains. Intracellular organisms were located principally within microglia, astroglia, and presumptive pericytes. These results suggest that C. pneumoniae found in cells indigenous to the AD brain do not conform universally to the classical morphology observed in other infected cell types. This pleiomorphism may reflect an adaptive response and/or persistent state of infection for these organisms in Alzheimer's Disease.