In research into the association between "C. pneumoniae" infection and atherosclerosis and coronary artery disease, serological testing, direct pathologic analysis of plaques, and "in vitro" testing suggest infection with "C. pneumoniae" is a significant risk factor for development of atherosclerotic plaques and Atherosclerosis. "C. pneumoniae" infection increases adherence of macrophages to endothelial cells "in vitro" and aortas "ex vivo". However, most current research and data are insufficient and do not define how often "C. pneumoniae" is found in atherosclerotic or normal vascular tissue.