Background: Previous studies from our laboratory of brain tissues obtained at autopsy have established an association of Chlamydia pneumoniae infection with late-onset Alzheimer's disease. Given these findings, we have designed a translational research study to identify biomarkers associated with Chlamydia pneumoniae infection in the blood of geriatric patients. These biomarkers may be useful as a diagnostic screen in the evaluation of patients for cognitive change consistent with mild cognitive impairment and Alzheimer's disease.

Methods: This translational investigation was approved by the PCOM Institutional Review Board prior to patient recruitment and evaluation. In order to participate, identified patients had to be >65 years old and meet well-defined inclusion criteria. Once informed consent was obtained, these patients were evaluated for cognitive status using the SLUMS and FAST testing assessments. After psychometric testing, blood was drawn from the patients and the buffy coat was isolated and assessed by serology, immunofluorescence microscopy, and electron microscopy to identify biomarkers of infection.

Results: All methods revealed evidence for Chlamydia pneumoniae infection in a subgroup of our patient population. Current analysis of 16 patients by serology demonstrated 14/16 positive for at least one immunoglobulin class, IgM, IgA, or IgG. Analysis by immunofluorescence microscopy of peripheral blood revealed 13/16 patients positive for Chlamydia when labeled with a genus-specific anti-Chlamydial antibody. Of these 13 patients, 6 demonstrated a very strong positivity in monocyte populations. Limited infection was observed for the remaining positive 7 patients. For additional confirmatory studies to identify Chlamydia pneumoniae infection, a subpopulation of the 13 patient samples was prepared for electron microscopy. In these samples, elementary bodies, intra-vacuolar reticulate bodies, and intermediate bodies, characteristic of Chlamydia, were observed in leukocytes from the buffy coat. More specifically, we observed the classical "pear-shaped" elementary bodies characteristic of Chlamydia pneumoniae.

Conclusions: Our data indicate that biomarkers for Chlamydia pneumoniae are present in blood samples from the geriatric patients who participated in this study. These data suggest that these biomarkers could be useful as a diagnostic screen for the geriatric population who may be at risk for developing cognitive decline.