Scavenger receptor A is expressed by macrophages in response to Porphyromonas gingivalis, and participates in TNF-α expression

Introduction:  Porphyromonas gingivalis is a periodontopathic bacterium closely associated with generalized aggressive periodontal disease. Pattern recognition receptors (PRRs) participate in host response to this organism. It is likely that PRRs not previously recognized as part of the host response to P. gingivalis also participate in host response to this organism.
Methods and Results:  Employing qRT-PCR, we observed increased msr1 gene expression at 2, 6, and 24 h of culture with P. gingivalis strain 381. Flow cytometry revealed increased surface expression of SR-A protein by the 24 h time point. Macrophages cultured with an attachment impaired P. gingivalis fimA - mutant (DPG3) expressed intermediate levels of SR-A expression. Heat-killed P. gingivalis stimulated SR-A expression similar to live bacteria, and purified P. gingivalis capsular polysaccharide stimulated macrophage SR-A expression, indicating that live whole organisms are not necessary for SR-A protein expression in macrophage response. As SR-A is known to play a role in lipid uptake by macrophages, we tested the ability of low-density lipoprotein (LDL) to influence the SR-A response of macrophages to P. gingivalis , and observed no effect of LDL on P. gingivalis -elicited SR-A expression. Lastly, we observed that SR-A knockout (SR-A^−/−) mouse macrophages produced significantly more tumor necrosis factor (TNF)-α than wild type mouse macrophages cultured with P. gingivalis .
Conclusion:  These data identify that SR-A is expressed by macrophages in response to P. gingivalis , and support that this molecule plays a role in TNF-α production by macrophages to this organism.