Pilot Investigation of Pathogenic Microorganisms in Intracranial Aneurysms and the Associated Inflammation

Abstract

AbstractBackground This research explores whether pathogenic microorganisms are present in the intracranial aneurysmal wall and whether they are involved in the chronic inflammation associated with aneurysms. Methods Multiple tests were performed on the specimens; aneurysms were assessed through quantitative real-time polymerase chain reaction, immunohistochemistry (IHC), fluorescencein situhybridization (FISH), and correlative light and electron microscopy (CLEM). Subsequently, the correlation between the levels of pathogenic microorganisms and inflammation-related indicators (CD14, TLR-2, TLR-4 and CD68) was verified according to the microbial testing results. The revised average optical density (rAOD) method was applied for semiquantitative analysis of immunohistochemical images. Results The presence of bacteria in the aneurysmal walls was revealed by immunohistochemical detection of the bacterial-specific endotoxins lipopolysaccharide (LPS) and lipoteichoic acid (LTA). A positive reaction for LPS occurred in 70.6% of the 51 specimens, and a positive reaction for LTA occurred in 52.9%. The rAOD based on IHC showed that CD14 expression was significantly greater in LPS-positive aneurysm specimens than in LPS-negative aneurysm specimens (P = 0.0003 < 0.05), while CD68 expression was not significantly different between LPS-positive and LPS-negative aneurysmatic specimens (P = 0.513 > 0.05). LPS expression was positively correlated with CD14 expression, r = 0.4405, P = 0.0354 < 0.05. The presence of bacteria in intracranial aneurysms was confirmed by FISH and CLEM. Conclusions The existence of bacteria in the intracranial aneurysm wall was demonstrated with immunohistochemical detection of bacterial-specific endotoxins, LPS and LTA, and further verified through FISH and CLEM observations.