Endogenous
retroelements are a class of ancient defective viral insertions contained in the genome of host cells, where they account for up to 40% of all
DNA. Centuries of co-existence in host genome have led to the development of immunotolerance to endogenous
retroelements, most of which are defective and unable to replicate or transcribe functional
proteins. However, given their capacity to move across the nuclear and mitochondrial genome and recombine, they could mix phenotypes and give rise to
infections that may trigger innate and adaptive immune responses by sensing receptors capable of recognising foreign
nucleic acids and
proteins. It has recently been suggested that they play a role in the pathogenesis of
autoimmune diseases on the grounds of their partial reactivation or the epigenetic control of host gene transcription. A number of studies have confirmed their contribution to the development of
rheumatoid arthritis,
multiple sclerosis and
systemic lupus erythematosus, but there is still a lack of data concerning
systemic sclerosis (SSc). Their role in the pathogenesis of SSc can be hypothesised on the basis of mitochondrial and nuclear chromatinic damage, and hyper-activation of the immune pathway involved in
antiviral defense. SSc is characterised by genetic and immunological evidence of a
viral infection but, as no viral agent has yet been isolated from SSc patients, the hypothesis that partial reactivation of endogenous retroviruses may trigger the disease cannot be excluded and deserves further investigation.