Table 1 Summary of key points discussed in the text

• HCMV infection does not appear to be a causative agent of RA.

• HCMV may increase local inflammation caused by P. gingivalis in periodontitis.

• This increase may occur either through immune response or through intrinsic action.

• RA patients seropositive for HCMV display lower bone erosion.

• HCMV inhibits OC differentiation through the induction of QKI5.

• HCMV may also participate in lowering bone erosion through the induction of IFN-α and IL-10 and by producing viral IL-10. IFN-γ produced during the immune response may be involved in this inhibition process.

• Our hypothesis is that HCMV is an aggravating agent of RA on the one hand while seropositivity reduces bone erosion possibly through QKI5 expression on the other hand, although a combination of other mechanisms certainly applies.