HIV-1 Reactivation Induced by the Periodontal Pathogens Fusobacterium nucleatum and Porphyromonas gingivalis Involves Toll-Like Receptor 4 and 9 Activation in Monocytes/Macrophages

Abstract

Although oral coinfections (e.g., periodontal disease) are highly prevalent in human immunodeficiency virus type 1-positive (HIV-1 ؉ ) patients and appear to positively correlate with viral load levels, the potential for oral bacteria to induce HIV-1 reactivation in latently infected cells has received little attention. We showed that HIV-1 long terminal repeat (LTR) promoter activation can be induced by periodontopathogens in monocytes/ macrophages; nevertheless, the mechanisms involved in this response remain undetermined. Since Toll-like receptor 2 (TLR2), TLR4, and TLR9 activation have been involved in HIV-1 recrudescence, we sought to determine the role of these TLRs in HIV-1 reactivation induced by the periodontal pathogens Fusobacterium nucleatum and Porphyromonas gingivalis using BF24 monocytes/macrophages stably transfected with the HIV-1 promoter driving chloramphenicol acetyltransferase (CAT) expression and THP89GFP cells, a model of HIV-1 latency. We demonstrated that TLR9 activation by F. nucleatum and TLR2 activation by both bacteria appear to be involved in HIV-1 reactivation; however, TLR4 activation had no effect. Moreover, the autocrine activity of tumor necrosis factor alpha (TNF-␣) but not interleukin-1␤ (IL-1␤) produced in response to bacteria could impact viral reactivation. The transcription factors NF-B and Sp1 appear to be positively regulating HIV-1 reactivation induced by these oral pathogens. These results suggest that oral Gram-negative bacteria (F. nucleatum and P. gingivalis) associated with oral and systemic chronic inflammatory disorders enhance HIV-1 reactivation in monocytes/macrophages through TLR2 and TLR9 activation in a mechanism that appears to be transcriptionally regulated. Increased bacterial growth and emergence of these bacteria or their products accompanying chronic oral inflammatory diseases could be risk modifiers for viral replication, systemic immune activation, and AIDS progression in HIV-1 ؉ patients.

Diverse Toll-Like Receptors Mediate Cytokine Production by Fusobacterium nucleatum and Aggregatibacter actinomycetemcomitans in Macrophages

“…Endosomal TLR9 can recognize certain types of bacterial DNA (unmethylated CpG DNA), which results in the production of proinflammatory mediators such as TNF-␣ and iNOS/NO by macrophages (30). A previous study revealed that bacterial DNA from F. nucleatum can lead to TLR9 activation in monocytes (8). In addition, BMDMs used in this study highly express the TLR9 gene compared with alveolar and peritoneal macrophages, and CpG oligodeoxynucleotide (ODN) induces the production of cytokines (IL-6, TNF-␣, and IL-12p40) in BMDMs (31).…”

“…TLR9 deficiency led to decreased production of tumor necrosis factor alpha (TNF-␣) in group B Streptococcus (GBS)-infected macrophages (7). Although it is known that F. nucleatum infection elicits TLR9 activation in monocytes (8), the role of endosomal TLRs in the immune response of macrophages against periodontal bacteria has yet to be clearly elucidated. Therefore, in the present study, we sought to identify TLR signaling-mediated immune responses in macrophages against the periodontal pathogens F. nucleatum and A. actinomycetemcomitans.…”

The oral commensal, Streptococcus gordonii, synergizes with Tat protein to induce HIV-1 promoter activation in monocytes/macrophages

“…[30, 31] We and others have shown that activation of transcription factors, such as NFkB upon Toll-like receptor engagement by bacteria, appears to play a critical role in pathogen-induced HIV-1 promoter activation from latently infected cells. [23, 32] Oral commensals are the predominant species at the oral mucosa and can be similarly recognized by TLRs enhancing activation of host cell transcription factors involved in HIV-1LTR positive regulation such as NFkB. [33, 34] Whether or not these bacteria induce HIV-1LTR activation remains to be determined.…”

“…[19-21] Bacterial extracts from each microorganism were obtained as we have previously reported. [22, 23] Briefly, 5 colonies grown on blood agar plates were placed into 25 ml of corresponding broth and incubated for 24h. Then, bacterial cultures were transferred into 500 ml of the same broth, and incubated under the same conditions for 24h.…”

“…periodontal disease) and systemic inflammatory disorders differentially enhance HIV-1LTR promoter activation in T cells, monocytes/macrophages and dendritic cells, [17] and HIV-1 recrudescence induced by P. gingivalis and F. nucleatum in monocytes/macrophages involves Toll like receptor-2 (TLR2) and TLR9 activation, as well as host cell transcription factors such as NFκB and Sp1. [18] An interesting observation from those studies was that oral periodontopathogens induced a significant HIV-1LTR promoter activation in the BF24 monocytes/macrophages model, which harbors the HIV-1LTR promoter, but not critical HIV-1 transcriptional regulators such as Tat. In addition, we were not able to detect HIV-1LTR promoter activation in BF24 cells exposed to the oral commensals S. gordonii and S. sanguinis .…”