Porphyromonas gingivalis increases keratinocyte transfer of HIV-1 to permissive cells

Systemic infection with HIV-1 occurs infrequently through the oral route. This low frequency may be increased by concomitant bacterial infection of the oral tissues, since co-infection and inflammation of some cell types increases HIV-1 replication. Previously, we reported that P. gingivalis gingipains and LPS up-regulate expression of the major HIV-1 co-receptor CCR5 on CCR5-negative oral keratinocytes. Objective: We tested the hypothesis, therefore, that P. gingivalis selectively modulates the outcome of R5-tropic HIV-1 infection of oral epithelial cells. Methods: Immortalized human oral epithelial cells (TERT-2) in the presence or absence of P. gingivalis for 3 h, were washed, inoculated with either X4- or R5-tropic HIV-1, washed and maintained in culture medium for up to 48 h. At selected times, culture supernatants, trypsin-detached HIV-1 and cell lysates were recovered. TERT-2 cells with and without HIV-1 were also visualized by confocal microscopy. In some experiments, TERT-2 cells were incubated with antibody against CCR5. Each fraction was inoculated onto HIV-reporter TZM-bl cells and incubated for 24 h, stained with X-gal and positive blue cells were counted. To estimate newly produced virions, RNA was also recovered and analyzed using real-time PCR. Results: P. gingivalis increased selective transfer of R5-tropic HIV-1 from all cell fractions to permissive cells; transmission of X4-tropic HIV-1 remained unchanged. P. gingivalis also increased cell-to-cell transfer of infectious HIV-1. Oral keratinocytes appeared to harbor infectious HIV-1 with no evidence of productive infection. HIV-1 did not appear to co-localize with P. gingivalis intra- or extracellularly. When CCR5 was blocked with specific antibodies, HIV-1 transfer was reduced. Conclusions: P. gingivalis up-regulation of CCR5 increases trans infection of harbored R5-tropic HIV-1 from oral keratinocytes to permissive cells. Oral infections such as periodontitis may, therefore, increase risk for oral infection and dissemination of R5-tropic HIV-1. Supported by NIH grant-in-aid DE015503.