The expression of alpha4 integrins by human polymorphonuclear neutrophils in response to sonicated extracts of Enterococcus faecalis.

This study was undertaken to investigate immunopathologic mechanism of Enterococcus faecalis in relation to persistent apical periodontitis. We monitored the expression levels of alpha4 integrin in human polymorphonuclear neutophils (PMNs) after stimulated with sonicated extracts of E. faecalis (SEF) and compared with lipopolycaccarides (LPS) of Escherichia coli for various incubation time. Venous blood was collected from healthy volunteers and then PMNs were isolated and cultured with various concentrations of SEF for different periods of time. The levels of alpha4 integrin were measured by flow cytometry analysis. E. coli LPS group was used as a positive control and untreated PMNs as a negative control. Results showed that the expressions levels of alpha4 integrin were increased in human PMNs stimulated with E. coli LPS in comparison with unstimulated control cells (p < 0.05). In case of SEF stimulated group, the expression levels were decreased in time-dependent manner in comparison to E. coli LPS group (p < 0.05). Notably, after 12 h for incubation with SEF, the expression of alpha4 integrin was decreased in dose-dependent manner (p < 0.05). These findings suggest that E. faecalis seem to suppress PMNs recruiting activity by down-regulating alpha4 integrin expression, providing the possible mechanism that E. faecalis may play a crucial role in persistent apical periodontitis.