Repeat bacterial challenge in a subcutaneous chamber model results in augmented tumour necrosis factor-alpha and interferon-gamma response, and suppression of interleukin-10

The present study compared the effect of a single or a repeat challenge wit h the Gram-negative pathogen Porphyromonas gingivalis on the local inflamma tory response within subcutaneous chamber model in mice. Subcutaneous chamb ers were implanted 2 weeks prior to the final challenge. The repeat-challen ge (REP) group received two intrachamber bacterial injections 14 days apart , while the single-injection group (SIN) received only a single bacterial c hallenge. Injection of saline was used as the control. The cellular content s of the chamber exudates were used for differential cell counts, and the s upernatants were analysed for tumour necrosis factor-alpha (TNF-alpha), int erferon-gamma (IFN-gamma), and interleukin (IL)-10 levels. Immunoglobulin G 1 (IgG1) and IgG2a levels to P. gingivalis in the exudates were also determ ined. The results showed that the leucocyte counts increased significantly post-challenge, and the REP group showed the highest number of lymphocytes and neutrophils. Both P. gingivalis-challenged groups exhibited significant increase in TNF-alpha and IL-10 levels at day 1 post-challenge. TNF-alpha levels in the chamber exudate were threefold higher in the REP group compar ed with the SIN group on day 1 post-challenge (P < 0.05). In contrast, IL-1 0 levels were significantly lower in the REP group 1 day post-challenge com pared with the SIN group. The REP group had significantly higher levels of IFN-gamma at baseline, and this difference remained significant 1 day post- challenge. Analysis of antibody levels to P. gingivalis showed that while t he control and the SIN groups had no anti-P. gingivalis IgG in the chamber exudate during the 7-day study period, the REP group showed high anti-P. gi ngivalis IgG levels. In addition, the titres of IgG2a were fivefold higher than the IgG1 titres. The results showed that a repeat local challenge with P. gingivalis augmented the proinflammatory cytokines TNF-alpha and IFN-ga mma, while inhibiting the accumulation of the anti-inflammatory cytokine IL -10. This shift towards a T helper 1 (Th1)-dominant response was reflected in the relatively high anti-P. gingivalis IgG2a titres in the local inflamm atory environment 7 days post-challenge.