Purpose: To study whether B lymphocytes involve in bone resorption in periodontal disease by evaluating RANKL expression of B lymphocytes in immune response to aggregatibacter actinomycetemcomitans (Aa).
Methods: The expression of mRNA transcripts involved in day 1 and day 7 responses of cytokines in cultured rat splenocytes was determined by RT-PCR; The percentage of RANKL-expressing IgG positive cells by B cells in cultured rat splenocytes was measured by flow cytometry; and B lymphocytes capacity for induction of osteoclast differentiation was evaluated by TRAP staining. SPSS 10.0 software package was used for statistical analysis.
Results: The expression of IL-4 and IL-10 in cultured cells was not changed in the presence of Aa on day 1, after culture for 7 days; The percentage of B lymphocytes, all RANKL mRNA transcripts and percentage of RANKL-expressing IgG positive cells were significantly increased in the presence, compared to the absence of Aa. These increases were considerably greater in cells isolated from immunized than non-immunized rats. B cells from Aa immunized rats significantly increased induction of osteoclast differentiation (P<0.01), and addition of human OPG-Fc into the culture significantly inhibited its induction (P<0.05), and was RANKL-independent.
Conclusion: B lymphocytes contribute to bone resorption in periodontal disease through involving in the immune response to Aa, up-regulation of RANKL expression and increasing induction of osteoclast differentiation.