Serotype b of Aggregatibacter actinomycetemcomitans increases osteoclast and memory T‐lymphocyte activation

Abstract

During periodontitis, alveolar bone resorption is associated with activation of T helper type 17 (Th17) lymphocytes and receptor activator of nuclear factor-κB ligand (RANKL) -induced osteoclasts. We previously reported that serotype b of Aggregatibacter actinomycetemcomitans has a higher capacity to trigger Th17-type differentiation and function in activated T lymphocytes and its lipopolysaccharide is a more potent immunogen compared with the other serotypes. This study aimed to investigate whether serotype b of A. actinomycetemcomitans induces higher Th17-associated RANKL production, RANKL-induced osteoclast activation, and antigen-specific memory T lymphocyte proliferation. On naive CD4(+) T lymphocytes stimulated with autologous dendritic cells primed with different A. actinomycetemcomitans serotypes, RANKL production, T-bet, GATA-3, RORC2 and Foxp3 expression, RORC2/RANKL intracellular double-expression, TRAP(+) osteoclast activation, and bone resorption were quantified. The frequency of proliferating memory T lymphocytes in response to A. actinomycetemcomitans serotypes was determined in periodontitis and healthy subjects. Naive CD4(+) T lymphocytes stimulated by serotype b-primed dendritic cells elicited higher levels of RANKL, RORC2, TRAP(+) osteoclasts, and bone resorption than the same cells stimulated with the other serotypes. RANKL positively correlated and co-expressed with RORC2. Memory T lymphocytes responding to serotype b were more frequently detected in periodontitis patients than healthy subjects. These results indicate that serotype b of A. actinomycetemcomitans is associated with higher production of RANKL and these increased levels are associated with Th17 lymphocyte induction, osteoclast activation, and bone resorption.

Inhibitory effect of serotype a of Aggregatibacter actinomycetemcomitans on the increased destructive potential of serotype b

“…Furthermore, the MMP‐2 and MMP‐9 production favor the local soft periodontal tissue breakdown (Bodineau et al, ; Jotwani et al, ). On the other hand, Th1 and Th17 types of cytokines produced by infected DCs induce the production of RANKL and subsequent osteoclast activation and bone resorption (Melgar‐Rodríguez et al, ; Song et al, ). Interestingly, it has been reported that some immature CD1a + DCs are able to express RANKL (Page & Miossec, ).…”

“…To assess the osteoclast differentiation and activation in response to A. actinomycetemcomitans , DC culture supernatants were used to carry out in vitro osteoclastogenesis assays by determining the expression of the osteoclast‐specific marker tartrate‐resistant acid phosphatase (TRAP) as previously described (Melgar‐Rodríguez et al, ). Briefly, mouse macrophage‐monocyte RAW 264.7 cells (ATCC ® TIB‐71™) were cultured in 24‐well culture plates at 5 × 10 3 cells/well in supplemented DMEM with 35 ng/ml rhRANKL for 4 days.…”

“…The osteoclast resorptive activity was analyzed by quantifying the resorption‐pit areas produced in the presence of DC culture supernatants from each experimental condition as previously described (Melgar‐Rodríguez et al, ). Briefly, RAW 264.7 cells were cultured at 1 × 10 3 cells/well in the same conditions as described above in an osteoassay 96‐well plate (Corning ® Osteo Assay Surface).…”

“…Aggregatibacter actinomycetemcomitans ( A. actinomycetemcomitans ) is a highly pathogenic bacteria strongly associated with the etiology of periodontitis (Schacher et al, ); however, not all bacteria strains belonging to the A. actinomycetemcomitans species have the same immunogenicity (Díaz‐Zúñiga, Melgar‐Rodríguez, et al, ; Díaz‐Zúñiga et al, ; Melgar‐Rodríguez et al, ; Monasterio et al, ). Indeed, seven distinct serotypes are recognized for A. actinomycetemcomitans based on the differential antigenicity of the O‐polysaccharide component of their lipopolysaccharide (LPS) (Takada et al, ).…”

Pathogenicity of Aggregatibacter actinomycetemcomitans in the light of recent research

“…Wykazano, że lipopolisacharyd serotypu b A.actinomycetemcomitans szczególnie silnie aktywuje ekspresję genów różnicujących komórki T do subpopulacji Th 17 , co może prowadzić do nasilonej aktywności resorpcyjnej osteoklastów, a w konsekwencji do agresywniejszego przebiegu zapalenia przyzębia (3). Lipopolisacharyd ten szczególnie silnie aktywuje komórki Langerhansa, prowadząc z kolei do różnicowania i aktywacji Th 17 oraz sekrecji powiązanych z tą linią komórkową cytokin prozapalnych, jak IL-6, IL-17 i IL-21, a także produkcji RANKL i nadmiernej aktywacji osteoklastów (28).…”