Serotype a of Aggregatibacter actinomycetemcomitans down-regulates the increased serotype b-induced cytokine and chemokine production in dendritic cells

Objective: In Aggregatibacter actinomycetemcomitans, different serotypes have been described based on LPS antigenicity. Mixed infection with the different A. actinomycetemcomitans serotypes is frequent in periodontitis patients; accordingly, the role of this bacterial species in the pathogenesis of periodontitis may differ depending whether patients or periodontal lesions harbour one or more of the A. actinomycetemcomitans serotypes. We hypothesized that different combinations of these serotypes could be associated with distinct host responses and hence different inflammatory patterns. This investigation was aimed to assess whether the increased immunostimulatory potential attributed to the serotype b of A. actinomycetemcomitans on immune cells is able to be modified during co-infection with other A. actinomycetemcomitans serotypes. Methods: Dendritic cells (DCs) were obtained from healthy subjects and stimulated with the different A. actinomycetemcomitans serotypes or their purified LPS using the following stimulatory conditions: serotype a, b, or c, and the combinations a + b, a + c, b + c, or a + b + c. The cytokine, CCR, and CCL levels were quantified by qPCR and ELISA. Results: Higher levels of cytokines, CCRs, and CCLs were induced when DCs were stimulated with the serotype b of A. actinomycetemcomitans compared with the same cells stimulated with the other serotypes. When DCs were co-infected, these levels decreased in comparison with the serotype 6-stimulation alone, in particular when the serotype a was present in the mixed infection. Conclusions: The increased immuno-stimulatory potential attributed to the serotype b was modified when DCs were co-infected with other A. actinomycetemcomitans serotypes, in particular, when the serotype a was present, the DC response diminished.